INSTRUMENTATION MAINTENANCE
VALVES AND ACTUATORS
TRAINING MANUAL
Course EXP-MN-SI040
Revision 0
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
INSTRUMENTATION MAINTENANCE
VALVES AND ACTUATORS
SUMMARY
1. OBJECTIVES ..................................................................................................................6
2. INTRODUCTION .............................................................................................................7
2.1. LOCATION IN A REGULATION LOOP.....................................................................7
2.2. DEFINITION..............................................................................................................8
2.3. ROLE OF THE VALVE..............................................................................................8
2.4. CONSTRAINTS.........................................................................................................8
2.4.1. Due to the fluid ..................................................................................................8
2.4.2. Due to the effect of the environment on the valve .............................................9
2.4.3. Due to the effect of the valve on the environment .............................................9
2.4.4. Due to the assembly conditions.........................................................................9
2.5. TECHNOLOGY OF A REGULATION VALVE .........................................................10
2.6. CHARACTERISTICS OF REGULATION VALVES .................................................12
2.6.1. Inherent flow characteristic..............................................................................12
2.6.1.1. Definition ....................................................................................................12
2.6.1.2. The linear characteristic .............................................................................12
2.6.1.3. The equal percentage characteristic ..........................................................13
2.6.1.4. The quick opening characteristic................................................................14
2.6.1.5. Inherent adjustment coefficient or rangeability ...........................................14
3. VALVE TYPES ..............................................................................................................15
3.1. LINEAR ACTION VALVE ........................................................................................15
3.1.1. Plug type valve with single-seat body..............................................................15
3.1.2. Plug type valve with double-seat body ............................................................17
3.2. CAGE VALVE .........................................................................................................19
3.3. 3-WAY VALVE ........................................................................................................21
3.4. DIAPHRAGM VALVE ..............................................................................................23
3.5. VERTICAL LIFT GATE OR GUILLOTINE VALVE...................................................24
3.6. MICRO-FLOW CONTROL VALVE WITH ADJUSTABLE Cv ..................................25
3.7. ROTARY VALVE.....................................................................................................27
3.7.1. Butterfly valve..................................................................................................27
3.7.2. Spherical plug ball valve, known simply as a "Ball valve"................................28
3.7.3. Semi-rotary valve with eccentric shutter ..........................................................30
4. TYPES OF PLUG ..........................................................................................................33
4.1. QUICK OPENING LINEAR PLUG...........................................................................34
4.2. LINEAR PLUG ........................................................................................................34
4.3. MODIFIED LINEAR PLUG ......................................................................................34
4.4. EQUAL PERCENTAGE PLUG................................................................................35
4.5. PARABOLIC PLUG .................................................................................................35
5. TYPES OF CAGE ..........................................................................................................36
5.1. QUICK OPENING CAGE ........................................................................................36
5.2. LINEAR CAGE ........................................................................................................36
5.3. EQUAL PERCENTAGE CAGE ...............................................................................37
5.4. LOW NOISE CAGE.................................................................................................37
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 2 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
6. THE CAP .......................................................................................................................38
6.1. THE PACKING GLAND...........................................................................................39
6.2. GLAND PACKING...................................................................................................40
7. THE SERVOMOTOR.....................................................................................................42
7.1. PNEUMATIC SERVOMOTOR ................................................................................43
7.1.1. Standard diaphragm type servomotor .............................................................43
7.1.1.1. Operation ...................................................................................................44
7.1.1.2. Description .................................................................................................45
7.1.2. Diaphragm type servomotor with multiple springs ...........................................46
7.1.3. Rolling diaphragm type servomotor .................................................................46
7.1.4. Piston type servomotor....................................................................................47
7.2. HYDRAULIC SERVOMOTOR.................................................................................49
7.2.1. Constitution .....................................................................................................49
7.2.2. Operation.........................................................................................................50
7.3. ELECTRIC SERVOMOTOR....................................................................................51
7.3.1. Servomotor with motor and gearbox ...............................................................51
7.3.2. Solenoid type servomotor................................................................................52
7.4. DIRECTION OF ACTION ........................................................................................53
7.4.1. Direction of action of the valve body................................................................53
7.4.2. Direction of action of the servomotor ...............................................................54
7.4.3. Direction of action of the positioning device ....................................................54
7.4.4. Special case with the "two-way" servomotor type piston .................................55
7.5. FAIL-SAFE POSITION ............................................................................................55
7.5.1. Fail-safe aspect of the valve (body + servomotor)...........................................55
7.5.2. Fail-safe aspect of the valve with its positioning device ..................................56
8. VALVE ACCESSORIES ................................................................................................57
8.1. POSITIONING DEVICE ..........................................................................................57
8.1.1. Pneumatic positioning device ..........................................................................58
8.1.1.1. Features .....................................................................................................58
8.1.1.2. Constitution ................................................................................................58
8.1.1.3. Principle of operation .................................................................................59
8.1.1.4. Faults .........................................................................................................61
8.1.2. Electro-pneumatic positioning device ..............................................................62
8.1.2.1. Constitution ................................................................................................62
8.1.2.2. Principle of operation .................................................................................63
8.1.2.3. Faults .........................................................................................................65
8.1.3. Intelligent (digital) positioning device ...............................................................65
8.1.3.1. Constitution ................................................................................................65
8.1.3.2. Principle of operation .................................................................................66
8.1.3.3. Faults .........................................................................................................68
8.2. THE ELECTRO-PNEUMATIC CONVERTER (I/P)..................................................69
8.3. THE LUBRICATOR .................................................................................................70
8.4. THE POSITION SENSOR.......................................................................................71
8.4.1. Microswitch......................................................................................................71
8.4.1.1. Microswitch on a linear valve .....................................................................72
8.4.1.2. Microswitch on a rotary valve .....................................................................73
8.4.2. Inductive limit switch........................................................................................73
8.4.3. Capacitive limit switch .....................................................................................74
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 3 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.5. THE BOOSTER.......................................................................................................75
8.6. ELECTROVALVE OR "ELECTRO-DISTRIBUTOR VALVE" ...................................77
8.6.1. Pneumatic distributor valve .............................................................................77
8.6.1.1. Purpose......................................................................................................77
8.6.1.2. Principle of operation .................................................................................78
8.6.1.3. Diagrams....................................................................................................79
8.6.1.4. The 3/2 distributor valve .............................................................................79
8.6.1.5. The 5/2 distributor valve .............................................................................79
8.6.2. Control of distributor valves .............................................................................80
8.6.2.1. The monostable distributor valve ...............................................................81
8.6.2.2. The bistable distributor valve......................................................................81
8.6.3. Installation of the distributor valve ...................................................................82
8.6.4. The solenoid....................................................................................................83
8.7. MANUAL CONTROL...............................................................................................84
9. MAINTENANCE.............................................................................................................86
9.1. REPLACEMENT OF SEAL PACKINGS..................................................................86
9.2. VALVE CALIBRATION............................................................................................88
9.2.1. Calibration of an I/P converter .........................................................................88
9.2.2. Calibration of an electro-pneumatic positioning device ...................................90
9.2.2.1. Zero adjustment .........................................................................................90
9.2.2.2. Adjustment of the scale ..............................................................................91
9.2.2.3. Replacement of the solenoid......................................................................91
9.2.2.4. Rocker alignment .......................................................................................92
9.3. DEFECTIVE OPERATION OF THE I/P POSITIONING DEVICE ............................93
9.3.1. Pneumatic system check.................................................................................93
9.3.2. Electrical system check ...................................................................................93
9.3.3. Cleaning of the pneumatic system ..................................................................95
9.3.3.1. Calibrated orifice ........................................................................................95
9.3.3.2. Controller....................................................................................................95
9.4. MAINTENANCE OF SERVOMOTOR FOR ROTARY VALVE ................................97
10. TROUBLESHOOTING.................................................................................................99
10.1. CAVITATION AND VAPORISATION ....................................................................99
10.1.1. Variation of the static pressure in a valve ......................................................99
10.1.2. Cavitation ......................................................................................................99
10.1.3. Vaporisation ................................................................................................100
11. VALVE SIZING ..........................................................................................................101
11.1. THE Cv AND THE Kv of a VALVE ......................................................................101
11.1.1. What is the Cv of a valve?...........................................................................101
11.1.2. What is the Kv of a valve? ...........................................................................102
11.1.3. Standard formulae for calculation of a valve Cv ..........................................103
11.1.4. Cv calculation formulae according to the manufacturer Masoneilan ...........103
11.1.4.1. For liquids in imperial units.....................................................................103
11.1.4.2. For liquids in metric units........................................................................104
11.1.4.3. For gases and steam, in imperial units...................................................105
11.1.4.4. For gases and steam in metric units ......................................................106
11.1.5. Cv calculation for a valve.............................................................................107
11.1.5.1. Equivalent Cv with 2 valves in parallel ...................................................107
11.1.5.2. Equivalent Cv with 2 valves in series .....................................................107
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 4 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11.2. CHOICE OF VALVE............................................................................................108
12. TAG AND IDENTIFICATION OF VALVES.................................................................109
12.1. ALL-OR-NOTHING VALVES...............................................................................109
12.1.1. Blow Down Valve ........................................................................................109
12.1.2. Emergency Shut-Down Valve......................................................................109
12.1.3. Remote Operated Valve ..............................................................................109
12.1.4. Shut-Down Valve.........................................................................................110
12.1.5. Surface Safety Valve ...................................................................................110
12.1.6. Surface Controlled Sub-Surface Safety Valve.............................................110
12.2. REGULATING VALVES ......................................................................................111
13. APPENDICES............................................................................................................112
13.1. CRITICAL CONSTANTS OF CERTAIN LIQUID AND GAS BODIES..................115
14. EXERCISES ..............................................................................................................119
15. FIGURES...................................................................................................................122
16. TABLES .....................................................................................................................126
17. ANSWERS TO THE EXERCISES .............................................................................127
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 5 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
1. OBJECTIVES
The purpose of this course is to provide a future instrument engineer with knowledge of all
the types of valves and actuators on an industrial site which has a predominantly
petroleum-related activity.
At the end of the course, the trainee should have the following knowledge concerning
valves and actuators:
Knowledge of all existing types of regulating valve,
Ability to change the direction of action of a valve,
Knowledge of the accessories of a regulating valve,
Ability to distinguish between an I/P converter and an electro-pneumatic positioning
device,
Ability to adjust a regulating valve,
Basic knowledge of how to calculate the Cv of a valve.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 6 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
2. INTRODUCTION
2.1. LOCATION IN A REGULATION LOOP
In a regulation loop, the final adjustment component is usually an automatic valve which,
by acting on the flow-rate of a fluid (gas or liquid), enables the measured value to be
regulated:
Pressure
Flow-rate
Level
Temperature, etc.
The automatic valve is the final component of a regulation system; it is the component that
acts directly on the process.
In a regulation loop, it is every bit as important as the "sensor-transmitter" and as the
"regulator".
W
Y
REGULATOR
CONTROL
COMPONENT
"Valve"
GR
PROCESS
X
MEASURING
COMPONENT
"Sensor Transmitter"
Figure 1: Location of the "regulating valve" in the regulation loop
W : Setpoint
Y : Control signal from the regulator
GR : Adjusting value
X : Measurement from the sensor-transmitter
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 7 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
2.2. DEFINITION
Valves are components with a variable orifice, which enable a fluid flow to be adjusted.
They are the actuators of most regulation systems, and this means that they are
significantly important components. It is for this reason that the catalogues issued by valve
manufacturers are extremely well presented and constitute the best possible
documentation on the subject.
The role of the instrument engineer is often limited to the maintenance and adjustment of
installed valves.
Sometimes, when observing the operation of regulation systems that are not performing
properly, it can be observed that the valve is operating in an abnormal manner: this almost
always occurs very close to the closing point or, conversely, the valves are too often found
to be fully open.
2.3. ROLE OF THE VALVE
A regulating valve modifies a fluid flow-rate (adjustment value), as a function of the signal
from a regulator (control signal) or a transmitter, and it does this whatever the constraints
connected with the circulation of the fluid.
2.4. CONSTRAINTS
2.4.1. Due to the fluid
The fluid is either a liquid or a gas (or vapour), or it can be a two-phase mixture (liquidsolid, water-steam), and these states depend on certain service conditions and the
chemical composition of the fluid.
Examples:
Corrosive fluid: this may or may not attack the materials,
Toxic fluid: danger in case of leakage; sealing class,
Flammable fluid
Explosive fluid: in the presence of air or a spark,
Dangerous fluid: in the sense of a molecular transformation or a reaction with
other products (e.g. Oxygen (O2) with grease),
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 8 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Viscous fluid
Fluid laden with solid particles: erosion, clogging, etc.
Change of phase: solidification, vaporisation, cavitation, etc.
Pressure
Temperature: High, very high, or very low (cryogenic effect),
Food product.
2.4.2. Due to the effect of the environment on the valve
Explosive Atmosphere,
Corrosive Atmosphere,
Dry or Humid Atmosphere,
Salty Atmosphere (Sea-front company),
Vibrations,
Interference (electric motor, thunderstorm, etc.).
2.4.3. Due to the effect of the valve on the environment
Noise: acoustic decibels (dBA),
Vibration: screw tightness problem.
2.4.4. Due to the assembly conditions
Nominal diameter of pipe
Space remaining for shut-off valves and bypass valves.
All these conditions will have a determining effect on the choice and type of valve to be
used in an operating process.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 9 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
2.5. TECHNOLOGY OF A REGULATION VALVE
The valve is broken down into two separate assemblies:
The body
The actuator
Figure 2: Technology of a regulating valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 10 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 3: The two assemblies of a regulating valve
The actuator is a component than enables the passage area to be modulated by
changing the position of the rod that supports the shutter.
The body comprises the body of the valve with its seat, shutter, studs, etc., and the
packing gland cap.
Note: The flow running through the body is a function of the passage area, but also of the
pressure upstream of the flange.
It is the element of the valve that is connected to the pipe, and through which the fluid
flows.
Small valves are connected by means of "unions".
Large valves are connected by means of flanges or by welding.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 11 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Comment:
The actuator can be:
A simple hand wheel: this is known as a "manual" valve or a "hand" valve,
An electromagnet: with two states, energized or not energized; this is an all or
nothing electric valve,
A cylinder,
An electric motor,
A servomotor: This is the name generally given to the device located above the
body, and which functions with pneumatic power.
As the cylinder, the electric motor and the servomotor are all "powered", they can be
remote controlled and still therefore be used for analog and digital regulation.
