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Main Target
 Definition
 Function
 Main parts
 Classifications
 Actuator
 Selection
 Problems
Definition
A valve is mechanical device that controls the flow of
fluid and pressure within a system
Function
1-stopping and starting fluid flow
2-varying the amount of fluid flow
3-controlling the direction of fluid flow
4-regulating down stream system or process
pressure
5-relieving component or piping over pressure
Main parts
1-body
2-bonnet
3-disk
4-seat
5-stem
6-actuator
7-packing
Introduction to the Type of
valves
Each type of valve has been designed to meet specific
needs. Some valves are capable of throttling flow;
other type can only stop flow. Other work well in
corrosive system and other handle high pressure fluid.
Each type has certain inherent advantages and
disadvantages.
Classification of valves
Valves may be classified in a number of ways
according to control
1-pressure control valve as relief valve
2-direction control valve as check valve
3-flow control valve as throttling valve
according to construction
1-gate valve
3-plug valve
5-pinch valve
7-globe valve
2-ball valve
4-reducing valve
6-diaphram valve
8-miscellaneouc valves
Common type of
valves
1- Manual valve
2- Check valve
3- Relief valve
Valve actuator
1-Mannual actuator
2-Electric actuator
3-Hydraulic actuator
4-Pneumatic actuator
Valve Selection
1- According to the type of fluid to be controlled and its
condition
2- According to the required condition required
Common Valve Problem
1-cavitation
2-high velocity
3-water hammer
Manual valves
:
A manual
valve:
is considered to be a valve that is operated
by plant personnel directly, by the use of
either a hand wheel/wrench or an on/off
actuator in the case of shutdown valves.
Function of Manual valves
Manual valves:
serve three major functions in fluid-handling systems:
1_Stopping and starting flow
2_controlling flow rate,
3_ diverting flow.
Manual valves type
Manual valves involve these types:
1_ Gate valves
2_Globe valves
3_ Plug valves
4_Piston valves
5_ Ball valves
6_ Diaphragm valve
7_ Butterfly valves
1_gate valve
1_ A gate valve is a linear motion valve
2_ used to start or stop fluid flow however,
it does not regulate or throttle flow.
3_ The name gate is derived from
the appearance of the disk in
the flow stream
Design and application of the gate valve
. Gate valves are primarily designed to serve
as isolation valves
. In service, these valves generally are
either
fully open or fully closed
. When fully open, the fluid flows through
the valve in a straight line with very
little resistance
. Gate valves should not be used in the regulation or
throttling of flow because accurate control is not
possible and disk will damage
. Designed for full-area flow to minimize the pressure
drop and allow the passage of a pipe-cleaning pig.
Construction of a Gate Valve
1-The body:
is generally connected to the
piping by means of flanged, screwed, or
welded connections..
2-The bonnet:
containing the moving parts, is joined
to the body, generally with bolts, to
permit cleaning and maintenance
3-The valve trim :
consists of the stem, the gate, the wedge,
or disc, and the seat rings.
TYPES OF GATE VALVE
1-Solid Wedge gate valve
. The solid wedge gate valve is the most commonly
used disk because of its simplicity and strength.
. A valve with this type of wedge may be installed in
any position and it is suitable for almost all fluids.
It is practical for turbulent
Solid Wedge gate valve
2-Flexible Wedge gate valve
. The flexible wedge gate valve is a one piece disk with a
cut around the perimeter to improve the ability to
match error or change in the angle between the
seats..
. Gate valves used in steam systems have flexible wedges
The reason for using a flexible gate is to prevent binding
of the gate within the valve when the valve is in the
closed position.
Flexible Wedge gate valve
3-Split wedge gate valves
. Split wedge gate valves: are of the ball and socket
Design
. This type of wedge is suitable for handling no
condensing gases and liquids at normal temperatures,
particularly corrosive liquids.
Split valves wedge gate
SOLID
WEDGE
SPLIT
WEDGE
FLEXIBLE
WEDGE
Other classification of gate valve
1_The parallel-gate valve
Use a flat disk gate as the closure element that
fits between two parallel seats
2_The knife-gate valve
. Has a sharp edge on bottom of the gate to
prevent entrained of solids
as well as to separate
slurries
3_The through-conduit gate valve
. Has a rectangular closure element with
a circular opening equal to the full-area
flow passage
Advantages of Gate Valves :
1_It can be applied to both liquid and gas services
2_They have good shut off characteristics
3_ The pressure loss through the valve is minimal
4_ the gate valve is relatively inexpensive
Disadvantage of gate valve
1_Gate valves are not quick opening or closing
valves.
