Control Valve
Instrument Training Material
Control Valve

Final Control Element
Most widely used

Other types of final control elements are
Dampers or louvers
Variable pitch fan blades
Final Control Element


Final Control Element
Considered as the muscle of
automatic control.
They furnish the necessary
power application between the
low energy levels of
controllers and the high
energy level needed to
perform their function in
control of the process.
Final Control Element
Final Control Element
Control Valve
A power operated device that manipulates
the fluid flow rate, temperature, level in a
process control system.
 It consists of a valve connected to an
actuator mechanism that is capable of
changing the position of a flow-controlling
element within the valve in response to a
signal from the controlling system.

Control Valves
Functions as a variable resistance, creating a
variable pressure drop in a pipeline
 This pressure-drop process is often called
throttling
 It is consists of three major sub-assemblies:

The valve body assembly

The internal trim parts
An actuator assembly
Variety of additional valve accessories
Control Valve
Actuator
Assembly
Valve
Positioner
Valve Body
Assembly
Actuator
The power to drive the valve.
 Power source could be:

Manual.

lever or gear box.
Pneumatic.
Hydraulic.
Electrical driven.
Valve Positioner
Control element determine the opening or
closing position, action and characteristic of
the valve.
 It receive signal from controller.
 It converts the signal to the appropriate
opening or closing setting of the valve.
 It provides the accurate control of the valve.

Valve Body
The part of a valve that is the main pressure
boundary,
 providing pipe connecting ends,
 the fluid flow passage way,

in some cases, the part that supports the seating
surfaces and closure member.
Control Valve
Size varies
from 1” to 36”
valve body!
Control Valves
Components Although there are so
many types and makes of
control valves, this drawing
can be used to illustrate the
location and description of
the different components
of control valve. The main
difference mainly will be
the type of actuator used
by different manufacturers.
Body Construction

In order to fulfill the
control valve function,
the valve body must:
Withstand the maximum
operating pressure.
Have adequate capacity in
respect of flow area.
Have correct flow
characteristic.
Be able to resist erosion
and corrosion.
Valve Body
All wetted parts of the control valve,
including external bolts/studs and nuts must
be designed to the same rating or equivalent
piping class.
 On the PEFS’s you will find the following
information:

DN 100 . P13001 . 3 309
Line Size in metric units
Pipeline Number
Rating of the Piping Equipment
Material Composition of Piping Equipment
Piping Class


The piping classes are divided in different sections
and the International Standard ANSI B.16.34 are
applicable with the exception of the Classes 125,
250 and 400
The following Classes are used and their
abbreviations:
1 = Class 150
3 = Class 300
6 = Class 600
9 = Class 900
15 = Class 1500
25 = Class 2500
Body Size
The control valve body size may have the
same size as the calculated trim size, but
oversized bodies, up to the size of the
adjacent piping, may be required to reduce
the outlet velocity of the fluid
 The control valve body size shall be
selected from the following series:

Metric Sizes: DN 25, 40, 50, 80, 100, 150, 200,
300, 400, 450, 500, 600, and larger
Imperial Sizes: 1”, 1-1/2”, 2”, 3”, 4”, 6”, 8”,
10”, 12”, 16”, 20”, and larger
Valve Trim
Reduced trim means bore
size smaller than port size
Full trim means bore size = port size.
End Connections


The following are the
possible connections for
control valves. Normally,
all control valves should
have flanged ends.
Some types of control
valves, such as Camflex
Valves and Butterfly
Valves do have flangeless
valve bodies, which are
less expensive.
Integral
Flange
Separable
Flange
End Connections
Socket-weld
Butt-weld
Threaded connections are not permitted for
Screwed process fluids. Allowed only for instrument air
regulators if flange type cannot be obtained
Globe Valves
 is
the most widely used control valve in
process control
 provides tight shut off
 withstand high differential pressure
 changeable flow characteristic
 by using different plug style offers a wide
range of sizes, pressure ratings, and flow
characteristics
Globe Valves