2.6. CHARACTERISTICS OF REGULATION VALVES
2.6.1. Inherent flow characteristic
2.6.1.1. Definition
This is the law that represents the flow-rate as a function of the displacement of the plug
(or shutter), for a constant ∆P.
There are three fundamental characteristics:
The linear characteristic,
The equal percentage (equal %) characteristic,
The quick opening characteristic.
2.6.1.2. The linear characteristic
The flow changes linearly as a function of the signal. The characteristic is a straight line.
Equal increases in the valve signal cause equal increases in flow-rate.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 12 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 4: Linear flow characteristic
2.6.1.3. The equal percentage characteristic
The characteristic is an exponential function. Equal increases in the valve signal cause
equal increases in relative flow-rate.
Figure 5: Equal percentage flow characteristic
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 13 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
2.6.1.4. The quick opening characteristic
Figure 6: Quick opening flow characteristic
This characteristic consists of a rapid increase in flow at the beginning of the opening
range, reaching approximately 80 % maximum flow for less than half the command signal.
It is also known as an "All or Nothing Flow characteristic ".
This characteristic is very often used for safety applications with All or Nothing valves.
2.6.1.5. Inherent adjustment coefficient or rangeability
A regulating valve can only provide efficient adjustment within a specified flow range. This
is defined by a coefficient R.
R = (maximum controllable flow-rate) / (minimum controllable flow-rate)
Rangeability defines the ability of a valve to control low flow-rates. This means that a valve
with a rangeability of 100 will be capable of controlling a minimum flow-rate that is 100
times less than the maximum flow-rate.
Another way of saying this is that the adjustment range is from 1 to 100.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 14 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3. VALVE TYPES
We will begin by presenting the various types of valve body.
The size of the regulating valve body is proportional to the displacement of the shutter.
There are two body types:
Longitudinal bodies: Translational displacement of the shutter. Usually known
as "Linear Valves",
Angular bodies: Rotational displacement of the shutter. Usually known as
"Rotary Valves".
3.1. LINEAR ACTION VALVE
These valves are also called "standard valves". The shutter is a plug which is displaced by
the servomotor with a translational movement.
3.1.1. Plug type valve with single-seat body
ADVANTAGES
DISADVANTAGES
Good to very good sealing
Relatively high pressure differentials
Relatively simple construction
Requires a large servomotor (high pressure
on the plug)
Table 1: Advantages and Disadvantages of the single seat
The position of the plug in front of the seat determines the passage area for the fluid. L
Sealing around the stem is achieved using Teflon
packing (for example).
The shape of the plug determines the static
characteristic of the valve. Good sealing can be
obtained when the valve is closed because the plug
presses against the mating face of the seat.
Figure 7: Fluid displacement in a single-seat body
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 15 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
The thrust of the fluid against the plug can be very high in cases of high pressure
differentials, requiring the use of a powerful servomotor.
The figure above clearly shows how the fluid flows as it passes through a single seat body.
This provides a better view of the operation of the valve when the plug stem rises and lifts
the plug off its seat.
1
2
3
4
5
6
7
8
9
10
Plug stem
Packing gland flange studs
Packing gland flange nut
Packing gland flange
Packing gland bush
Packing gland seal
Packing gland spacer
Cap
Body studs
Body stud nuts
11
12
13
14
15
16
17
18
19
Body seals
Plug guide
Cage
Seat
Seat seal
Plug
Plug pin
Body
Top nut
Figure 8: Single-seat body
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 16 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.1.2. Plug type valve with double-seat body
1
2
3
4
5
6
7
8
9
10
Plug stem
Packing gland flange nut
Packing gland flange
Packing gland flange stud
Top nut
Cap
Body
Plug pin
Plug
Bottom flange
11
12
13
14
15
16
17
18
19
Body stud nut
Body stud
Body seal
Plug guide
Lower seat
Upper seat
Packing gland seal
Seal spacer
Packing gland bush
Figure 9: Double-seat body
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 17 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
The forces on the shutter system tend to balance themselves out due to the fact that the
fluid attempts to open one plug and to close the other.
These weak forces improve the stability of the valve, which means that a smaller diameter
servomotor can be chosen for a valve of the same capacity.
Most shutter systems are also reversible.
They do not provide very good sealing when closed, due to the fact that both plugs can
never be perfectly seated on their respective seats at the same time.
Figure 10: Fluid displacement in a double-seat body
The above figure shows the same fluid displacement principle as seen in a double-seat
body.
ADVANTAGES
DISADVANTAGES
The forces are almost perfectly balanced
Inferior sealing to that of the single seat
No need for a large servomotor
More complex design
Table 2: Advantages and Disadvantages of the double seat
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 18 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.2. CAGE VALVE
This is a single-seat / plug type valve which also has the advantages of the double seat /
plug valve.
The shutter system incorporates an excellent guide for
the plug (piston) and enables the cage (cylinder) to be
quickly replaced.
The possibility of installing an O-ring around the piston
reduces the likelihood of leakage.
The piston is balanced, because the downstream
pressure acts on both sides of these faces.
The preferential flow direction is from the outside to
the inside of the piston, to ensure better stability.
The cage openings are machined according to the
flow characteristic.
Figure 11: Cage valve
Comment:
There are different types of cage:
balanced or non-balanced cage,
single or double seat cage,
low-noise cage,
anti-cavitation cage.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 19 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
ADVANTAGES
DISADVANTAGES
Excellent ability to withstand large pressure
differentials
More complex design
Excellent sealing
Non-reversible straight body
Low noise
Possible jamming of the shutter in the cage
when using fluids laden with solid particles
Balancing by holes in the shutter
Anti-cavitation
Easy to replace the cage
Anti-flash
Can be used under extreme conditions:
velocity up to 130 m/s
operating temperature -200 to +600 °C
pressure up to 2,500 bars
Easy and quick to maintain
Table 3: Advantages and Disadvantages of the cage valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 20 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.3. 3-WAY VALVE
3-way valves are designed to regulate either a fluid mixing process or a fluid bypass. It
should be particularly noted that this type of valve has a high flow capability and a low
recovery.
The flow capability is among the best of all currently-available 3-way valves. Pressure
recovery is small.
These valves are also designed to be installed with the fluid tending to open the double
plug (mixing valve) or each of the plugs (bypass valve). This configuration has the
advantage of ensuring stable operation of the valve.
Figure 12: 3-way mixing valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 21 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 13: 3-way bypass valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 22 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.4. DIAPHRAGM VALVE
The diaphragm valve is an alternative to the spherical plug ball valve. It is used as an Allor-Nothing valve in small applications (e.g. hot water injection to clean a level sensor
flange separator, etc.).
It is controlled by an "electrovalve" (also called a “solenoid
valve” refer to the valve accessory chapter). When the opening
command is given, the solenoid of the electrovalve is energised
and therefore sends the air from the distributor into the valve
head, and this distorts the diaphragm which in turn allows the
fluid to flow through the body of the valve.
It is used in applications where the fluids are heavily laden with
solid particles or are very corrosive. The passage area is
obtained between a deformable diaphragm, usually made of
synthetic rubber, and the bottom part of the valve body.
Figure 14: Diaphragm valve
Fs
Flexible diaphragm
FP
Figure 15: Functional diagram of the diaphragm valve
The force "Fs" developed by the servomotor must overcome the force "Fp" created by the
static pressure on the diaphragm.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 23 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
ADVANTAGES
DISADVANTAGES
Usable with any type of product
Valve which changes with use (due to the
elasticity of the diaphragm)
Low pressure losses
Temperature less than 120 °C
Inexpensive solution
Unspecified characteristic
No need for packing glands and their
possible leakage
Very imprecise adjustment
Low maximum pressure rating
Badly defined static characteristic
Table 4: Advantages and Disadvantages of the diaphragm valve
3.5. VERTICAL LIFT GATE OR GUILLOTINE VALVE
Figure 16: Guillotine valve
ADVANTAGES
Low pressure losses (direct flow)
DISADVANTAGES
Sharp fluid passage cut-off
Table 5: Advantages and Disadvantages of the guillotine valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 24 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.6. MICRO-FLOW CONTROL VALVE WITH ADJUSTABLE Cv
1
2
3
4
5
6
7
8
Body
Seat
Plug
Seat seal
Seat clamp ring
Seals
Packing gland bush
Packing gland spacer
9
10
11
12
13
14
15
Packing gland flange
Packing gland flange studs
Packing gland stud nuts
Safety plug
Valve coefficient adjustment
Cap
Manual control
Figure 17: Micro-flow control valve with adjustable valve coefficient (Varipak)
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 25 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
The possibility of adjusting the Cv on this
needle valve eliminates valve sizing
uncertainties; such uncertainties often
lead to the choice of a valve that turns
out to be too large and works with an
excessively small opening.
The Cv flow coefficient of the Varipak is
adjustable without changing the
pneumatic control signal. This very easy
manual operation can be carried out
before installing the valve, but it can also
be performed when the valve is
operating.
The plug on this type of valve is a needle.
Figure 18: Example of a micro-flow valve
Figure 19: Adjustment of the Cv
To find out what the Cv of a valve is, refer to the "Valve Sizing" chapter of this course.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 26 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.7. ROTARY VALVE
3.7.1. Butterfly valve
The shutter is a disk whose diameter is equal to the inside diameter of the duct. When
closed, the surface of this disk is perpendicular to the fluid flow direction. The variation of
the passage area is achieved by tilting this disk away from the vertical.
The stem of the shutter rotates, which is much better for the packing gland (better sealing).
This rotation is often limited to an opening angle of 60°, due to the extent of the torque
applied by the fluid.
Figure 20: Butterfly valve
ADVANTAGES
DISADVANTAGES
Direct flow valve (the fluid path is relatively
undisturbed when the butterfly is fully open)
Tendency to cavitate
The butterfly rotates with or without a stop
(the stop provides better sealing)
The poor balancing limits the acceptable
pressure differential, even when the
butterfly is inherently balanced due to its
shape.
Simple and robust design
Valve mostly used for gases and large
diameter pipes
Table 6: Advantages and Disadvantages of the butterfly valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 27 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
This type of valve can only be manufactured for large diameters ND > 4". Considering the
surface area and shape of the shutter, it cannot be used for very high pressures. Due to
the long length of the mating surface of the butterfly on the body (which also constitutes
the seat), sealing in the closed position is difficult to obtain, and is therefore usually poor.
Also note that there is friction due to the thrust of the liquid, which presses the shutter stem
against the seal (transverse effort).
3.7.2. Spherical plug ball valve, known simply as a "Ball valve"
Figure 21: Ball valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 28 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Contains a sphere or ball with a nominal diameter which is generally equal to that of the
pipe.
The ball can pivot through 90° thanks to a stem coupled
to a servomotor.
The ball is in continuous contact with an O-ring, which
provides excellent sealing.
Standard ball valves are used in safety systems (All or
Nothing), or as regulating valves.
Modified ball valves with a "V"-shaped opening have an
equal percentage characteristic, and are suitable for fluids
which are viscous or laden with solid particles or fibres.
The fluid tends to close the shutter system, and the
servomotor must counter this effect.
Figure 22: Example of a ball valve
ADVANTAGES
DISADVANTAGES
Shutter consisting of a hollow sphere with a
cut-out that depends on the required
inherent characteristic
Tendency to cavitate
Direct flow valve, for viscous or fibre-laden
fluids
Good sealing
Accepts high pressure differentials
Table 7: Advantages and Disadvantages of the ball valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 29 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
3.7.3. Semi-rotary valve with eccentric shutter
Figure 23: Valve with eccentric spherical shutter
The principle of operation is based on a spherical shutter with an eccentric rotary
movement, inside a direct-flow body. The spherical part of the shutter is connected by one
or two flexible arms pressed onto the shaft.
The actuator pushes the lever to a varying extent based on the pneumatic signal it
receives, and this causes the shaft to rotate and therefore the shutter to rotate as well.
A slight lateral play of the hub on the shaft enables the shutter to self-centre.
The extremely efficient sealing between the seat and the shutter is obtained by elastic
distortion of the shutter arms.
The slightly chamfered seat is secured inside the body by means of a threaded clamp ring.
This type of valve is regularly used in industrial applications, and is universal.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 30 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 24: Cross-sectional view of the eccentric spherical shutter
Figure 25: Functional diagram of the eccentric spherical shutter valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 31 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
ADVANTAGES
DISADVANTAGES
Direct flow valve with a small footprint,
usually installed between flanges
Greater tendency to cavitate than straight
valves, but not as much as butterfly valves
Suitable for viscous and particle-laden
fluids
Good sealing with a Teflon or plastic coated
contact surface
Table 8: Advantages and Disadvantages of the eccentric shutter valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 32 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
4. TYPES OF PLUG
To obtain the 3 fundamental characteristics described above, we need to change the type
of plug on a valve. This plug will modify the flow of fluid passing through the valve body.
Figure 26: Different plugs and their flow characteristics
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 33 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
4.1. QUICK OPENING LINEAR PLUG
A maximum increase in flow is obtained for a displacement of approximately 30 %, and
this increase then diminishes as the displacement approaches 100 %.
These plugs are mainly used in All-or-Nothing regulation loops and in safety systems.
Figure 27: Quick opening plug
4.2. LINEAR PLUG
The flow is directly proportional to the
opening of the valve over the entire length
of its displacement.
These plugs are used in level regulation
loops, and more generally in processes
with a constant gain.
Figure 28: Linear plug
4.3. MODIFIED LINEAR PLUG
These plugs are a compromise between the linear and quick opening characteristics.
In extreme areas with high flow-rates, and more
particularly with low flow-rates, a long displacement
produces a small variation in flow.
Figure 29: Modified linear plug
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 34 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
4.4. EQUAL PERCENTAGE PLUG
Equal increments in plug displacement
produce equal increases in flow.
Near the closing point, variations in flow
are small; between 0 and 30 % displacement, the flow varies from 0 to
approximately 9 %.
Figure 30: Equal percentage plug
Near the full open point,
variations in flow are relatively
high; between 80 and 100 %
displacement, the flow varies
by approximately 50 %.
These plugs are used in pressure regulation loops, and more generally in
processes where only a small proportion of the total pressure differential can
be absorbed by the valve.
Figure 31: Equal percentage plug turned with a Vee-shaped aperture
4.5. PARABOLIC PLUG
These plugs are a compromise between the linear and equal percentage characteristics.
They have a linear characteristic with high flow and displacement characteristics.
These plugs are used in pressure
regulation loops, and more
generally in processes where a
high proportion of the total
pressure differential can be
absorbed by the valve.