2_Gate valves require large space envelope for
installation operation, and maintenance
3_High-flow velocity in partially opened valves
may cause erosion of the discs and seating
surfaces.
Ball valves
. Ball valve is a valve with a spherical disk
. Is a quarter-turn valve suitable for clean gas, compressed
air, and liquid service. They also can be used for slurry
service.
. The body of ball valves may be made of metal, plastic or
metal with a ceramic center.
. Ball valves can be used for service temperatures ranging
from ( 270 to 360 ᴼC)
HANDLE
Ball
valves
BALL
FLOW PASSAGE
Construction of a Ball Valve
Major components of the ball valve are:
1- Body
2-Spherical plug
3-Seat
Ball valves are made in three general patterns:
1-venturi port
2- full port
3-reduced port
Construction of a Ball Valve
Ball valve may be:
1- unidirectional
2- bidirectional
3- multidirectional
Depending on:
1- the number of valve ports
2- the number of valve seats.
Construction of a Ball Valve
Ball valves are referred to as :
2-way
3-way
4-way
5-way multiport valves.
Advantages of Ball Valves
1. Provides bubble-tight services
2. Quick to open and close.
3. Smaller in size than a gate valve.
4. Lighter in weight than a gate valve.
5. Multiport design offers versatility not available
with gate or globe valves.
6. Several designs of ball valves offer flexibility of
selection
7. Can be used in clean and slurry applications.
8. High-quality ball valves provide reliable service in
high-pressure and high-temperature
applications.
9. Force required to actuate the valve is smaller than
that required for a gate or a globe valve.
Disadvantages of Ball Valves:
1. They are not suitable for sustained throttling
applications
2. In slurry or other applications, the suspended
particles can settle and become trapped in body
C- Plug valves
. Plug valves are called cocks, generally are used for the
same full-flow service as gate valves, . where quick
shutoff is required.
. They are used for steam, water, oil, gas, and chemical
liquid service.
. They are available for pressure service from vacuum to
10000 psi (69000 k Pa) and temperatures from 50
to 1500 F (46 to 816 C).
Construction of a Plug Valve
Advantages of Plug Valves
The following summarizes the advantages of plug
valves:
1. Simple design with few parts.
2. Quick to open or close.
3. Can be serviced in place.
4. Offers minimal resistance to flow.
5. Provides reliable leak tight service.
6. Multiple port design helps reduce number of valves
needed and permits change in flow direction.
Disadvantages of Plug Valves
The disadvantages include:
1. Requires greater force to actuate, due to high
friction.
2. Reduced port, due to tapered plug.
3. Typically, plug valves may cost more than ball
valves.
Typical Applications of Plug Valves
1. Air, gaseous, and vapor services
2. Natural gas piping systems
3. Coal slurries, mineral ores, mud, and sewage
applications
4. Oil piping systems
5. Vacuum to high-pressure applications
Diaphragm Valves
A diaphragm valve is a linear motion valve
that is used to start, regulate, and stop fluid
flow.
The name is derived from its flexible disk,
which mates with a seat located in the open
area at the top of the valve body to form
a seal.
Construction of a Diaphragm Valve
There are three cases for diaphragm valve
1-open
2-throttling
3- closed
STEM
BONNET
COMPRESSOR
DIAPHRAGM
FLOW
VALVE BODY
FULLY OPEN
THROTTLED
FULLY CLOSED
Advantages of Diaphragm
Valves
1. Can be used as on-off and throttling
service valves.
2 Offer good chemical resistance due to
variety of linings available..
3. Stem leakage is eliminated.
4. Provides bubble-tight service
Disadvantages of Diaphragm
Valves
1.The weir may prevent full drainage of
piping
2. Working temperatures. and pressures are
limited by the diaphragm material.
3.The diaphragm may also limit the
hydrostatic pressure.
4. Diaphragm valves are available in
limited sizes.
Typical Applications of Diaphragm Valves
1. Clean or dirty water and air service
applications .
2. Demineralized water systems .
3. Corrosive applications .
4. Vacuum service .
6. Food processing, pharmaceutical, and
brewing systems .
Globe valves
• A globe valve is a type of valve used for
regulating flow in a pipeline,
• consisting of a movable disk-type
element and a stationary ring seat in a
generally spherical body.
• globe valves may be used for isolation
and throttling services .
The essential principle of globe valve operation
• is the perpendicular movement of the
disk away from the seat.
• This causes the annular space between the
disk and seat ring to gradually close as the
valve is closed.
