INSTRUCTOR:
ROBERT A. MCLAUGHLIN
ZAILI THEO ZHAO
1
AUTOMATED CONTROL VALVES &
PRESSURE REGULATORS
WEEK - 6
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POWER
EQUIPMENT
LEARNING OBJECTIVES
Understanding of the fundamentals of
automation, classification, and terms associated
with automatic valves.
 Identify the types of actuators and control valves
used in automation systems.
 Determine the three categories of control valves.
 Define the functions of the control valve actuator,
application and limitations, troubleshooting and
repair of actuators.
 Identify the types of pressure reducing valve and
operating principles associated with each type.
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
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AUTOMATED VALVES
automate?
 Advantages:
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 Why
Increases process efficiencies
 Reduced manpower/maintenance
 Increase safety
 Quicker more reliable control
 Increase mechanical advantage


Disadvantages
Greater initial cost
 Complexity, more personal training
 Higher qualification of workers

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DEGREES OF AUTOMATION
Fully automated
control
 No direct human
intervention
needed
 Semi-automated
control
 Periodically
requires human
intervention

Part automated – Part
manual
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
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AUTOMATION CLASSIFICATION
THREE BROAD CATEGORIES
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
Position control


Speed control


An elevator
Rotating equipment like turbines, diesels etc.
Process control

Regulating of temperatures, pressures, fluid flow,
tank levels, density control
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AUTOMATION CLASSIFICATION
SIMPLE ‘DISPENSING’ SYSTEM
Process control valves include the
three categories:

Dispensing


Seem like flow control
Dissipating


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
Seem like pressure control
Distributing

Seem like direction control
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AUTOMATION CLASSIFICATION
SIMPLE ‘DISPENSING’ SYSTEM
Process control valves - three
categories:
 Dispensing
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
The control valve dispenses steam or
water for functions like temperature
control.
 A lube oil cooler will have a valve
control valve to regulate the flow of
the cooling fluid through the cooler
to maintain a constant temperature


A superheater attemperator control
valve dispenses saturated steam to
the superheated steam to control
the final temperature
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CLASSIFICATION
SIMPLE ‘DISSIPATING’
SYSTEM
Dissipating
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
Pressure dissipation
 Pressure regulation falls into this category


The automated valve regulates system pressure, high
pressure inlet and a controlled lower pressure outlet
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AUTOMATION CLASSIFICATION
SIMPLE ‘DISTRIBUTING’ VALVE
Distributing

Dividing a process flow into separate lines or tanks
The main slide valve has two coupled shells.
 The inner shell is the actual distributing valve.
 In the fully left position, it connects the left cylinder end with the
channel B and the right cylinder end with the channel A.
 When the main slide valve moves to the right by the action of the
eccentric, it closes both ports.
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

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TERMS AND DEFINITIONS ASSOCIATED
WITH AUTOMATED VALVES
Valve capacity


Rate of flow through a valve
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
Dead Band
The amount of diaphragm pressure change that will
not bring about valve stem movement.
 A good way to think of dead band in mechanical
systems is to consider the lost motion in a connecting
linkage due to excessive bushing or pin wear.
 Excessive friction can also cause dead band to occur.

This is also known as lost motion.
 In some control systems, we do not want small variations in
the feedback signal to move the stem.
 Most automated valves will allow the operator to set the
sensitivity of the valve, in other words set the dead band.

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TERMS AND DEFINITIONS ASSOCIATED
WITH AUTOMATED VALVES
Feedback signal
I ’s the measured signal that determines what the valve
has to do.
 In a system in which pressure is being regulated, as the
controlled pressure is rising, the feedback tells the valve to
move in the closed direction.


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
Diaphragm Pressure Span
The low and high actuating signals that the diaphragm
valve operates.
 For example,




a diaphragm pressure control valve may be controlling system
pressure to 25 psi.
To regulate this signal, the diaphragm will receive a pneumatic
air signal from the air pilot controller from 5 psi to 25 psi.
From this situation, the diaphragm pressure span is 20 psi.
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TERMS AND DEFINITIONS ASSOCIATED
WITH AUTOMATED VALVES
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
Direct or Indirect
Acting
Refers to is the control air signal to the valve is to the
top or bottom of the diaphragm.
 In direct acting valves the signal is on the top of the
diaphragm and increasing air pressure causes the
diaphragm and actuator stem to move downward.
 In indirect or reverse acting actuators, the signal is
to the bottom of the diaphragm and increasing air
pressure causes upward movement of the actuator
stem.

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TERMS AND DEFINITIONS ASSOCIATED
WITH AUTOMATED VALVES
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
Fail Open


Fail Closed


The valve opens wide if an air pressure failure occurs
The valve closes if air pressure failure occurs
Fail Safe

The valve remains the in a fixed position when air
pressure failure occurs
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TERMS AND DEFINITIONS ASSOCIATED
WITH AUTOMATED VALVES
Closed Loop System
The valve process output is
measured and sends a
feedback signals to a controller.
 The controller compares this
signal to the set point signal,
and then tells the valve what to do (open more, …… ).
 This is a closed loop system.