Figure 32: Parabolic plug
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 35 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
5. TYPES OF CAGE
In the same way as for plugs, cage valves have different types of cage which modify the
flow characteristic.
The quick opening, linear, and equal percentage characteristics are determined by the
shape of the openings in the cage.
5.1. QUICK OPENING CAGE
Figure 33: Quick opening cage
5.2. LINEAR CAGE
Figure 34: Linear cage
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 36 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
5.3. EQUAL PERCENTAGE CAGE
Figure 35: Equal percentage cage
5.4. LOW NOISE CAGE
Figure 36: Low noise cage
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 37 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
6. THE CAP
This part is installed on the top of the valve body, and its purpose is to provide sealing
around the plug stem.
It acts as a guide for the plug stem(s), contains the packing gland and supports the
servomotor.
For temperatures >= 200 °C, cooling fins are provided.
For temperatures <= 20 °C, an extension type cap is used
Figure 37: Diagram of valve cap
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 38 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
6.1. THE PACKING GLAND
The packing gland is a very widely used sealing system. Its principle of operation consists
in providing sealing by compression of several braids (packings) around the stem of the
plug by means of the packing gland rammer.
The washers of the packing gland, or the
braids, must seal the body with a minimum
amount of friction on the stem of the plug.
They are usually made of a flexible and
compressible material such as Teflon
(t < = 230 °C) or graphite (t > 230 °C).
The material used for the packing gland
depends on the fluid to be sealed.
The pressure on the washers must be properly
adjusted on a periodic basis, in order to
minimise leakage; this is done by means of the
flange and rammer.
Figure 38: Packing gland of a valve
To obtain absolute sealing, a secondary boot can be joined to the plug stem. This is known
as an "extension" or an "extension boot").
The sealing boot ensures total sealing between the valve stem and the
cap. This technology is typically proposed for applications involving toxic,
flammable or explosive fluids for which any leakage could have serious
consequences for personnel and and/or the environment.
Boot
Figure 39: Sealing boot
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 39 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
6.2. GLAND PACKING
In the world of maintenance, the term "Braids" is often used when referring to gland
packings.
There are two types of seal packing:
Packing rings: These are ready-made seals, to the diameter you need.
Figure 40: Graphite and PTFE packing rings
Braids: These are in the form of coils, and it is up to the instrument engineer to
cut them to the correct length so that it corresponds to the diameter of the
rammer.
Figure 41: Examples of graphite and PTFE braids
Both types of braid shown in the figure above are the most commonly used. Graphite
braids are often used on valves in heating systems, operating at very high temperatures
and at high pressures.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 40 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
For all other applications, we use PTFE (Teflon) braid.
During maintenance, it is important to check the packings because we are so used
to simply saying to ourselves "Oh, I had to tighten the packing gland of that valve
because it was leaking a bit".
But it is important to know that by constantly retightening valve packing glands, the
braids end up becoming crushed and no longer provide proper sealing.
Figure 42: Poor sealing, leakage from the packing gland
The figure above show what happens when a valve is not properly maintained.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 41 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7. THE SERVOMOTOR
The servomotor is the component that enables the plug stem of the valve to be actuated.
The force developed by the servomotor serves two purposes:
It counters the pressure acting on the plug;
It ensures the sealing of the valve.
These two criteria determine the sizing of the servomotors. The driving fluid can be air,
water, oil or gas.
The supply fluid (at 1.4 bars or 2.1 bars) is usually air, and the command pressure varies
from 0.2 bars to 1 bar. The following types of servomotor are available:
Standard diaphragm type servomotor (direct or reverse action).
Rolling diaphragm type servomotor, principally used for rotary valves (example:
Masoneilan CAMFLEX valve),
Piston type servomotor, used in applications where very high forces are required.
The command pressure can be very high. The driving fluid can be air, water or
oil,
Electric servomotor, used for rotary valves. An electric motor is associated with a
gearbox, thus enabling very high torque values to be obtained,
Hydraulic servomotor, used on shutdown valves.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 42 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.1. PNEUMATIC SERVOMOTOR
7.1.1. Standard diaphragm type servomotor
Figure 43: Diaphragm type servomotor
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 43 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.1.1.1. Operation
The diaphragm of the servomotor is subjected to 2 forces:
On one side, the force due to the pressure in the servomotor (modulated
pressure from the regulator). It is proportional to the air pressure and to the
surface of the diaphragm (F = P x S).
On the other side, the force due to the compression of the spring which
increases as the spring is compressed.
For a given air pressure in the servomotor, the spring contracts by a length such that the
resulting force (proportional to the shortening of the spring) is equal to the corresponding
motive force.
For each pressure value, the displacement of the diaphragm is transmitted by the stem to
the plug, the displacement of which is proportional to the air pressure exerted on the
diaphragm.
For Split-Range valves (refer to the course on "the regulator and its functions"), calibration
of the valve consists in adjusting:
The tension of the spring, and
The length of the plug stem.
An adjustment system enables the spring tension to be adjusted. If there is no other
resistance on the stem or plug, the valve stem moves through its full range when the air
pressure varies from 200 to 1,000 mbars.
This results in the following correspondence:
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 44 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.1.1.2. Description
The rolling diaphragm type servomotor is the most commonly used.
Figure 44: Simplified diagram of a diaphragm type servomotor
This servomotor consists of:
A rubber diaphragm,
A return spring,
A stem range adjustment.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 45 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.1.2. Diaphragm type servomotor with multiple springs
This servomotor design with multiple return springs
reduces the forces on the plug stem.
Its rolling diaphragm is subjected to less strain,
which means that it wears less.
Figure 45: Cross-sectional view of a servomotor
with multiple return springs
7.1.3. Rolling diaphragm type servomotor
Diaphragm
plate
Spring
stem
Coupling with
the valve lever
Spring
Figure 46: Rolling diaphragm type servomotor
The rolling diaphragm type servomotor consists of a cylinder clamped in a flange by 4 BTR
screws. The rolling diaphragm is secured both to the cylinder and to the piston which is
connected to the position of the spring.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 46 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Unlike the standard servomotor in which the displacement of the diaphragm plate
assembly is small, this type of Servomotor has a large displacement.
The coupling between the servomotor and the lever of the valve consists of a small
cylinder fitted with a circlip.
This improves the precision of the positioning for the shutter.
The rolling diaphragm is used in more and more applications and can be found on
spherical plug ball valves and on rotary valves.
Its cost is relatively low and it is extremely easy and quick to maintain.
7.1.4. Piston type servomotor
Figure 47: Piston type servomotor
Piston type servomotors operate at much higher pressures than diaphragm type
servomotors.
These pneumatic or hydraulic pressures can be up to several tens of bars.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 47 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
They are capable of producing much higher forces and of operating over much longer
ranges, and can therefore overcome very high pressure differentials through the valve
body.
Safety valves use pistons:
one-way with return spring to return the
valve to its fail-safe position if there is a lack
of air.
Figure 48: Simplified diagram of a one-way piston
type servomotor for a linear valve
two-way with hydraulic accumulator or
pneumatic tank, used to return the valve to its fail-safe position if there is a lack of
hydraulic pressure.
Air to open the
valve
Air to close the
valve
Figure 49: Two-way piston type servomotor for a rotary valve
Without a return spring, there is no possible fail-safe position.
The two-way servomotor has the particularity of having two air inlets, because we
introduce air on one side of the piston to open the valve, and on the other side of the
piston to close the valve, which is normal because there is no return spring.
Piston type servomotors are very often associated with butterfly valves. They can be used
as All-or-Nothing valves, but they can also be used as regulating valves with an electropneumatic positioning device.
Generally speaking, when a piston type servomotor is used as a regulating valve, this is
because the operating conditions involve very high pressures in large diameter pipes.
They are similar to diaphragm type servomotors in that they can be installed either on a
linear displacement valve or on an angular displacement (rotary) valve.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 48 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.2. HYDRAULIC SERVOMOTOR
7.2.1. Constitution
Figure 50: Hydraulic servomotor
A hydraulic servomotor consists of:
A hydraulic pump,
A hydraulic reservoir,
A hydraulic distributor valve,
A valve control,
The actuator, consisting of one or two cylinders.
This type of servomotor is used in very high pressure processes, in which the operating
pressure can be up to about a hundred bars. It can also be used in low-pressure systems,
but the valve opening takes longer because the hydraulic system has a lot of torque.
In the same way as for the piston type servomotor, the hydraulic servomotor can be a oneway or a two-way device.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 49 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.2.2. Operation
In this simple hydraulic actuator, a
stream of hydraulic fluid can be
directed into either of two chambers.
If hydraulic fluid is added to
chamber 1, the piston moves right,
closing the valve.
When hydraulic fluid is added to
chamber 2, the action is reversed.
Hydraulic pressure pushes the piston
to the left and the valve opens.
For more details concerning the
hydraulic actuator, please refer to the
"Hydraulics and Pneumatics" course.
Figure 51: Functional diagram of the
control of a hydraulic servomotor
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 50 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.3. ELECTRIC SERVOMOTOR
7.3.1. Servomotor with motor and gearbox
Figure 52: Electric servomotor with motor and gearbox
The advantage of this actuator is that we only need an electrical signal to "rotate" the
motor, so the associated valve can either open or close.
This type of motor is reversible because it rotates in both directions. It is equipped with a
gearbox which enables the torque to be reduced, in order to prevent the electric motor
from applying too much force on its rack.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 51 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
This type of actuator is often used on All-orNothing safety valves.
Figure 53: Example of an electric servomotor
7.3.2. Solenoid type servomotor
A solenoid is a coil of electric wire wound around a cylinder in with all the turns in
contact with each other. The induction of the magnetic field generated by a solenoid
is proportional to the number of turns and to the intensity of the current passing
through it, and is inversely proportional to its length.
The solenoid is mounted directly on the valve body.
The valve body has a diaphragm equipped with a
return spring.
This diaphragm is installed on a core, over which the
solenoid is fitted.
Figure 54: Valve with solenoid type servomotor
This type of valve can be classified as an
"electromagnetic valve".
When an electrical signal is injected into the solenoid, this generates a magnetic field
which will act on the spring and cause the diaphragm to distort.
Depending on whether or not the diaphragm is distorted, the plug of the valve will be either
open or closed.
This type of valve is used in low-pressure applications, and
has the advantage of rapidly opening or closing the plug of the
valve.
The valve is installed in line for small applications (e.g. boiler
pilot gas supply, vacuum pump buffer tank water
replenishment, etc.).
The solenoid can be energised at 230 VAC, 110 VAC or
48 VAC (refer to the manufacturer's document).
Figure 55: Example of a solenoid type servomotor
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 52 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.4. DIRECTION OF ACTION
7.4.1. Direction of action of the valve body
The direction of action of the valve body depends on the shutter system (plug + seat).
Direct action valve body: extension of the plug stem closes the shutter system.
Figure 56: Direct action valve body
You will have noticed that the figure on the left shows a single-seat valve body,
and that the figure on the right shows a double-seat body.
Reverse action valve body: extension of the plug stem opens the shutter
system.
Figure 57: Reverse action valve body
Comment:
Some valve bodies are reversible, in other words the action of the plug can easily be
reversed by simple disassembly.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 53 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.4.2. Direction of action of the servomotor
If an air failure occurs, the counter-spring causes the servomotor to move to an extreme
position so that the shutter can move to a completely open or a completely closed position.
These types of servomotor therefore do not pose any particular problem when it comes to
complying with the specification, for direct or reverse action servomotors.
Direct action servomotor: the action is direct, so
when the modulated air pressure increases, the
stem of the plug descends.
Figure 58: Direct action servomotor
Reverse action servomotor: the action is
reversed, so when the modulated air pressure
increases, the stem of the plug rises.
Figure 59: Reverse action servomotor
7.4.3. Direction of action of the positioning device
Direct positioning device: When the input signal increases, the output signal
increases.
Reverse positioning device: When the input signal increases, the output signal
decreases.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 54 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
7.4.4. Special case with the "two-way" servomotor type piston
If an air failure occurs, the piston takes any position depending on the force exerted by the
fluid on the shutter of the valve.
In order to force the position of the shutter, it is therefore necessary to provide a device
comprising both a reserve of compressed air and switching components which enable the
valve to be moved to the selected position in case of failure of the distribution system air
supply.
7.5. FAIL-SAFE POSITION
7.5.1. Fail-safe aspect of the valve (body + servomotor)
When there is no more pressure on the servomotor, the spring returns the valve to its open
or closed position, as defined by the construction of the device.
A "Fail Closed" valve, i.e. one which is closed when there is a lack of air, closes
when there is no longer any pressure on the servomotor.
A "Fail Open" valve, i.e. one which is open when there is a lack of air, opens
when there is no longer any pressure on the servomotor.
The choice depends essentially on the safety conditions for the process.
Figure 60: Valve fail-safe position
Comment: When the positioning device is electro-pneumatic, the chances are it will be of
the direct type.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 55 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 61: Different possibilities for the fail-safe position of a valve
7.5.2. Fail-safe aspect of the valve with its positioning device
Action direction
of positioning
device
Fail-safe
aspect of
the valve
P
S
No supply
Direct
Direct
Direct
Timing sequence of particular states
Open
4 mA
200 mbars
Open
20 mA
1,000 mbars
Closed
Reverse
Closed
Closed
Open
Reverse
Direct
Open
Closed
Open
Reverse
Reverse
Closed
Open
Closed
Table 9: Combinations of valve fail-safe and positioning device positions
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 56 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8. VALVE ACCESSORIES
8.1. POSITIONING DEVICE
What is the purpose of a positioning device?
The positioning device is a device used to slave the displacement of the plug to the control
signal from the regulator.
For the regulation system to operate correctly, it is essential for the displacement of the
plug to remain precisely proportional to the value of the regulator output signal.
However, certain interference forces can hinder the movement of the plug:
Thrust exerted by the fluid (particularly in the case of single seat plugs)
Friction of the transmission stem in the Packing gland
Spring exerting a force which is not precisely proportional to the displacement it
undergoes (hysteresis)
Variation of surface area due to the distortion of the diaphragm, etc.
These forces depend on the operating conditions: severe conditions → High forces
Viscous or solid-laden fluid
High pressure differential, etc.
It is therefore necessary, in order to obtain a plug position that corresponds to the value of
the control signal, to complete the regulation system by a positioning device.
There are 3 types of positioning device that can be adapted to a regulating valve:
Pneumatic positioning device
Electro-pneumatic positioning device
"Intelligent" (digital) positioning device
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 57 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.1.1. Pneumatic positioning device
8.1.1.1. Features
The function of the pneumatic positioning device is to ensure linear or other slaving
between the displacement of the valve and a pneumatic signal output by a regulator.