• This characteristic gives the globe valve
good throttling ability, which permits its
use in regulating flow.
globe valve involve these types:
1. Tee Pattern globe valves
have the lowest coefficient of flow and
higher pressure drop
They are used in severe throttling services,
Tee pattern globe valves may also be used
in applications where pressure drop is
not a concern and throttling is required
2. Wye Pattern globe valves
offer the least resistance to flow
They can be cracked open for long periods
without severe erosion
They are extensively used for throttling
during seasonal or startup operations
They can be rod through to remove debris
when used in drain lines that are normally
closed. Refer to Fig
3.Angle Pattern globe valves
turns the flow direction by 90 degrees
without the Use of an elbow and one
extra weld
They have a slightly lower coefficient of
flow Than wye pattern globe valves
They are used in applications that have
periods of Pulsating flow
Advantages of a Globe Valve
1 .Good shutoff capability
2 .Moderate to good throttling capability
3 .Shorter stroke compared to a gate valve.
4 .Available in tee, wye, and angle
patterns, each offering unique capabilities.
5 .With disc not attached to the stem, valve
can be used as a stop-check valve
Disadvantages of a Globe Valve
1 .Higher pressure drop compared to
a gate valve.
2 .Requires greater force or a larger
actuator to seat the valve with
pressure under the seat.
3 .Throttling flow under the seat and
shutoff flow over the seat.
Applications of Globe Valves
1. Cooling water systems
2 .Fuel oil system
3 .High-point vents and low-point drains
when leak tightness
4 .Feed water, chemical feed, condenser
air extraction, and extraction drain
systems.
5 .Turbine seals and drains.
6 .Turbine lube oil system and others.
Butterfly valves
• called quarter turn valves
• Butterfly valves are used to control and
regulate or throttle the flow.
• They are characterized by fast operation and
low-pressure drop
They require only a quarter turn from closed
to full-open position.
 The "butterfly" is a metal disc mounted
on a rod. When the valve is closed, the
disc is turned so that it completely
blocks off the passageway.
 When the valve is open, the disc is
rotated a quarter turn so that it allows
unrestricted passage. The position of
the disc is effected from outside the
valve.
OPERATOR
BODY
SEAT
DISK
Advantages of Butterfly Valves
1. The compact design requires considerably
less space, compared to gate, globe, or other
valves.
2. Light in weight.
3. Quick acting; as a quarter-turn valve, it
requires less time to open or close.
4. They have low-pressure drop and high
pressure recovery.
5. It is available in large sizes
6. Provide bubble-tight service.
Disadvantages of a Butterfly
Valve
1.Throttling service is limited to low differential
pressure.
2.Cavitations and choked flow are two potential
concerns.
3.The disc movement is unguided and affected
by flow turbulence
Applications of Butterfly Valves
1. Cooling water, air, gases, and other similar
applications, such as fire protection,
circulating water, et cetera
2. Corrosive services requiring lined valves
3. High-pressure and high-temperature
steam services
4. Vacuum service
PISTON VALVES
In these valves,
the seat seal is achieved between the lateral
faces of the piston and the seat bore.
When the valve is being opened, flow cannot
start until the piston has been completely
withdrawn from the seat bore.
piston valves permit good flow control.
If sensitive flow adjustment is required,
the piston may be fitted with a needle
shaped extension.
Piston valves are also used for stopping
and starting flow when flow resistance
due to the tortuous flow passage is
accepted.
Like globe valves,
piston valves permit good flow control.
If sensitive flow adjustment is required,
the piston may be fitted with a needle
shaped extension.
Piston valves are also used for stopping and
starting flow when flow resistance due to the
tortuous flow passage is accepted.
NAME: Abdallah Omar El-sayed
CITY :Helwan
Governorate: Cairo
E-mail:[email protected]
Ph.No:01017828720
Is a mechanical device, a valve, which
normally allows fluid (liquid or gas) to
flow through it in only one direction.
Frank P. Cotter developed a "simple self
sealing check valve, adapted to be connected
in the pipe connections without requiring
special fittings and which may be readily
opened for inspection or repair" 1907.
Nikola Tesla invented a deceptively simple oneway valve for fluids in 1916 .
Construction of a Check
Valve
A basic check valve consists of a valve body, bonnet
or cover, and a disc which is attached to a hinge
and swings away from the valve seat to allow
fluid to flow in the forward direction, as in a
swing- or tilting-disc check valve, and returns to
valve seat when upstream flow is stopped. Thus,
reverse flow is prevented.
In folding disc check valves, the disc consists of two
halves attached in the middle.