Single Seated Globe Valves:
This is the most preferred type for all
applications with the exception of very high
flow rates in combination with low pressure
drops
Globe Valves
Double Seated Globe Valves - provides
large capacities and ideal for high pressure
applications with dirty fluids
 Disadvantages

high leakage rate
very expensive
Globe Valves

Angle-Body Globe
Valve This type of valve is
designed specifically for
erosive liquid and gas
applications. Normally
installed with the flow
entering at the side and
leaving at the bottom
Globe Valves

3-Way Globe
Valves:
For combining or
diverting flow
applications;
provide large flow
with low-pressure
recoveries.
Flow Characteristics



Control valve Flow characteristics is the
relationship between flow rate through the valve
and valve travel as the travel is varied from 0 to
100%
CV: The VALVE FLOW COEFFICIENT is the
number of U.S. gallons per minute of 60 degree F
water that will flow through a valve at a specified
opening with a pressure drop of 1 psi across the
valve.
Inherent flow characteristic: refers to the
characteristic observed with at constant pressure
drop across the valve
Flow Characteristics

The three most common types of flow
characteristics are:
Equal percentage - The inherent flow
characteristic, which, for equal increments of
rated travel, will ideally give equal percentage
changes of the existing flow Cv at constant
Delta P.
Linear - equal increments of travel provide
equal increments of flow Cv at constant
pressure drop.
Flow Characteristics

Cont….
Quick opening – Provides for maximum change
in flow rate at low valve travels with a nearly
linear relationship. Additional increases in
valve travel give sharply reduced changes in
flow rate. Quick open plugs are used for on-off
applications designed to produce maximum
flow quickly.
Flow characteristics of globe valves can be deter-mined by the shape of the plug head.
Cavitation
A two-stage phenomenon of liquid flow
 The first stage is the formation of cavities
(vapor bubbles) within the liquid stream
 The second stage is the collapse or
implosion of those cavities (beyond the
vena contracta) back into an all liquid state
 The energy released by cavitating liquids
can, under certain circumstances, cause
physical damage of valve or piping
components

Pressure P1
P2
Liquid Vapor pressure
Pv
Velocity
PVc
Velocity
Pressure
Cavitation
Anti-Cavitation Valves -
For liquid services in which high pressure
drops occur, the application of a conventional trim with standard flow
direction often results in very high velocities and cavitation. This type of
application requires anti-cavitation valve.
Low Noise Valves - Liquid flow
noise, cavitation noise, and flashing
noise can be generated by the flow
of a liquid through a valve and a
piping system. Special design of
control valve is necessary to reduced
the noise level to acceptable value.
Pressure P1
Velocity
Pressure
Flashing
PVc
Liquid Vapor pressure
Pv
Velocity
P2
•The liquid pressure drops below the vapor pressure and remains
as vapor until the downstream pressure recovers.
•Flashing will cause choke flow condition to occur.
•In addition the vapor bubbles can also cause mechanical
damage to the valve and piping system.
Cavitation & Flashing
Recovery Point
Cavitation point
Packing Box and Bellows Seal -
The packing box or stuffing
box is the most commonly used stem seal. The bellows seal is used only
for highly toxic process fluid where leakage is not permissible. For
services with fluid temperature outside the packing material temperature
limits, an extended bonnet is used. Also for very low temperature service,
an extended bonnet is selected to prevent ice formation on the stem.
PTFE Internal Lining
Extended Bonnet
Standard Bonnet
Bellows seal
is used for corrosive or
highly toxic fluids.
Packing box
contains a number of
compressed packing
to maintain seal.
Miniature Valves -
are used for very small flows
size DN 25 (1”) and smaller.
VariPak Control Valve
made by Masoneilan
Advantages: Adjustable Cv
Can be adjusted from 100%
to 40 % without any change
of input signal and/or
control valve components
Large Cv range is achieved by changing
different plugs and different shape of seat.
Eccentric Rotary Plug Valve
(Camflex)
Can be substituted for globe-body
control valve.
 The seat portion of the plug has the
Camflex Valve
form of a spherical segment which is
rotated through 50 degrees for
maximum opening.
 The design eliminates high torque and
rapid wear of seat ring.
 The tight shut off is achieved through
the flexing action of the plug legs.