It also has another function, which is to modify the natural characteristic of a valve by
means of a cam whose profile depends on the required characteristic.
It can also be configured for the "cascaded" (Split-Range) control of several valves, and
can be used with an augmented pneumatic supply enabling it to operate the valves under
higher differential service pressures.
It is also possible to reverse the direction of action of the valves by means of the
positioning device.
8.1.1.2. Constitution
The pneumatic positioning device consists of the following components:
The profiled cam: this is the intermediate component between the reaction
device, the valve actuator and the spring of the positioning device. Its profile
determines the relationship between the position of the shutter of the valve and
the signal output by the regulator. "Linear" or "equal percentage" characteristics
are available by selecting the appropriate sector of the cam.
The controller: this is a small 3-way distributor valve. The valve adjusts the
compressed air flow-rates from the supply to the outlet on the actuator, and from
the outlet to the exhaust orifice. The position of this valve is controlled by the
diaphragm, and determines the discharge pressure of the actuator. The action of
the pneumatic positioning device can be reversed by reversing the supply and
exhaust connections and by changing the cam sector and the orientation of the
lever.
The return spring: this enables the slide valve of the controller to slide in the
distributor valve.
The reaction spring: this enables the cam to be rotated by varying the rotation
of the lever. This variation is due to the pressure exerted on the diaphragm.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 58 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.1.1.3. Principle of operation
The pneumatic positioning device is based on the principle of a force equilibrium device:
the pressure of a pneumatic signal applied to diaphragm opposes the force of a reaction
spring.
In the state of equilibrium, if the pneumatic signal varies, the diaphragm assembly moves.
The movement drives the slide valve of the controller, which is pressed by the return
spring.
The displacement of the slide valve alternately sets the outlet system into
communication with the supply system or with the exhaust system, thus modifying the
pressure applied on the actuator.
The cam transmits the displacement of the valve shutter to the reaction spring.
The valve shutter continues its movement until the force of the spring precisely balances
that developed by the pressure of the pneumatic signal on the diaphragm. In this state of
equilibrium, the position of the valve shutter in front of the seat corresponds to that ordered
by the signal from the regulator.
Output signal
to actuator
Figure 62: Functional diagram of pneumatic positioning device
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 59 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 63: Masoneilan pneumatic positioning device
Figure 64: View of the cam with and its reaction spring
We have already seen, in the features of the positioning device, that the cam can change
the characteristic of the valve - the following table gives the cam positions and cam lever
orientations of a MASONEILAN CAMFLEX II or VARIMAX:
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 60 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 65: MASONEILAN lever orientation and cam position
8.1.1.4. Faults
The main faults you are liable to encounter on this type of positioning device are:
The exhaust orifice is blocked, so the valve will no longer regulate and stays fixed
in a certain position,
The cam has worked loose; this is often due to vibrations,
The slide valve of the controller is blocked; the air in the positioning device
sometimes condenses and produces a little humidity in the slide valve, causing
the slide valve to seize up.
Despite these various minor failures that can occur, the mechanism of this pneumatic
positioning device makes it a very robust device that requires little maintenance.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 61 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.1.2. Electro-pneumatic positioning device
8.1.2.1. Constitution
The electro-pneumatic positioning device is made up of the following components:
A rocker system (nozzle-flapper): the imbalance caused by the variation of the
electrical signal in the electromagnet causes the output signal from the nozzle to
the actuator to vary.
Figure 66: Nozzle-flapper system with electromagnet on I/P positioning device
A cam,
A return spring,
A controller: this is an amplifier relay which will amplify the output signal from
the nozzle to the actuator.
A balancing spring: this enables equilibrium to be achieved between the rocker
system and the cam lever.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 62 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.1.2.2. Principle of operation
The principle of operation is almost identical to that of the pneumatic positioning device.
In actual fact, we have retained the pneumatic valve positioning system with the cam and
its lever, but a nozzle and flapper with an electromagnet have been added to enable the
pneumatic signal of the regulator to be replaced by an electrical signal (4-20 mA).
The purpose is to be able to remotely control the regulating valves.
Here, the controller is not a distributor with its slide valve and push-rod, but an amplifier
relay with a diaphragm.
In this case, the signal from the regulator is no longer a pneumatic signal (0.2 to 1 bar), but
an electrical signal (4-20 mA).
The electrical signal (4-20 mA) will pass through the solenoid, and this will move the
flapper. This results in a change in the nozzle output pressure until the reaction of the ball
located at the end of the nozzle balances out the new force applied on the lever.
The more the electrical signal increases, the closer the flapper will move to the nozzle: the
nozzle output signal to the actuator will also increase and therefore tend to open the valve.
The reverse effect will apply if the signal decreases.
Figure 67: Functional diagram of electro-pneumatic positioning device
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 63 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 68: MASONEILAN type 8013 electro-pneumatic positioning device
We can also change the direction of action of the positioning device, for which it is
necessary to:
Reverse the balancing spring
with respect to the rocker
Figure 69: Direct action: beneath the
rocker
Figure 70: Reverse action: above the
rocker
Reverse the wires of the solenoid on the terminal strip of the positioning device.
Figure 71: Solenoid wire reversal to change the direction of action of the positioning device
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 64 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
A great deal of care must be taken to avoid blocking the rocker with the
wires of the solenoid, otherwise the valve will operate in
"ALL-OR-NOTHING" mode, in other words either wide open or
completely closed. The reason I am telling you this is that it happened
to me once, by mistake.
8.1.2.3. Faults
The main faults on the electro-pneumatic positioning device are:
Balancing spring out of its recess,
Unserviceable solenoid or integrated circuit card,
Solenoid jammed in the core. This is due to humidity in the positioning device and
distortion of the solenoid,
Flapper jammed on nozzle → it is necessary to check the balance of the rocker
with the screw of the small counterweight on the flapper,
Clogged nozzle → The nozzle must imperatively be cleaned with compressed air,
A disconnected solenoid wire.
8.1.3. Intelligent (digital) positioning device
The intelligent positioning device is the latest version of the positioning device, which is
becoming more and more widely used.
8.1.3.1. Constitution
The intelligent positioning device consists of the following components:
A microprocessor: this comprises an eeprom which is used to store the data,
and an FSK module for digital communication between a PC and the positioning
device,
A nozzle-flapper system,
A 3-way distributor valve: this is the controller,
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 65 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
An electromagnet: this is the solenoid with its core, which enables the flapper to
be tilted to varying degrees with respect to the nozzle thanks to the magnetic field
created by the electric current passing through it,
A digital display: it will enable the positioning device to be configured and will
display either the fault diagnosis or all the measurement information of the
positioning device.
This type of positioning device is always supplied at a pressure of 1.4 bars, through a
pressure reducing filter.
The electrical signal from the regulator is always a current signal of 4-20mA.
8.1.3.2. Principle of operation
Figure 72: Functional diagram of intelligent positioning device
The central processing unit, or CPU, is the functional centre of the positioning device. The
mechanical and pneumatic components provide only secondary functions.
The input signal (4-20 mA) and the position measurement signal are cyclically checked by
the CPU and sent to an analog-to-digital converter, thus enabling rapid and precise data
processing.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 66 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
The general program also comprises a self-adjustment routine to automatically adjust the
device on the valve actuator, and also an adaptive self-regulation mode which ensures
optimum control and monitoring of the position irrespective of the operating conditions
(supply pressure variation, for example).
The servomotor is controlled by an I/P converter and a 3-way valve (distributor valve). The
electrical signal from the CPU is proportionally converted into a pneumatic signal which
adjusts the 3-way valve. The passage area is constantly modified to inflate or empty the
servomotor proportionally with respect to the signal.
When the valve position is reached, the 3-way valve is in its neutral position (the air flow is
practically zero).
To make it easier for you to understand the operation, bear in mind that the positioning
device operates as a regulator (refer to the course on "the regulator and its functions").
The 4-20 mA input signal is the setpoint, and the position measurement performed by a
position sensor is the measurement. The CPU compares these two values and sends a
proportional electrical signal to the electromagnet, which will provide the means of acting
on the control component (3-way valve) in order to establish measurement = setpoint.
The standard positioning device is equipped with a local keypad (4 keys) and a 2-line
display. This keypad is used for local configuration and for monitoring of the parameters in
operation. Configuration, commissioning and observation can also be carried out remotely,
via the communication port (FSK module), using a computer.
This communication is based on the HART or FieldBus or PROFIBUS protocols.
You can connect to the device either locally or anywhere on the 4-20 mA link.
The basic model of the positioning device can be modified at
any time (this will depend on the manufacturer) to receive
new functions. It is possible to add cards for analog copying:
this will enable a precise indication of the valve position on a
DCS. Limit switches can also be added.
Figure 73: ABB model TZID-C intelligent positioning device
installed on a linear valve
We can also change the direction of action of the positioning
device (direct or reverse), and also the inherent characteristic
of the valve (equal % or linear) simply by configuring the
positioning device via the local configuration keypad, or
remotely using the appropriate software.
For installation purposes, this type of positioning device has
the necessary standard installation kits enabling it to be
installed on any type of valve.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 67 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
It can be installed on linear or rotary valves, and this is also a simple matter of configuring
the device.
Figure 74: ABB model TZID-C intelligent positioning device
8.1.3.3. Faults
This type of positioning device often suffers electronic failures, which means that
maintenance is a simple matter of replacement, so several intelligent positioning devices
must be kept in stock, as the devices can be considered as "disposable".
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 68 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.2. THE ELECTRO-PNEUMATIC CONVERTER (I/P)
The I/P converter is used in all electronic loops for which the actuator is pneumatic, or for
passing through explosive areas for example (refer to the course on equipment in high risk
areas). It converts standardised electrical signals into standardised pneumatic signals.
The electro-pneumatic converter receives a 4-20 mA electrical signal and converts it into a
200-1000 mbar (0.2-1 bar) pneumatic signal.
The converter is also supplied by an air pressure of 1.4 bars (1400 mbars).
The difference between the I/P converter and the electro-pneumatic positioning device is
that there is no valve position in this case.
In clearer terms, the I/P converter
receives the electrical signal (4-20 mA)
from the regulator and converts it into
pressure (0.2 - 1 bar), which is sent
directly to the "valve head".
This equipment is very useful when a
valve positioning device is unserviceable
and an emergency repair is essential. You
attach this converter to the valve and you
connect the 1.4 bar pneumatic supply, the
pneumatic output signal from the
converter to the valve and the 4-20 mA
signal to the terminal strip of the valve,
and that's all there is to it.
Figure 75: MASONEILAN I/P converter
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 69 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Be careful when installing these I/P converters, because different
manufacturers supply different installation kits.
You can install them either on the valve itself, or on a 2" tube in the
vicinity of the valve.
8.3. THE LUBRICATOR
The seal packing is lubricated in order to facilitate the displacement of the shutter stem
and to maintain the braids of the packing gland so that they do not deteriorate too quickly.
This accessory is rarely used on a regulating valve.
Figure 76: Lubricator on packing gland cap
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 70 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.4. THE POSITION SENSOR
Position sensors are widely used on All-or-Nothing valves to show whether there are any
safety valve discrepancies.
They are also used on regulating valves, whether linear or rotary.
The contacts of these position sensors can be Normally Open (NO) or Normally Closed
(NC).
There are therefore two types of contactor:
Contactor with contact, called a microswitch
Figure 77: Microswitch on regulating valve
Contactor without contact, often called a proximity
sensor. This type of contactor can be either inductive
or capacitive.
Figure 78: Proximity sensor
8.4.1. Microswitch
This type of position switch is used as a safety device on valves, to provide the operator
with an alarm in the case of a valve discrepancy.
Its disadvantage is that the contact becomes quickly worn.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 71 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.4.1.1. Microswitch on a linear valve
Valve open
Valve in intermediate position
Valve closed
Figure 79: Position of microswitch on a linear valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 72 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.4.1.2. Microswitch on a rotary valve
On a rotary valve, the rotation of the
valve drives a cam which trips the
contact shown in the figure below.
On this model, the cam and the
contactor also wear rapidly.
Figure 80: Position of the microswitch
on a rotary valve
8.4.2. Inductive limit switch
Inductive sensors are essential in an
industrial environment. Compared to
mechanical limit switches, they provide conditions which are practically ideal: operation
without contact or wear, high switching frequencies, precise switching and high protection
against vibrations, dust and humidity. Inductive sensors detect all metals without contact.
Inductive sensors use the physical effect of the change of state of a resonant circuit,
caused by eddy current losses in conductive parts.
An LC oscillator circuit generates an alternating high frequency field which is radiated from
the active surface of the sensor.
Figure 81: Functional diagram of an
inductive sensor
When a conductive part enters this
field, eddy currents are formed
according to the law of induction,
and these currents draw energy
from the oscillating circuit.
For this reason, the oscillation
amplitude decreases. This change
is converted into a switching signal.
Thanks to this principle, all metallic
materials can be detected, whether
or not they are moving.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 73 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.4.3. Capacitive limit switch
Capacitive sensors are used for the no-contact detection of objects made of any material.
Unlike inductive sensors, which can only detect metallic objects, capacitive sensors are
capable of detecting non-metallic objects. Typical applications can be found in the
following industries: wood, paper, glass, plastic, food processing and chemicals.
The capacitance between the
active electrode of the sensor and
the ground potential is measured.
An object close to the active
surface affects the alternating
electrical field between these two
"capacitor plates". This applies to
both metallic and non-metallic
objects. In principle, capacitive
sensors work with an RC
oscillating circuit.
Figure 82: Functional diagram of a
capacitive sensor
A minimum variation of the
capacitance is enough to affect its
oscillation amplitude.
The evaluation electronics convert this into a switching signal.
The user can adjust the sensitivity by means of a potentiometer.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 74 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.5. THE BOOSTER
The "Booster" is a pneumatic
amplifier which amplifies the air flow
from the valve positioning device
using the output signal of the
positioning device and its supply
(1.4 bars). This enables a larger
volume of air to be obtained, which
makes it easier to inflate the
diaphragm of the actuator.
Figure 83: Functional diagram of
a Booster
When pressure is introduced through the signal port a
downward force on the upper shutter area is created.
This force is balanced by the output pressure acting against
the lower control diaphragm area. The ratio of signal pressure
to output pressure is determined by the ratio of the effective
areas of the upper and lower diaphragms.
Figure 84: Example of a "‘booster"
If signal pressure is increased above the output pressure
there is a net downward force on the diaphragm assembly
causing the supply valve to open.