The two halves fold backward when upstream
flow is initiated. Activated by a spring, the two
halves quickly close the flow path when
upstream flow ceases. In the case of lift-check
valves, the disc is in the form of a piston which
is moved out of the flow path by upstream
flow and returns to the valve seat by gravity to
stop back flow. Ball-check valves have a disc in
the form of a ball.
The Function of Check Valves
The prime function of a check valve is to protect
mechanical equipment in a piping system by
preventing reversal of flow by the fluid. This is
particularly important in the case of pumps
and compressors, where back flow could
damage the internals of the equipment and
cause an unnecessary shutdown of the system
and in severe cases the complete plant.
Check valves are automatic valves that open
with forward flow and close against reverse
flow. This mode of flow regulation is required
to prevent return flow, to maintain prime after
the pump has stopped, to enable
reciprocating pumps and compressors to
function
Check valve
The main parts of check valve
There are a number of reasons for
using check valves, which include:
1)Protection of any item of equipment that can
be affected by reverse flow, such as flow
meters, strainers and control valves.
2)To check the pressure surges associated with
hydraulic forces, for example, water hammer.
These hydraulic forces can cause a wave of
pressure to run up and down pipe work until
the energy is dissipated
3)Prevention of flooding.
4)Prevention of reverse flow on system
shutdown.
5)Prevention of flow under gravity.
6)Relief of vacuum conditions.
7)may also be required in lines feeding a
secondary system in which the pressure can
rise above that of the primary system.
Types of Check Valves
There are several types of check valves having
varying body configurations. The following are
some commonly used types of check valves:
1-Swing Check Valve
Is check valve in which the disc, the movable
part to block the flow, swings on a hinge or
trunnion, either onto the seat to block reverse
flow or off the seat to allow forward flow.
The seat opening cross-section may be
perpendicular to the centerline between the
two ports or at an angle. Although swing
check valves can come in various sizes, large
check valves are often swing check valves.
They are recommended for lines having low
velocity flow and should not be used on lines
with pulsating flow
Types of swing check valves
1-the flapper valve
2-the clapper valve
DISK NUT
ANGLE
PLUG
CAP
HINGE PIN
ARM
DISK
Swing check valve
Swing check valve
2-Lift check valves
Are particularly adapted for high-pressure
service where velocity of flow is high
Large steam jackets are located to eliminate
sticking because of differential expansion.
is commonly used in piping systems in which
globe valves are being used as a flow control
valve. They have similar seating arrangements
valves are suitable for installation in horizontal
or vertical lines with upward flow.
They are recommended for use with steam, air,
gas, water, and on vapor lines with high flow
velocities. These valves are available in three
body patterns: horizontal, angle, and vertical.
The disk or ball is forced onto the seat of the
valve by both the backflow and gravity.
The piston type lift check valves have a tendency
to stick in the open position when service fluid
has sediment trapped above the piston.
CAP
PLUG
DISK
OUTLET
INLET
SEAT
BODY
Lift check valve
3-Tilting Disc Check Valve
The tilting disk check valve is similar to the swing
check valve. Like the swing check, the tilting disk
type keeps fluid resistance and turbulence low
because of its straight-through design.
check valves can be installed in horizontal lines and
vertical lines having upward flow.
The tilting-disc check valve is designed to overcome
some of the weaknesses inherent in conventional
swing check valves .
•
A combination of design features enables the valve to
open fully and remain steady at lower flow velocities and to
close quickly upon cessation of forward flow.
•
It performs well in pulsating, turbulent, and highvelocity flows. These attributes prolong the valve’s lift and
reduce flow-induced dynamic loads on the piping system.
•
As flow decreases, the disk starts closing available with a
soft seal ring, metal seat seal, or a metal-to-metal seal. The
latter is recommended for high temperature operation. The
soft seal rings are replaceable, but the valve must be
removed from the line to make the replacement.
Tilting Disc Check Valve
Tilting Disc Check Valve
4-A ball check valve
A ball check valve is a check valve in which the
closing member, the movable part to block the
flow, is a spherical ball. In some (but not all)
ball check valves, the ball is spring-loaded to
help keep it shut. For those designs without a
spring, reverse flow is required to move the
ball toward the seat and create a seal.
They are commonly used in liquid or gel
High pressure (HP) pumps and similar applications
commonly use small inlet and outlet ball check valves
with both balls and seats made of artificial ruby, for
both hardness and chemical resistance.
After prolonged use, such check valves can eventually
wear out or the seat can develop a crack, requiring
replacement
Ball check valves should not be confused with ball valves,
which is a different type of valve in which a ball acts as
a controllable rotor to stop or direct flow.