Rotary Globe Valve (Varimax)

Provide control of high pressure compressible fluids
without the erosion, vibration and high noise levels
associated with conventionally designed rotary
valves. Because of their relatively large flow
passages they are particularly well suited for
applications involving gases.
Varimax Valve
Butterfly Valve
High flow rate
 Low pressure drop
 Consists of a cylindrical body with a disk or
vane.
 Advantage - reduces the likelihood of
clogging.
 Disadvantages

Not tight shut-off
Flow characteristic cannot be change
Ball Valve
Similar to a butterfly valve except that its flowcontrol element is a sphere instead of a disk, and
thus has a greater seating area.
 Because of this, ball valves allow higher
differential pressures and better sealing.
 Normally used for on-off service (like emergency
shutdown application).
 The ball valve is not ideal for throttling service.

Actuators
Diaphragm
Spring-Opposed
Diaphragm Actuator
Spring Diaphragm Actuator
Spring
Set of Springs
Fail Open
Fail Close
Diaphragm
Fail Close
Fail Open
Multi-Spring, Spring
Diaphragm Actuator
Spring-Opposed Piston
Actuator
Long-Stroke
Piston
Actuator
Positioner Schematic for spring-diaphragm actuator or springopposed piston actuator.
Positioner Schematic - Two Output Signal
Control Valve Accessories
Filter Regulators - For control valves which
cannot handle the maximum air supply
pressure of up to 8 Bar, they are provided
with Air Filter Regulator.
 Filters - For actuators which can handle the
maximum air pressure, a Air Filters is used
instead of Air Filter Regulator.

Control Valve Accessories
Handwheels - For control valves which
needs to be open manually, in most cases
during plant start-up, require hand wheel.
The hand wheel facility is designed such
that one man can operate the valve.
 Limit Stops are provided to prevent the
control valve from fully closing or fully
opening.

Control Valve Accessories
Limit Switches are installed in control
valves to electrically indicate open, closed,
or intermediate position of the valve stroke
 Limit switches can either be

micro-switches enclosed in an explosion proof
box
or proximity sensors
Volume Boosters are used on throttling
control valves to provide fast stroking action
with large input signal changes. Depending on
the actuator size, packing set and the number
used, boosters can decrease valve stroking times
by as much as 90%.
Quick-Exhaust
Valves are applied
to achieve a specified
opening or closing
time
Lock-up Valves
are used for control calves which
must stay-put (remains at last
position) in case of an
instrument air failure. They are
known also as Stay-Put Valves.
Solenoid Valves are used to interrupt or cut-off air signal to
the actuator. It is used to switch a particular control valve or ESD
shut-off valve to their fail safe position (Fail Close or Fail Open).
Schematic of Control Valve Basic Piping
4 - 20 mA
From DCS
I
P
Pneumatic
Positioner
Valve
Actuator
Output To
Actuator
Current to
Pneumatic
Transducer
Pneumatic Signal
3 - 15 PsiG
Regulated
Air Supply
Setting dependent on
Actuator operating
pressure
Valve travel
Feedback to
Positioner
Instrument Gauges
Schematic of Double Acting Control Valve Piping
4 - 20 mA
From DCS
I
P
Valve
Actuator
Pneumatic
Positioner
Output
To Actuator
Valve travel
Feedback
to Positioner
Current to
Pneumatic
Transducer
Pneumatic Signal
3 - 15 PsiG
Regulated
Air Supply
Setting dependent on
Actuator operating pressure
Instrument Gauges
Example of ControlValve Piping
Schematic Drawing
Lock up
Valve
Set 3.4 Barg
Exh
A
B C
Exh
Trip Valve
Set 2.8 Barg
Signal
4-20mA
D
E F
POSITIONER
Air supply
Check
Valve
Booster Relay
Air Regulator
Set 3.8 Barg
Volume Tank
The valve remains at last position incase of Air Failure.
Instrument Standard
ANSI – American National Standards
Institute
 API – American Petroleum Institute
 ASME – American Society of Mechanical
Engineers
 ASTM - American Society for Testing and
Materials
 BSI – British Standard Institute

Instrument Standard





DIN – The German Institute for Standardization
ISO – International Organization for
Standardization
NEMA – National Electrical Manufacturers
Association
NIST – National Institute of Standards and
Technology
CENELEC - European Committee for
Electrotechnical Standardization
Thank You
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