Output pressure increases
until equilibrium is achieved.
When signal pressure is
decreased below the output
pressure, the diaphragm
assembly rises, allowing
output air to exhaust through
the vent on the side of the
relay.
Figure 85: Control signal
higher than the output
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 75 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 86: Output higher than control signal
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 76 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.6. ELECTROVALVE OR "ELECTRO-DISTRIBUTOR VALVE"
An electrovalve (also called a solenoid valve) is made up of two components:
A pneumatic distributor valve
A solenoid
It is used on All-or-Nothing valves, and therefore on one-way or two-way valves.
Reminder:
The one-way actuator is a piston type servomotor with a return spring.
The two-way actuator is a dual-piston servomotor, so it is necessary to send air onto one
of the pistons whenever we want to open or close a valve.
8.6.1. Pneumatic distributor valve
8.6.1.1. Purpose
The chambers of a valve actuator, when operating, must be alternately connected to the
pressure and to the exhaust.
We are obviously not going to swap the pipe connections around to achieve this.
So the purpose of the distributor valve is to achieve two possible connection
configurations, depending on an external control signal.
Figure 87: Functional diagram of the distributor valve on an actuator
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 77 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.6.1.2. Principle of operation
Schematically, a distributor valve will consist of a slide valve
drilled with ducts. This slide valve can slide into two
different positions inside the body.
The body is also drilled with orifices which are connected
together in twos, depending on the position of the slide
valve.
Figure 88: Displacement of the slide valve in a distributor
valve
In practice, the slide valves used in distributor valves are
not necessarily manufactured with drilled ducts. Depending
on the manufacturer and on the choice of technology, plugs
or other forms of slide valve than the one shown in the
functional diagram may be used.
The distributor valve that is schematically represented here will be used to supply a twoway actuator (since two ducts have been provided to supply the valve actuator).
A distributor valve will be identified by the number of pipes that can be connected to it (this
is stated as the number of orifices) and the number of positions that the slide valve can
occupy.
The distributor valve that we have defined in the functional
diagrams has:
4 orifices:
one supply,
one exhaust,
one connection to the front chamber,
one connection to the rear chamber;
and 2 positions.
It is therefore a 4/2 distributor valve.
Figure 89: Displacement of the actuator piston as a function
of the displacement of the slide valve in the 4/2 distributor
valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 78 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.6.1.3. Diagrams
Each position of the slide valve in the distributor valve is
represented by one box. As this slide valve has two
possible positions, we will draw two boxes (squares).
The ducts are represented by arrows whose direction
indicates the flow of the compressed air.
The ends of the arrows are located opposite the pipes that
lead to the chambers of the actuator, the air supply and the
exhaust.
At any given moment in time, only one of the two boxes is
used. The pipes are therefore connected to one side only
(the active box). When the slide valve moves, the pipes do
not move; the arrows must be located opposite the ducts.
Figure 90: Schematic representation of a 4/2 distributor
valve
For instrumentation purposes, you will be using 3/2
distributor valves and 5/2 distributor valves.
8.6.1.4. The 3/2 distributor valve
The 3/2 distributor valve is used for one-way servomotors. It
has only one orifice to supply the servomotor because only
one chamber can be connected to the distributor valve.
Figure 91: Schematic diagram of a 3/2 distributor valve
8.6.1.5. The 5/2 distributor valve
The 5/2 distributor valve is used by two-way servomotors in
the same way as 4/2 distributor valves. The 5/2 distributor
valve has one exhaust orifice for each chamber of the
actuator.
Figure 92: Schematic diagram of a 5/2 distributor valve
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 79 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 93: Schematic diagram of a 5/2 distributor valve
8.6.2. Control of distributor valves
Electrical control
Distributor valves are controlled by controlling
the displacement of their slide valves. Control
is obtained by changing the operating
setpoint output by the control section.
Pneumatic control
A large number of control methods are
available, but here are the most common:
Electrical control
Push-button control
Pneumatic control
Push-button control
Roller control
Roller control
Spring control
Figure 94: Schematic diagrams of distributor
valve control methods
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Spring control
Page 80 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.6.2.1. The monostable distributor valve
If the distributor valve has a spring control, it is monostable. This means that only the
position obtained through the action of the spring is stable: in the absence of an external
control signal, the slide valve automatically goes to the spring position.
Figure 95: Diagram of a monostable distributor valve with
pneumatic control
Figure 96: Example of a monostable distributor valve with
electrical control
8.6.2.2. The bistable distributor valve
If the distributor valve has two control devices of the same type, it is bistable. This means
that both positions are stable positions: in the absence of an external control signal, the
slide valve does not move and remains in its current position.
Figure 97: Diagram of a bistable distributor valve with
pneumatic control
Figure 98: Example of a bistable distributor valve
with electrical control
The choice between a monostable or bistable control depends
exclusively on considerations connected with the control section. An
all-to-frequent error consists in thinking that there is a relationship
between the one-way servomotor and a monostable distributor valve.
In our case, for instrumentation, we usually need an electrical control on a monostable or
bistable distributor valve.
The electrical control will be implemented by means of a solenoid, which will be located on
the pneumatic distributor valve.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 81 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.6.3. Installation of the distributor valve
The pneumatic distributor valve fits onto a base, and
this base is used to supply air to the distributor valve
and to distribute the compressed air according to
the displacement of the slide valve in the distributor
valve.
Figure 99: Example of distributor valves mounted on
the base
Figure 100: Example of a base for a pneumatic
distributor valve
The base is connected by means of pneumatic
unions (refer to the course on instrumentation
accessories).
Figure 101: Example of a base for a
pneumatic distributor valves mounted on
a DIN rail in a cabinet
The type of base shown above is designed to
be installed in a cabinet. This base supplies air
to all the pneumatic distributor valves that are
mounted on it.
The major disadvantage of this base is that, if
you need to replace a pneumatic distributor
valve, it
is
necessary to
cut off the air supply to all the distributor valves.
There are also distributor valves that can be
mounted directly on the All-or-Nothing valve using a
standardised installation surface. It is secured onto
the valve by means of two screws.
Figure 102: Example of distributor valves which fit
directly onto the valve, without the need for a base.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 82 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
8.6.4. The solenoid
As I am sure you have understood,
the solenoid will be used to
electrically control the pneumatic
distributor valve.
Solenoid with
connector
You can supply solenoids at
24 VDC, 48 VAC, 230 VAC or
110 VAC.
On industrial sites, they are usually
supplied at 24 VDC.
Solenoid with
connection
Their commands are sent by a plc
or are relayed by a local panel.
As you can see, there is a wide
choice of solenoids.
Dual pulse solenoid
Figure 103: Examples of various
solenoids
Obviously, in order to be able to energise the solenoids, we need a connector through
which the supply wires of the solenoid arrive.
Seal
Figure 104: Connectors used for the electrical connection of the solenoid
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 83 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
A seal is delivered with the connector, to provide sealing between the
connector and the solenoid: it is essential to install this seal on the
connector, otherwise you might get s nasty surprise when it rains!!!!!! Of
course if you decide not to install this seal, get yourself a large box of
spare fuses.
ONCE THE CONNECTION HAS BEEN MADE TO THE CONNECTOR, DO NOT
FORGET TO SCREW THE CONNECTOR ONTO THE SOLENOID: THIS WILL AVOID
"GRRRRRRRRR….."
For everything that concerns the electrical connection details of each instrumentation
accessory, please refer to the "Instrumentation Accessories course".
8.7. MANUAL CONTROL
Manual controls are installed on the servomotor, and their purpose is to enable the valve
to be operated manually in certain cases:
When starting up the unit.
In case of emergency.
In case of a lack of energy on the servomotor.
If the valve is not equipped with a bypass system.
The manual control installed on the top of the servomotor:
can be used as an upward adjustable stop if it has a direct action,
can be used as an downward adjustable stop if it has a reverse action,
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 84 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 105: Manual control installed on the top of the servomotor
The manual control installed on the side of a servomotor can be used as a limit stop in
both directions.
Figure 106: Manual control installed on the side
of the servomotor
The manual control of a valve must only be
used if a problem occurs on the servomotor
or the valve positioning device, for the
purpose of repair. Do not forget to remove
the manual control after completing the
repair!!!
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 85 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
9. MAINTENANCE
9.1. REPLACEMENT OF SEAL PACKINGS
Before doing anything else, it is absolutely essential to check that the valve is no
longer under pressure.
Disassembly of the packing gland:
Loosen and remove the nuts from the rammer
Move the rammer back
Withdraw all the braid rings, using an extractor
Check the surface condition of the braid recess and of the control stem (no
scratches, marks, etc.)
Carefully clean the inside of the packing gland (blow clean with compressed air)
Once this operation has been carried out, it is necessary to repack the packing gland. This
is done by proceeding as follows:
Install the ring (braid) in an "S" configuration.
Offset the cuts by 90° between two rings.
Install one ring after another
Use the rammer to help press the braids into the recess
Figure 107: Installation of the braids
When installing the last ring, place the rammer in contact with the braids and
manually tighten the nuts.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 86 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
After completing this tightening phase, the control stem must turn without any
more effort than before installing the braids.
Gently tighten the rammer with a wrench until a slight resistance is felt when
operating the stem.
When pressurising the valve, if any leakage is observed, it is simply necessary to
tighten the rammer slightly.
The plaited braid must be cut in such a way as to obtain a
slight tightening effect on the outside diameter and an initial
play between the liner and the plaited braid.
To obtain this, wind the braid around the shaft liner (or around
a bar of the same diameter) to form a tight helix. (Take the
necessary precautions to avoid scoring the liner).
Example of a straight cut
Figure 108: Braid cutting
Example of an oblique cut
Experience has shown that an oblique cut is preferable to a straight cut. This makes it
easier to install the braid.
To obtain optimum sealing, it is necessary to tighten the rammer to between 2 and 5 times
the service pressure, depending on whether the fluid is a liquid or a gas.
It is essential to avoid jamming the rammer, so the braid must me tightened evenly and in
controlled manner.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 87 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
9.2. VALVE CALIBRATION
To obtain optimum operation of a regulation loop, it is essential to check the adjustment of
a valve and the other components that constitute a regulation loop (sensor-transmitter,
regulator and PID valve action).
9.2.1. Calibration of an I/P converter
The calibration of an I/P converter is quite simply the reverse of the adjustment of a
pressure transmitter.
Figure 109: Calibration of a regulating valve with I/P converter
To do this, we inject a 4-20 mA signal into the converter by means of a 4-20 mA current
generator (a tool which is very widely used by instrument engineers).
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 88 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
We then use a pressure gauge to check the output signal of the converter (0.2-1 bar). The
converter output signal must be linearly proportional to its input signal (4-20 mA).
If you see that the zero or the scale of the converter is offset, two adjusting screws are
provided for this purpose on an I/P converter.
IP Adjustments
Zero adjustment
Span adjustment
Mode selection
Lo-Hi span adjustment
Sensitivity adjustment
Item
1
2
3
4
5
IP port definitions
Input
Output
Exhaust
Conduit connection
Port size
¼" FNPT
¼" FNPT
½" FNPT
Item
A
B
C
D
Figure 110: Adjustments on a converter
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 89 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
You can also select the fail-safe state of the converter to be either high or low, by means
of the Mode switch. The same applies to the high or low scale, with the Lo-Hi Span
selection switch.
9.2.2. Calibration of an electro-pneumatic positioning device
Figure 111: Cross-sectional views of a MASONEILAN Model 8007
electro-pneumatic converter
9.2.2.1. Zero adjustment
Use a mercury column or a precision pressure gauge to check the output
pressure, a 4-20 mA generator to obtain constant current signal variations, and a
milliammeter connected to the terminals of the circuit to check the signal
variations between 4 and 20 mA,
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 90 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Connect the signal conductors. Connect the wires of the solenoid to the terminals
of the circuit board,
Adjust the signal you wish to inject using your 4-20 mA to 12 mA generator,
Adjust the supply pressure to 1.4 bars for a pneumatic output signal of
0.2 - 1 bar,
Turn the screw of the zero spring (52) to obtain the output value that corresponds
to a 12 mA input signal, i.e. up to 0.6 bars,
And finally, check the pneumatic output signal for 4 and 20 mA, which
corresponds to 0.2 bars and 1 bar.
If all the values are correct, you have finished the zero adjustment.
9.2.2.2. Adjustment of the scale
With the supply pressure adjusted to 1.4 bars, record the output pressure when
the electrical signal is it at its minimum value (4 mA),
Increase the electrical signal to its maximum value (20 mA) and record the output
pressure. A variation of the electrical signal for the min. and max (from 4 to
20 mA) should cause an output pressure variation of 0.8 bars if the scale is
0.2-1 bar,
If the pressure variation is different, pull clear the flapper (24) located at the rear
of the converter, remove the plug with an Allen wrench and then loosen and
unscrew the clamping screw by a few turns,
Turn the scale adjustment screw in either direction until the total variation of the
electrical signal causes the required total output pressure variation. To increase
the pressure variation amplitude, turn the adjustment screw clockwise. To reduce
the amplitude, turn the screw counter-clockwise,
Tighten the clamp screw.
Do not unscrew the scale adjustment screw excessively. The magnetic
force tends to decrease after one complete turn.
9.2.2.3. Replacement of the solenoid
Unscrew the screws (44) and (45) to release the solenoid (40) from the rocker,
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 91 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Lightly secure the new solenoid on the rocker with the screws (44) and (45); do
not tighten the screws. The stop screw (44) must not protrude beyond the inside
face of the solenoid,
Secure the rocker onto the magnet with the flexible strips and screws, and then
align the rocker according to the instructions provided in the following chapter.
9.2.2.4. Rocker alignment
Insert a 1/8" cylindrical pin in the alignment holes of the solenoid, the rocker and
the magnet, and place a shim with a height of 5/32" and a maximum width of
1 mm on the magnet, between the rocker and the solenoid.
Tighten the two bottom screws (42) of the inner flexible strip on the rocker, and
the two bottom screws of the outer flexible strip on the magnet.
Remove the flapper from the rocker. Reinstall the complete mechanism in the
case. Locate the zero spring support (39) and tighten the two screws (4).