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
Open loop system has no feed back signal
 Transducer


A device that changes a pressure or temperature
signal into an electrical signal.
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VALVE ACTUATORS TYPES
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A valve actuator is what
causes the position of the
seat to actually move.
 Some common actuators are:

Diaphragm actuators
 Piston actuators
 Electric motor actuators
 Solenoid actuators
 Hydraulic actuators

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VALVE ACTUATORS TYPES
Diaphragm actuators – very common in
steam/condensate systems
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
By using large diaphragms, a very small air signal to
the diaphragm can have huge mechanical advantage
to move the valve disc.
 Direct acting – signal is on top of diaphragm
 Indirect acting – signal is to the bottom of
the diaphragm

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VALVE ACTUATORS TYPES
Piston (cylinder) actuators – uses a piston to
position the valve disc.
 Most common application is ball and butterfly
valves
 More expensive than diaphragm valves
 Greater internal friction
 Very small and quite
powerful for their size
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
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VALVE ACTUATORS TYPES
Electric motor actuators – they are usually used
when high speed valve movement is necessary or
long strokes are required in large valves.
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
Relatively low torque outputs.
 Very expensive

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VALVE ACTUATORS TYPES
Solenoid Actuators – used for on/off applications
only and are quite small.
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
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VALVE ACTUATORS TYPES
Hydraulic actuators – use hydraulic fluid to
position the valve.
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
Requires a complete hydraulic system
 Very expensive
 Very powerful for their small size.

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ACTUATOR PROBLEMS
Packing gland to tight
 Stem worn or damaged
 Corrosion inside the valve
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Leaking diaphragms – causes
 Poor reaction to signal change
 Excessive air consumption
 Control valve will not stay in position
 Note – a leaking air line from a pilot controller
to the valve diaphragm can cause the same
symptoms.
 Valve stem sticking – causes
 Poor valve reaction
 Stem sticking can be cause by


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PRESSURE REDUCING AND
REGULATING VALVES
Pressure reduction is achieved
by placing a restriction in the
line
 A simple pressure reduction
can be accomplished by
placing an orifice in a line.
If either the inlet pressure
varied or the demand changed
on the low pressure side, the
pressure would vary.
 To keep the regulated pressure
constant, you need to vary the
orifice size.
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

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PRESSURE REDUCING AND
REGULATING VALVES
There are two ways to
automate pressure reduction.
 Multi component
automated control loops
 Self contained pressure
regulating valves
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
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PRESSURE REDUCING AND
REGULATING VALVES
Multi component control
loops
 Minimum requirements
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
Pressure sensing device
 Pilot pressure controller
 Actuated valve


The control pilot controller
receives a signal from the
reduced pressure side of the
system and sends a operating
signal to the diaphragm control
valve.
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PRESSURE REDUCING AND
REGULATING VALVES
Multi component control loops
 Two types of valves are
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
An upward seating
single valve disc
 A downward seating
single valve disc.


Both of these valves are single
seated unbalanced valves


They are the least expensive valve seating
arrangement.
The valve can have a single seat
which is balanced

Balance seats are arranged so high pressure
acts on both sides of the seat which allows the
valve to be operated with less effort.
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PRESSURE REDUCING AND
REGULATING VALVES
Multi component control loops
 Valve can also have
two discs on one valve
stem, which are
also
balances.
 It is called a double
seat pressure balanced plugs.
 The high pressure medium enters between the
two seats and exerts opposing forces on each of
the seats
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
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PRESSURE REDUCING AND
REGULATING VALVES

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Self contained pressure
regulator has all of the
control components
needed in one valve.
 Automatically reduce
supply pressure to a
preselected pressure

As long as the supply
pressure is at least as
high as the selected
pressure.
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PRESSURE REDUCING AND
REGULATING VALVES
The principal parts:
An upward-seating main
valve that has a piston on
top of its valve stem,
 An upward-seating
auxiliary valve,
 A controlling diaphragm,
 An adjusting spring and
screw.


The pressure entering
the main valve assists
the main valve spring in
keeping the reducing
valve closed by pushing
upward on the main
valve disk.
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
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PRESSURE REDUCING AND
REGULATING VALVES


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Some of the high pressure is
bled to an auxiliary valve.
 The auxiliary valve controls
the admission of high
pressure to the piston.
 The piston has a larger
surface area than the
main valve disk,

Open the main valve.
The auxiliary valve
is controlled by a
diaphragm.
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PRESSURE REDUCING AND
REGULATING VALVES
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PRESSURE REDUCING AND
REGULATING VALVES
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The control system below
shows a supply service
arrangement.
 The variable pressure
sensing line is actually
measuring the pressure
exerted by the column of
water above the sensing
point of the variable pressure
line to the water level.
 As the water level changes,
the pressure will vary
in the variable line.

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THANK YOU
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