Apply slight pressure on the rocker over the solenoid and adjust the stop screw
(44) until the rocker is parallel to the sealing faces of the case and cover. Whilst
maintaining the rocker in this position, tighten the other four screws of the flexible
strips,
Tighten the screw of the solenoid (45) and remove the alignment pins,
Reinstall the flapper,
and align and centre it
in the nozzle
Figure 112: Alignment of the
rocker
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 92 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
9.3. DEFECTIVE OPERATION OF THE I/P POSITIONING DEVICE
In case of anomaly of the I/P positioning device, there are two fundamental systems that
need to be checked:
The pneumatic system
The electrical system
9.3.1. Pneumatic system check
With a supply at 1.4 bars, check that the output signal drops to less than 0.1 bar
when the flapper is moved slightly away from the nozzle,
Apply a slight pressure on the flapper in order to close off the nozzle, and check
that the output signal reaches 1.4 bars,
If these results are not obtained, clean the calibrated orifice (59) by pressing its
unblocking device. Check the cleanness of the nozzle (16) and check that ball is
still in position. Check that the calibrated orifice (59) is correctly screwed into the
body of the controller. If the device continues to operate incorrectly, it will be
necessary to disassemble the controller,
If operation is irregular, check that there are no foreign particles lodged inside the
solenoid and the magnet.
9.3.2. Electrical system check
After checking the pneumatic system, it is necessary to check the electrical
system as follows, using an ohmmeter.
Disconnect the electrical signal conductors from the circuit card,
Connect the ohmmeter to the terminals of the converter circuit and check the
resistance of the circuit; you will find a small table giving the nominal value of the
resistance on the following page.
Disconnect one of the wires from the solenoid to the circuit card of the converter
and connect it to one of the wires of the ohmmeter. Connect the other wire of the
ohmmeter to the wire of the solenoid that is still connected. The measured value
of the resistance of the solenoid must correspond approximately to the value
given in the following table.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 93 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 113: Electrical circuit of the I/P positioning device
Signal
mA
Nominal resistance of circuit
Ω
Nominal resistance
of solenoid
Ω
TH
Ω
R
Ω
Colour code of
solenoid
4 - 20
216
173
82
91
Blue
Figure 114: Resistance value of Masoneilan solenoid
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 94 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
If the measured resistance of the solenoid is approximately correct, but if the total
resistance Th is not, replace the circuit card (15). If the measured resistance of
the solenoid is incorrect, replace the solenoid (40).
Connect one of the ohmmeter wires to the solenoid stop (44), and the other to the
disconnected wire of the solenoid in order to measure its insulance. If the
resistance indicated on the ohmmeter is not infinite, replace the solenoid.
9.3.3. Cleaning of the pneumatic system
9.3.3.1. Calibrated orifice
The calibrated orifice (59) is used for the passage of the air supply to the nozzle system. A
push-button, extended by a metal wire, enables the orifice to be unblocked if necessary.
The complete calibrated orifice assembly can be removed without disassembling the
controller.
9.3.3.2. Controller
21
53
54
55
56
59
65
Assembly screw
Assembly screw
Controller cover
Diaphragm
Intermediate plate
Calibrated orifice
O-ring
66
68
69
77
78
79
Controller body
Plug spring
Retaining plug
Diaphragm block
Exhaust plug
Inlet plug
Figure 115: Controller of the Masoneilan I/P positioning device
In case of failure, it is necessary to disassemble the unit for cleaning or replacement of
the deteriorated parts.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 95 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Disconnect the pneumatic system,
Remove the four screws securing the controller onto the body of the positioning
device. Separate the complete controller,
Remove the calibrated orifice and the spring retaining plug, and then remove the
plug and its spring,
Remove the six assembly screws in order to release the other components of the
controller,
Clean the parts with a clean soft cloth; if there are traces of oil or grease, use a
solvent (except on the diaphragm and the seals). Blow through the orifices and
ducts of this distributor valve (controller) with compressed air.
Reassembly
Insert two assembly screws into the two diametrically opposite holes in the
bottom of the controller,
Onto these parts, successively fit the diaphragm assembly, the intermediate
block and the seal,
Offer this assembly onto the body of the controller after introducing the spring of
the diaphragm into the latter. Check the correct installation and centring of all the
parts,
Insert and tighten the four assembly screws
Insert the plug and its spring. Tighten the spring retaining plug and also the
calibrated orifice,
Secure the controller onto the positioning device.
I recommend that you have the following spare parts available:
Solenoid
Circuit card
Complete controller with replacement diaphragm
Cam
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 96 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
9.4. MAINTENANCE OF SERVOMOTOR FOR ROTARY VALVE
Replacement of a rolling diaphragm
100
101
102
103
104
105
Yoke
Screw (2)
Washer (2)
Spring chamber
Spring
Diaphragm
106
107
108
110
111
111A
Screw (4)
Actuator cover
Piston
Washer
Nut
Nut
Figure 116: Detailed diagram of a MASONEILAN servomotor on a CAMFLEX II valve
To disassemble the diaphragm, it is necessary to:
Bypass the valve and close the manual shut-off valves,
Remove the four screws (106) and the cover (107),
Withdraw the diaphragm (105) and remove as much remaining adhesive as
possible from the piston (108). Use an acetone-based solvent if necessary.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 97 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
To reassemble the diaphragm, it is necessary to:
Apply a layer of Neoprene type
adhesive on the ridge and on the
inside face of the diaphragm base
(105), on the base of the piston in the
recess of the ridge at the entry to the
spring chamber (103),
Be careful not to allow any adhesive
to go beyond the limit that
corresponds to the flat section of the
piston base.
Figure 117: Limit of adhesive
Centre and press the diaphragm onto piston. Smear the outside face of the
diaphragm with talcum powder or grease,
Roll the diaphragm inside the spring chamber, until the ridge fits into its recess at
the entry to the spring chamber.
Gently and evenly press the ridge so that all the
adhesive-coated parts stick. Check that the
diaphragm rolled between the piston and the spring
chamber does not have any abnormal creases or
pinches in it.
Figure 118: Rolling the diaphragm
Move the cover (107) towards the spring chamber,
after correctly orienting the supply connection and
aligning the four tapped holes with the four plain
holes of the spring chamber. The ridge must be
pinched between the lip of the cover and that of the
spring chamber. Tighten the four screws (106).
Figure 119: Installation of the cover
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 98 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
10. TROUBLESHOOTING
10.1. CAVITATION AND VAPORISATION
10.1.1. Variation of the static pressure in a valve
In accordance with Bernoulli's theorem (refer to the course on Physical Measurements in
Instrumentation), the restriction of the passage area offered by the valve and its operator
causes an increase in the dynamic pressure.
This results in a decrease in the static pressure, the
magnitude of which will depend on:
The internal geometry of the valve;
The value of the static pressure downstream
of the valve.
This decrease in static pressure of the valve must be
compared to the vapour tension of the liquid at the
flow temperature, because this can lead to
phenomena that are detrimental to the quality of the
monitoring and to the durability of the equipment.
Figure 120: Variation of the static pressure in the
valve body
10.1.2. Cavitation
When the static pressure in the fluid path decreases and reaches the value of the vapour
tension of the liquid at the flow temperature, the cavitation phenomenon occurs (small
vapour bubbles form in the liquid, curve 2).
When the static pressure increases again (reduction of the velocity due to widening of the
fluid path), the vapour bubbles condense and implode.
This cavitation phenomenon has the following disadvantages:
Noise, at an unacceptable sound level, which is very characteristic because it
sounds like pebbles flowing through the pipe;
High-frequency vibrations which cause all the hardware of the valve and its
accessories to work loose;
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 99 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Rapid destruction of the plug, the seat and the body, by removal of metal
particles. The surfaces that are subjected to the cavitation phenomena have a
grainy surface;
The flow through the valve is no longer
proportional to the command.
Valves with a lot of internal profiling have an increased
tendency to cavitate.
Figure 121: Example of damage caused by cavitation
10.1.3. Vaporisation
If the static pressure downstream of the valve is low (high pressure differential in the
valve), the gas bubble implosion process does not occur: the bubbles remain present in
the fluid path, which results in the vaporisation phenomenon (curve 3).
This vaporisation phenomenon has the following disadvantages:
Noise, although the sound level is not as high as that caused by cavitation;
Mechanical damage to the plug, the seat and the body, due to the high-velocity
flow of a gas and liquid mixture.
The surfaces exposed to this phenomenon have cavities with a polished
appearance;
Critical operating conditions.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 100 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11. VALVE SIZING
11.1. THE Cv AND THE Kv of a VALVE
11.1.1. What is the Cv of a valve?
The flow coefficient Cv, used for the first time by Masoneilan in 1944, rapidly became the
universal reference for measuring the flow of fluid through a valve. This is because this
coefficient is so practical that it is now almost always used in calculations for the sizing of
valves or to determine the flow-rates passing through them.
As the basic idea to state the flow capabilities of a valve under precise conditions is of
American origin, some manufacturers give the water flow-rate in "gallons per minute" with
a ∆P of 1 PSI (valve fully open).
This specific flow-rate is called: The Cv of the valve (Flow coefficient of the valve).
Manufacturer calculation manuals state the methods for calculating the Cv, for liquids,
gases and vapours, under the most varied conditions.
These, and more generally the calculations used in valve sizing and adjustment, are often
very complex.
The Cv of a valve is therefore expressed using the following American formula:
Cv = Q
d
ΔP
Where:
Q: flow-rate in US gallons per minute
d: density (with respect to water)
ΔP: pressure differential en psi
Note:
1 US gallon = 3.758 litres
1 PSI = 0.069 bars or 69 hPa
The Cv is a size reference that the technician can use to quickly and accurately determine
the size of a restriction based on known values of the flow-rate, the pressure, and any
other associated parameters; this is furthermore applicable to any fluid. The Cv is
proportional to the passage area between the seat and the plug.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 101 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Cv = 0 when the valve is closed;
Cv = Cv_ {max} when the valve is fully open.
The Cv also depends on the internal profile of the valve, and on the type of flow in the
valve.
Figure 122: Profile of a direct flow valve body with a high Cv
Figure 123: Profile of an indirect flow valve body with a low Cv
11.1.2. What is the Kv of a valve?
For us technicians, it is actually easier to work with ∆P values in bars and flow-rates in
m3/h.
So the flow factor or Kv is the Cv of a valve, except that we use metric units.
Kv = 1.16 / Cv
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 102 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11.1.3. Standard formulae for calculation of a valve Cv
For liquids:
Q: flow-rate in m3/h
D: density
ΔP: pressure differential in bars
For gases: Cv =
Q
d .T
295 ΔP(P1 + P2 )
Q: flow-rate in Nm3/h (1013 mb and 15.6 °C)
D: gas density under standard conditions, calculated with respect to that of the air, taken to
be = 1
T: absolute temperature in degrees Kelvin
P1: upstream pressure in bars abs.
P2: downstream pressure in bars abs.
ΔP: P1 - P2 in bars
Note:
The formulae mentioned above are for non-critical flows.
11.1.4. Cv calculation formulae according to the manufacturer Masoneilan
11.1.4.1. For liquids in imperial units
Non-critical flow:
Critical flow (cavitation or vaporisation):
ΔP < C f (ΔPs )
ΔP ≥ C f (ΔPs )
2
2
Volumetric flow:
Cv = q
Gf
Cv =
ΔP
Gf
q
Cf
ΔPs
Mass flow:
Cv =
W
Cv =
500 G f ΔP
W
500C f G f ΔPs
⎛
P ⎞
ΔPs = P1 − ⎜⎜ 0,96 − 0,287 V ⎟⎟ PV
PC ⎠
⎝
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 103 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
But as a simplification, if PV < 0.5 P1; ΔPS = P1 - PV
CV: Flow coefficient
Cf: Pressure recovery factor from the liquid in a regulating valve without adjacent unions
Gf: Density at the temperature of the flow, calculated with respect to water (1 at 60 °F)
P1: Absolute upstream pressure (psia)
P2: Absolute downstream pressure (psia)
PC: Absolute critical thermodynamic pressure (psia)
PV: Vapour tension of the liquid at the upstream temperature (psia)
ΔP: Pressure differential P1 – P2 (psi)
q: Volumetric flow of the liquid (USgal/min)
W: Mass flow of the liquid (lbs/hr)
11.1.4.2. For liquids in metric units
Non-critical flow:
Critical flow (cavitation or vaporisation):
ΔP < C f (ΔPs )
ΔP ≥ C f (ΔPs )
2
2
Volumetric flow:
Cv = 1,16q
Gf
ΔP
Cv =
1,16q G f
Cf
ΔPs
Cv =
1,16W
C f G f ΔPs
Mass flow:
Cv =
1,16W
G f ΔP
⎛
P ⎞
ΔPs = P1 − ⎜ 0,96 − 0,287 V ⎟ PV
⎜
PC ⎟⎠
⎝
But as a simplification, if PV < 0.5 P1; ΔPS = P1 - PV
CV: Flow coefficient
Cf: Pressure recovery factor from the liquid in a regulating valve without adjacent unions
Gf: Density at the temperature of the flow, calculated with respect to water (1 at 15.6 °C
P1: Absolute upstream pressure (bars abs)
P2: Absolute downstream pressure (bars abs)
PC: Absolute critical thermodynamic pressure (bars abs)
PV: Vapour tension of the liquid at the upstream temperature (bars abs)
ΔP: Pressure differential P1 – P2 (bar)
q: Volumetric flow of the liquid (m³/h)
W: Mass flow of the liquid (t/h)
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 104 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11.1.4.3. For gases and steam, in imperial units
Volumetric flow for gas: CV =
Mass flow for gas: CV =
Saturated steam: CV =
Q GTZ
834C f P1 y − 0.148 y 3
(
W Z
2.8C f P1 G f y − 0.148 y 3
(
W
1.83C f P1 y − 0.148 y 3
Superheated steam: CV =
(
)
)
W (1 + 0.0007Tsh )
1.83C f P1 y − 0.148 y 3
(
)
)
Where, for 77000 valves, LO-DB cartridges and relief plates, and for two-stage 41000
1.40 ΔP
valves and 72000 valves: y =
Cf
P1
Where, for all other valves: y =
1.36 ΔP
(maximum value = 1.50, at this value
Cf
P1
y - 0.148 y³ = 1.0)
CV: Flow coefficient
Cf: Pressure recovery factor from the liquid in a regulating valve without adjacent unions
G: Gas density at 60 °F (air = 1.0)
Gf: Density at the temperature of the flow (= G x 520 / T)
P1: Absolute upstream pressure (psia)
P2: Absolute downstream pressure (psia)
ΔP: Pressure differential P1 – P2 (psi)
Q: Volumetric flow at 14,7 psia and 60 °F (scfh)
T: Temperature of the flow (°R)
Tsh: Steam overtemperature (°F)
W: Mass flow (lbs/hr)
Z: Compressibility factor
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 105 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11.1.4.4. For gases and steam in metric units
Volumetric flow for gas: CV =
Mass flow pour gas: CV =
Saturated steam: CV =
Q GTZ
257C f P1 y − 0.148 y 3
(
54.5W Z
C f P1 G f y − 0.148 y 3
(
83.7W
C f P1 y − 0.148 y 3
Superheated steam: CV =
(
)
)
)
83.7(1 + 0.00126Tsh )W
C f P1 y − 0.148 y 3
(
)
Where, for 77000 valves, LO-DB cartridges and relief plates, and for two-stage 41000
1.40 ΔP
valves and 72000 valves: y =
Cf
P1
Where, for all other valves: y =
1.36 ΔP
(maximum value = 1.50, at this value
Cf
P1
y - 0.148 y³ = 1.0)
CV: Flow coefficient
Cf: Pressure recovery factor from the liquid in a regulating valve without adjacent unions
G: Gas density at 15,6 °C (air = 1.0)
Gf: Density at the temperature of the flow (= G x 288 / T)
P1: Absolute upstream pressure (bar abs)
P2: Absolute downstream pressure (bar abs)
ΔP: Pressure differential P1 – P2 (bar)
Q: Volumetric flow at 1013 mbar abs and 15 °C (m³/h)
T: Temperature of the flow (K)
Tsh: Steam overtemperature (°C)
W: Mass flow (t/h)
Z: Compressibility factor
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 106 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11.1.5. Cv calculation for a valve
11.1.5.1. Equivalent Cv with 2 valves in parallel
Qeq = Q1 + Q2
∆Peq = ∆P1 = ∆P2
11.1.5.2. Equivalent Cv with 2 valves in series
Qeq = Q1 = Q2
∆Peq = ∆P1 + ∆P2
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 107 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11.2. CHOICE OF VALVE
After calculating the Cv, the choice of valve from the manufacturer's catalogue can lead to
a valve with a diameter less than that of the pipe. In this case, the valve is installed
between convergent and divergent pipe sections.
Figure 124: Valve between convergent and divergent pipe sections
This creates an additional pressure differential, which must be taken into account in the
calculation of the valve.
This option is used if there is no other choice, but it is usually recommended to do
everything possible to choose a valve whose diameter is identical to that of the pipe.
It is also necessary to take the material of the pipe into account, and to choose a valve
made of the same material (e.g. Stainless Steel 316, Carbon steel, etc.).
The process conditions will enable you to choose the type of valve body.
The safety conditions will enable you to know the fail-safe position of the valve (FAIL
CLOSED or FAIL OPEN) and whether or not you add limit switches to it.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 108 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
12. TAG AND IDENTIFICATION OF VALVES
12.1. ALL-OR-NOTHING VALVES
12.1.1. Blow Down Valve
BDVs: Blow Down Valves. Safety level ESD, GSSD
These are valves which have an emergency decompression function, releasing the fluid to
the torch of the installations.
They are necessarily of the FAIL OPEN type.
They are mainly used on compressors, on VHP reservoirs and on gas treatment units.
12.1.2. Emergency Shut-Down Valve
ESDVs: Emergency Shut-Down Valves. Safety level ESD, GSSD.
These valves have a safety shut-off function.
They protect against overpressure and pipe bursting, and are used to shut-off platforms in
cases of ESD or GSSD.
These valves are present in the safety process panels, and are ordered to close when the
bar is tripped.
These valves are reopened locally - on a pneumatic or hydraulic cabinet -, once the
console operator has identified the fault, reset the safety process panel and given the
authorisation to reopen from the console.
They are necessarily of the FAIL CLOSED type. They are often two-way valves with an air
reserve.
They are mainly used on oil and gas outlets / inlets.
12.1.3. Remote Operated Valve
ROVs: Remote Operated Valves
These are controlled by the operator from the control console.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 109 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
They do not have a shut-off function, and they are not present on the safety process
panels.
Their fail-safe position is not necessarily defined.
These are fluid routing valves, and are mainly used on the production / test manifolds of
wells, on pump discharges and on chemical line selectors.
12.1.4. Shut-Down Valve
SDVs: Shut-Down Valves. Safety level PPSD, EPSD and higher, sometimes TPSD
These valves have a safety shut-off function. They are present on the safety process
panels and are ordered to close when the bar trips. (Note that some SDVs can be closed
by the operating personnel in case of TPSD).
These valves are then reopened from the console*, once the operator has identified the
fault and reset the safety process panel.
These valves are mainly found on the inlets / outlets of reservoirs and on machine intakes.
These valves are of the FAIL CLOSED type (except for the test separator bypass valve,
which is of the FO type).
12.1.5. Surface Safety Valve
SSVs: Surface Safety Valves.
Safety level PPSD, EPSD and higher, TPSD
These are SDV type valves on well-head tubings, and are also called master valves.
12.1.6. Surface Controlled Sub-Surface Safety Valve
SCSSVs: Surface Controlled Sub-Surface Safety Valves. Safety level ESD, GSSD
These are ESDV type valves on well-bottom tubings, and are also called bottom valves.
They are controlled from the surface by high pressure hydraulic lines (up to 500 bars), in
order not to remain blocked open by the pressure of the deposit in case of leakage.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 110 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
12.2. REGULATING VALVES
RCV: Remote Control Valve,
HCV: Hand control valve.
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 111 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
13. APPENDICES
Lengths
mm
0.10
cm
inches
25.40
mm
mm
0.001
m
inches
2.54
cm
mm
0.039
inches
inches
0.0254
m
mm
0.00328
feet
inches
0.0833
feet
cm
10.0
mm
feet
304.8
mm
cm
0.010
m
feet
30.48
cm
cm
0.394
inches
feet
0.304
m
cm
0.0328
feet
feet
12.0
inches
mm²
0.010
cm²
sq. inches
645.2
mm²
mm²
10-6
m²
sq. inches
6.452
cm²
mm²
0.00155
sq. inches
sq. inches
0.000645
m²
mm²
1.076 10-5
sq. feet
sq. inches
0.00694
sq. feet
cm²
100
mm²
sq. feet
9.29 104
mm²
cm²
0.0001
m²
sq. feet
929
cm²
cm²
0.155
sq. inches
sq. feet
0.0929
m²
cm²
0.001076
sq. feet
sq. feet
144
sq. inches
us gall / min GPM
3.785
l / min
cubic feet / hr
0.1247
gpm
us gallons / min
0.133
cubic feet / min
cubic feet / hr
0.472
l / min
us gallons / min
8.021
cubic feet / hr
cubic feet / hr
0.01667
cubic feet / min
us gallons / min
0.227
m³ / h
cubic feet / hr
0.0283
m³ / h
us gallons / min
34.29
barrels / day
m³ / h
4.403
GPM
cubic feet / min
7.481
GPM
m³ / h
16.67
l / min
cubic feet / min
28.32
l / min
m³ / h
0.5886
cubic feet / min
cubic feet / min
60.0
cubic feet / hr
m³ / h
35.31
cubic feet / hr
cubic feet / min
1.699
m³ / h
m³ / h
150.9
barrels / day
cubic feet / min
256.5
barrels / day
Surfaces
Flow-rates
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 112 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Speeds
feet / sec
60
feet / min
m/s
3.280
feet/sec
feet / sec
0.3048
m/s
m/s
196.9
feet / min
feet / sec
1.097
km / hr
m/s
3.6
km / h
feet / sec
0.6818
miles / hr
m/s
2.237
miles / hr
pounds
0.0005
short ton
kg
2.205
pounds
pounds
0.000446
long ton
kg
0.0011
short ton
pounds
0.453
kg
kg
0.00098
long ton
pounds
0.000453
t
kg
0.001
t
short ton
2 000
pounds
t
2 205
pounds
short ton
0.8929
long ton
t
1.102
short ton
short ton
907.2
kg
t
0.984
long ton
short ton
0.9072
t
t
1 000
kg
long ton
2 240
pounds
long ton
1.120
short ton
long ton
1 016
kg
long ton
1.016
t
Masses
Volume and capacity
cm³
0.06102
cubic inches
l
1 000
cm³
cm³
3.531 10-5
cubic feet
l
61.02
cubic inches
cm³
10-6
m³
l
0.03531
cubic feet
cm³
0.0001
l
l
0.001
m³
us gallons
l
0.264
gallons
cm³
gallons
3 785
cm³
cm³
-4
2.642 10
6
m³
10
m³
61 023
cubic inches
gallons
231
cubic inches
m³
35.31
cubic feet
gallons
0.1337
cubic feet
m³
1 000
l
gallons
3 785 10-3
m³
m³
264.2
gallons
gallons
3.785
l
cubic feet
28 320
cm³
cubic feet
1 728
cubic inches
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 113 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
cubic feet
0.0283
m³
cubic feet
28.32
l
cubic feet
7.4805
gallons
Pressure and hauteur
pounds / sq.inch
0.06895
bar
kg / cm²
14.22
psi
pounds / sq.inch
0.06804
atmosphere
kg / cm²
0.9807
bar
pounds / sq.inch
0.0703
kg / cm²
kg / cm²
0.9678
atmosphere
pounds / sq.inch
6.895
kPa
kg / cm²
98.07
kPa
pounds / sq.inch
2.307
ft de H2O (4 °c)
kg / cm²
32.81
ft de H2O (4 °c)
pounds / sq.inch
0.703
m de H2O (4 °c)
kg / cm²
10
m de H2O (4 °c)
pounds / sq.inch
5.171
Cm de Hg (0 °c)
kg / cm²
73.56
cm Hg
pounds / sq.inch
51.71
torr (mm Hg 0 °c)
kg / cm²
735.6
torr (mm Hg)
pounds / sq.inch
2.036
inch hg (0 °c)
kg / cm²
28.96
inch Hg
atmosphere
14.69
psi
kPa
0.145
psi
atmosphere
1.013
bar
kPa
0.01
bar
atmosphere
1.033
Kg / cm²
kPa
0.00986
atmosphere
atmosphere
101.3
kPa
kPa
0.0102
kg / cm²
atmosphere
33.9
ft de H2O
kPa
0.334
ft H2O
atmosphere
10.33
m de H2O
kPa
0.102
m H2O
atmosphere
76.00
cm de Hg
kPa
0.7501
cm Hg
atmosphere
760.0
torr (mm Hg)
kPa
7.501
torr (mm Hg)
atmosphere
29.92
inch Hg
kPa
0.295
inch Hg
bar
14.50
psi
mbar
0.001
bar
bar
0.9869
atmosphere
bar
1.020
kg / cm²
bar
100
kPa
bar
33.45
ft de H2O
bar
10.20
m de H2O
bar
75.01
cm Hg
bar
750.1
torr (mm Hg)
bar
29.53
inch Hg
Table 10: Conversion of units
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 114 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
13.1. CRITICAL CONSTANTS OF CERTAIN LIQUID AND GAS BODIES
Critical pressure - PC
Critical temperature - TC
Designation
k * CP / CV
psia
Bars abs
°F
°C
Acetic acid
CH3-CO-OH
841
58.0
612
322
Acetone
CH3-CO-CH3
691
47.6
455
235
Acetylene
C2H2
911
62.9
97
36
1.26
Air
O2+N2
547
37.8
-222
-141
1.40
Ammonia
NH3
1638
113.0
270
132
1.33
Argon
A
705
48.6
-188
-122
1.67
Benzene
C6H6
701
48.4
552
289
1.12
Butane
C4H10
529
36.5
307
153
1.09
Carbon dioxide
CO2
1072
74.0
88
31
1.30
Carbon monoxide
CO
514
35.5
-218
-139
1.40
Carbon tetrachloride
CCl4
661
45.6
541
283
Chlorine
Cl2
1118
77.0
291
144
1.36
Ethane
C2H6
717
49.5
90
32
1.22
Ethyl alcohol
C2H5OH
927
64.0
469
243
1.13
Ethylene
Ch2=CH2
742
51.2
50
10
1.26
Ether
C2H5-O-C2H5
522
36.0
383
195
Fluorine
F2
367
25.3
-247
-155
1.36
Helium
He
33.2
2.29
-450
-268
1.66
Heptane
C7H16
394
27.2
513
267
Hydrogen
H2
188
13.0
-400
-240
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
4.15
1.41
Page 115 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Critical pressure - PC
Critical temperature - TC
Designation
k * CP / CV
psia
Bars abs
°F
°C
Hydrochloric acid
HCl
1199
82.6
124
51
1.41
Isobutane
(CH3)CH-CH3
544
37.5
273
134
1.10
Isopropyl alcohol
CH3-CHOH-CH3
779
53.7
455
235
Methane
CH4
673
46.4
-117
-83
1.31
Methyl alcohol
H-CH2OH
1156
79.6
464
240
1.20
Nitrogen
N2
492
34.0
-233
-147
1.40
Nitrous oxide
N2O
1054
72.7
99
37
1.30
Octane
CH-(CH2)6-CH3
362
25.0
565
296
1.05
Oxygen
O2
730
50.4
-182
-119
1.40
Pentane
C5H12
485
33.5
387
197
1.07
Phenol
C6H5OH
889
61.3
786
419
Phosgene
COCl2
723
56.7
360
182
Propane
C3H8
617
42.6
207
97
1.13
Propylene
CH2=CH-CH3
661
45.6
198
92
1.15
Refrigerant 12
CCl2F2
582
40.1
234
112
1.14
Refrigerant 22
CHClF2
713
49.2
207
97
1.18
Sulphur dioxide
SO2
1142
78.8
315
157
1.29
Water
H2O
3206
221.0
705
374
1.32
Table 11: Critical pressure and critical temperature of a few selected materials
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 116 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Designation
Mass volume – lb/ft³
14.7 psia and 60 °F
Masse volume – kg/m³
1013 mbar and 15,6 °C
Liquid
Liquid
Gas
Gas
Molar mass
g/mol
Acetic acid
CH3-CO-OH
65.7
1052.4
66.1
Acetone
CH3-CO-CH3
49.4
791.3
58.1
Acetylene
C2H2
0.069
1.11
26.0
Air
O2+N2
0.0764
1.223
29.0
Ammonia
NH3
0.045
0.72
17.0
Argon
A
0.105
1.68
39.9
Benzene
C6H6
54.6
874.5
78.1
Butane
C4H10
0.154
2.47
58.1
Carbon dioxide
CO2
0.117
1.87
44.0
Carbon monoxide
CO
0.074
1.19
28.0
Carbon tetrachloride
CCl4
99.5
1593.9
153.8
Chlorine
Cl2
0.190
3.04
70.9
Ethane
C2H6
0.080
1.28
30.1
Ethyl alcohol
C2H5OH
49.52
Ethylene
Ch2=CH2
Ether
C2H5-O-C2H5
793.3
0.074
44.9
46.1
1.19
719.3
28.1
74.1
Fluorine
F2
0.097
1.55
38.0
Helium
He
0.011
0.18
4.0
Heptane
C7H16
Hydrogen
H2
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
42.6
682.4
0.005
100.2
0.08
2.02
Page 117 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Designation
Mass volume – lb/ft³
14.7 psia and 60 °F
Masse volume – kg/m³
1013 mbar and 15,6 °C
Liquid
Liquid
Gas
Molar mass
g/mol
Gas
Hydrochloric acid
HCl
0.097
1.55
36.5
Isobutane
(CH3)CH-CH3
0.154
2.47
58.1
Isopropyl alcohol
CH3-CHOH-CH3
49.23
Methane
CH4
Methyl alcohol
H-CH2OH
788.6
0.042
49.66
60.1
0.67
16.0
795.5
32.0
Nitrogen
N2
0.074
1.19
28.0
Nitrous oxide
N2O
0.117
1.87
44.0
Octane
CH-(CH2)6-CH3
43.8
Oxygen
O2
701.6
0.084
114.2
1.35
32.0
Pentane
C5H12
38.9
623.1
72.2
Phenol
C6H5OH
66.5
1065.3
94.1
Phosgene
COCl2
0.108
1.73
98.9
Propane
C3H8
0.117
1.87
44.1
Propylene
CH2=CH-CH3
0.111
1.78
42.1
Refrigerant 12
CCl2F2
0.320
5.13
120.9
Refrigerant 22
CHClF2
0.228
3.65
86.5
Sulphur dioxide
SO2
0.173
2.77
64.1
Water
H2O
62.34
998.6
18.0
Table 12: Mass volume and molar masse of a few selected materials
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 118 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
14. EXERCISES
1. Which item is the Packing gland rammer?
‰ Item 5
‰ Item 6
‰ Item 7
2
1
2. Which item is the plug?
‰ Item 1
5
6
‰ Item 4
‰ Item 8
3
4
7
8
9
3. Which item is the seat?
‰ Item 9
10
‰ Item 3
‰ Item 2
4. The servomotor of this valve is:
‰ Rotary
‰ Linear
5. One of the major hazards for a valve is?
‰ Gravitation
‰ Pressure differential
‰ Cavitation
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 119 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
6. An All-or-Nothing valve consists of:
‰ A positioning device
‰ A one-way or two-way actuator
‰ An electrovalve
‰ An I/P converter
7. The supply pressure of a regulating valve is:
‰ 7 bars
‰ 3 PSI
‰ 1.4 bars or 2.1 bars
8. What is the purpose of an electro-pneumatic positioning device?
‰ To convert an electrical signal (4-20 mA) into a pneumatic signal (0.2 - 1 bar)
‰ To position the regulating valve
‰ Both
9. A rolling diaphragm type servomotor is designed for:
‰ A linear valve
‰ A piston valve
‰ A rotary valve
10. A servomotor is said to be "reverse" when:
‰ The air enters above the diaphragm cover
‰ The air enters beneath the diaphragm cover
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 120 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11. In the body of this valve, the fluid:
‰ Tends to close it
‰ Tends to open it
‰ Is direct
12. Which of these two servomotors is direct?
‰ The one on the right
‰ The one on the left
‰ Both
13. I am in the following situation: I have a direct
action valve body and a reverse servomotor:
What will the fail-safe position of my
regulating valve be?
‰ Fail Open
‰ Fail Closed
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 121 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
15. FIGURES
Figure 1: Location of the "regulating valve" in the regulation loop .......................................7
Figure 2: Technology of a regulating valve ........................................................................10
Figure 3: The two assemblies of a regulating valve ...........................................................11
Figure 4: Linear flow characteristic ....................................................................................13
Figure 5: Equal percentage flow characteristic ..................................................................13
Figure 6: Quick opening flow characteristic .......................................................................14
Figure 7: Fluid displacement in a single-seat body ............................................................15
Figure 8: Single-seat body .................................................................................................16
Figure 9: Double-seat body................................................................................................17
Figure 10: Fluid displacement in a double-seat body.........................................................18
Figure 11: Cage valve........................................................................................................19
Figure 12: 3-way mixing valve ...........................................................................................21
Figure 13: 3-way bypass valve ..........................................................................................22
Figure 14: Diaphragm valve...............................................................................................23
Figure 15: Functional diagram of the diaphragm valve ......................................................23
Figure 16: Guillotine valve .................................................................................................24
Figure 17: Micro-flow control valve with adjustable valve coefficient (Varipak)..................25
Figure 18: Example of a micro-flow valve ..........................................................................26
Figure 19: Adjustment of the Cv ........................................................................................26
Figure 20: Butterfly valve ...................................................................................................27
Figure 21: Ball valve ..........................................................................................................28
Figure 22: Example of a ball valve.....................................................................................29
Figure 23: Valve with eccentric spherical shutter...............................................................30
Figure 24: Cross-sectional view of the eccentric spherical shutter ....................................31
Figure 25: Functional diagram of the eccentric spherical shutter valve .............................31
Figure 26: Different plugs and their flow characteristics ....................................................33
Figure 27: Quick opening plug ...........................................................................................34
Figure 28: Linear plug ........................................................................................................34
Figure 29: Modified linear plug...........................................................................................34
Figure 30: Equal percentage plug......................................................................................35
Figure 31: Equal percentage plug turned with a Vee-shaped aperture..............................35
Figure 32: Parabolic plug ...................................................................................................35
Figure 33: Quick opening cage ..........................................................................................36
Figure 34: Linear cage .......................................................................................................36
Figure 35: Equal percentage cage.....................................................................................37
Figure 36: Low noise cage.................................................................................................37
Figure 37: Diagram of valve cap ........................................................................................38
Figure 38: Packing gland of a valve...................................................................................39
Figure 39: Sealing boot......................................................................................................39
Figure 40: Graphite and PTFE packing rings.....................................................................40
Figure 41: Examples of graphite and PTFE braids ............................................................40
Figure 42: Poor sealing, leakage from the packing gland ..................................................41
Figure 43: Diaphragm type servomotor..............................................................................43
Figure 44: Simplified diagram of a diaphragm type servomotor.........................................45
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 122 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 45: Cross-sectional view of a servomotor with multiple return springs....................46
Figure 46: Rolling diaphragm type servomotor ..................................................................46
Figure 47: Piston type servomotor .....................................................................................47
Figure 48: Simplified diagram of a one-way piston type servomotor for a linear valve ......48
Figure 49: Two-way piston type servomotor for a rotary valve...........................................48
Figure 50: Hydraulic servomotor........................................................................................49
Figure 51: Functional diagram of the control of a hydraulic servomotor ............................50
Figure 52: Electric servomotor with motor and gearbox.....................................................51
Figure 53: Example of an electric servomotor....................................................................52
Figure 54: Valve with solenoid type servomotor ................................................................52
Figure 55: Example of a solenoid type servomotor............................................................52
Figure 56: Direct action valve body....................................................................................53
Figure 57: Reverse action valve body................................................................................53
Figure 58: Direct action servomotor ...................................................................................54
Figure 59: Reverse action servomotor ...............................................................................54
Figure 60: Valve fail-safe position......................................................................................55
Figure 61: Different possibilities for the fail-safe position of a valve...................................56
Figure 62: Functional diagram of pneumatic positioning device ........................................59
Figure 63: Masoneilan pneumatic positioning device ........................................................60
Figure 64: View of the cam with and its reaction spring .....................................................60
Figure 65: MASONEILAN lever orientation and cam position............................................61
Figure 66: Nozzle-flapper system with electromagnet on I/P positioning device................62
Figure 67: Functional diagram of electro-pneumatic positioning device ............................63
Figure 68: MASONEILAN type 8013 electro-pneumatic positioning device.......................64
Figure 69: Direct action: beneath the rocker ......................................................................64
Figure 70: Reverse action: above the rocker ....................................................................64
Figure 71: Solenoid wire reversal to change the direction of action of the positioning device
...................................................................................................................................64
Figure 72: Functional diagram of intelligent positioning device..........................................66
Figure 73: ABB model TZID-C intelligent positioning device installed on a linear valve ....67
Figure 74: ABB model TZID-C intelligent positioning device..............................................68
Figure 75: MASONEILAN I/P converter .............................................................................69
Figure 76: Lubricator on packing gland cap .......................................................................70
Figure 77: Microswitch on regulating valve ........................................................................71
Figure 78: Proximity sensor ...............................................................................................71
Figure 79: Position of microswitch on a linear valve ..........................................................72
Figure 80: Position of the microswitch on a rotary valve ....................................................73
Figure 81: Functional diagram of an inductive sensor .......................................................73
Figure 82: Functional diagram of a capacitive sensor........................................................74
Figure 83: Functional diagram of a Booster .......................................................................75
Figure 84: Example of a "‘booster" ....................................................................................75
Figure 85: Control signal higher than the output ................................................................75
Figure 86: Output higher than control signal ......................................................................76
Figure 87: Functional diagram of the distributor valve on an actuator ...............................77
Figure 88: Displacement of the slide valve in a distributor valve........................................78
Figure 89: Displacement of the actuator piston as a function of the displacement of the
slide valve in the 4/2 distributor valve .........................................................................78
Figure 90: Schematic representation of a 4/2 distributor valve ..........................................79
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 123 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Figure 91: Schematic diagram of a 3/2 distributor valve ....................................................79
Figure 92: Schematic diagram of a 5/2 distributor valve ....................................................79
Figure 93: Schematic diagram of a 5/2 distributor valve ....................................................80
Figure 94: Schematic diagrams of distributor valve control methods.................................80
Figure 95: Diagram of a monostable distributor valve with pneumatic control ...................81
Figure 96: Example of a monostable distributor valve with electrical control .....................81
Figure 97: Diagram of a bistable distributor valve with pneumatic control .........................81
Figure 98: Example of a bistable distributor valve with electrical control ...........................81
Figure 99: Example of distributor valves mounted on the base .........................................82
Figure 100: Example of a base for a pneumatic distributor valve ......................................82
Figure 101: Example of a base for a pneumatic distributor valves mounted on a DIN rail in
a cabinet .....................................................................................................................82
Figure 102: Example of distributor valves which fit directly onto the valve, without the need
for a base....................................................................................................................82
Figure 103: Examples of various solenoids .......................................................................83
Figure 104: Connectors used for the electrical connection of the solenoid ........................83
Figure 105: Manual control installed on the top of the servomotor ....................................85
Figure 106: Manual control installed on the side of the servomotor...................................85
Figure 107: Installation of the braids..................................................................................86
Figure 108: Braid cutting....................................................................................................87
Figure 109: Calibration of a regulating valve with I/P converter .........................................88
Figure 110: Adjustments on a converter ............................................................................89
Figure 111: Cross-sectional views of a MASONEILAN Model 8007 electro-pneumatic
converter.....................................................................................................................90
Figure 112: Alignment of the rocker...................................................................................92
Figure 113: Electrical circuit of the I/P positioning device ..................................................94
Figure 114: Resistance value of Masoneilan solenoid.......................................................94
Figure 115: Controller of the Masoneilan I/P positioning device ........................................95
Figure 116: Detailed diagram of a MASONEILAN servomotor on a CAMFLEX II valve ....97
Figure 117: Limit of adhesive.............................................................................................98
Figure 118: Rolling the diaphragm.....................................................................................98
Figure 119: Installation of the cover...................................................................................98
Figure 120: Variation of the static pressure in the valve body............................................99
Figure 121: Example of damage caused by cavitation ....................................................100
Figure 122: Profile of a direct flow valve body with a high Cv ..........................................102
Figure 123: Profile of an indirect flow valve body with a low Cv.......................................102
Figure 124: Valve between convergent and divergent pipe sections ...............................108
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 124 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 125 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
16. TABLES
Table 1: Advantages and Disadvantages of the single seat ..............................................15
Table 2: Advantages and Disadvantages of the double seat .............................................18
Table 3: Advantages and Disadvantages of the cage valve ..............................................20
Table 4: Advantages and Disadvantages of the diaphragm valve .....................................24
Table 5: Advantages and Disadvantages of the guillotine valve ........................................24
Table 6: Advantages and Disadvantages of the butterfly valve .........................................27
Table 7: Advantages and Disadvantages of the ball valve ................................................29
Table 8: Advantages and Disadvantages of the eccentric shutter valve............................32
Table 9: Combinations of valve fail-safe and positioning device positions.........................56
Table 10: Conversion of units ..........................................................................................114
Table 11: Critical pressure and critical temperature of a few selected materials .............116
Table 12: Mass volume and molar masse of a few selected materials ............................118
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 126 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
17. ANSWERS TO THE EXERCISES
1. Which item is the rammer de Packing gland?
‰ Item 5
; Item 6
‰ Item 7
2
1
2. Which item is the plug?
‰ Item 1
5
6
‰ Item 4
; Item 8
3
4
7
8
9
3. Which item is the seat?
; Item 9
10
‰ Item 3
‰ Item 2
4. The servomotor of this valve is:
‰ Rotary
; Linear
5. One of the major hazards for a valve is?
‰ Gravitation
‰ Pressure differential
; Cavitation
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 127 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
6. An All-or-Nothing valve consists of:
‰ A positioning device
; A one-way or two-way actuator
; Un electrovalve
‰ An I/P converter
7. The supply pressure of a regulating valve is:
‰ 7 bars
‰ 3 PSI
; 1.4 bars or 2.1 bars
8. What is the purpose of an electro-pneumatic positioning device?
‰ To convert an electrical signal (4-20 mA) into a pneumatic signal (0.2 - 1 bar)
‰ To position the regulating valve
; Both
9. A rolling diaphragm type servomotor is designed for:
‰ A linear valve
‰ A piston valve
; A rotary valve
10. A servomotor is said to be "reverse" when:
‰ The air enters above the diaphragm cover
; The air enters beneath the diaphragm cover
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 128 / 129
Field Operations Training
Instrumentation Maintenance
Valves and Actuators
11. In the body of this valve, the fluid:
‰ Tends to close it
; Tends to open it
‰ Is direct
12. Which of these two servomotors is direct?
‰ The one on the right
; The one on the left
‰ Both
13. I am in the following situation: I have a direct
action valve body and a reverse servomotor:
What will the fail-safe position of my
regulating valve be?
‰ Fail Open
; Fail Closed
Training Manual: EXP-MN-SI040-EN
Last Revised: 09/04/2008
Page 129 / 129