An application in sucker rod pump in
Subsurface Pumping Unit
1)The standing valve
2)The travelling valve
A ball check valve
Start of upstroke
Start of down
stroke
Plunger falls through fluid
Fluid Lifted toward
surface
Tubing
Plunger
Traveling
valve
Barrel
Standing
valve
Seating nipple
Tubing
Plunger Moving Up
Plunger moving down
Traveling valve open
Barrel
Standing valve closed
Seating nipple
Ball & seat
Cage
5-Stop Check Valve
A stop check valve can either be used as a
unidirectional check valve or as an isolation
(stop) valve like a gate or globe valve.
These valves are available in tee-pattern, wyepattern, angle-pattern, and inclined pattern.
HANDWHEEL
BONNET
PLUG
SEAT
Stop Check Valve
6-Diaphragm Check Valves
The check valve consists of a perforated coneshaped
basket that supports a matching diaphragm.
Flow passing through the cone lifts the diaphragm off its
seat and lets the fluid pass. When forward flow ceases,
the diaphragm regains its original shape and closure is
fast.
One application worth mentioning is in purge-gas lines,
which feed into lines, handling slurry or gluey
substances. Under these conditions, diaphragm valves
tend to operate with great reliability, while other valves
hang up very quickly.
Because the diaphragm is elastically strained in the open
position, and travel of the lip from the fully open to the
closed position is short, the diaphragm check valve
closes extremely fast.
This valve is well-suited for applications in which the flow
varies within wide limits. However, the pressure
differential for which the valve may be used is limited
to 10 bar (145 lb/in2), and the operating temperature
is limited to about 74°C (158°F).
The inside of the sleeve is soft and capable of embedding
trapped solids.
Diaphragm check valve
Diaphragm check valve
SELECTION OF CHECK VALVES
1)closing speed
2) the closing characteristic of the valve
3) size
SELECTION OF CHECK VALVES
Most check valves are selected qualitatively by
comparing the required closing speed with the
closing characteristic of the valve.
This selection method leads to good results in
the majority of applications. However , sizing
is also a critical component of valve selection
If the application is critical, a reputable
manufacturer should be consulted.
Check Valves for incompressible Fluids
These are selected primarily for their ability to
close without introducing an unacceptably
high surge pressure due to the sudden shutoff of reverse flow.
Selecting these for a low pressure drop across
the valve is normally only a secondary
consideration
Check Valves for Compressible Fluids
Check valves for compressible fluids may be
selected on a basis similar to that described
for incompressible fluids. However, valve
flutter can be a problem for high lift check
valves in gas service, and the addition of a
dashpot may be required.
Where rapidly fluctuating gas flow is
encountered, compressor-type check valves a
good choice.
Application Considerations
1)The force of gravity .
2) The flow velocity of the fluid.
3) The valve should be sized .
4) a check valve should not be located
immediately downstream of a source of
turbulence.
5) the fluid pressure
The force of gravity plays an important role in the
functioning of a check valve and, therefore, the
location and orientation of the check valve must always
be given consideration. Lift and ball check valves must
always be placed so that the direction of lift is vertical.
Swing checks must be located to ensure that the disc
will always be closed freely and positively by gravity.
The flow velocity of the fluid through the valve has a
significant effect on the life of the check valve. The
valve should be sized such that the fluid velocity under
normal conditions is sufficient to keep the disc fully
open and pressed against the stop. This minimizes disc
fluttering, which is the primary cause of valve failure.
A swing check valve may be used in the vertical run of a
pipe only when flow is upward.
the fluid pressure must be adequate to overcome the disc
weight and swing it to the fully open position.
When the flow is suspected to be pulsating and low, use
of a swing check valve is not recommended. Due to the
continuous flapping of the swing disc against the seat,
valves suffer considerable damage, and at times the
swing discs can come loose.
The user must evaluate specific application features to
determine the right valve for the application.
Advantages of Check Valves
They are self-actuated and require no external
means to actuate the valve either to open or
close. They are fast acting.
Generally speaking check valves have no
requirement for operators, and so the valve is
operated automatically by flow reversal;
however, in very special circumstances this
unidirectional facility has to be overridden.
Disadvantages of Check Valves
The following are some of the disadvantages
that are attributed to check valves:
1) Since all moving parts are enclosed, it is
difficult to determine whether the valve is
open or closed. Furthermore, the condition of
internal parts cannot be assessed.
2)Each type of check valve has limitations on its
installation configurations.
3)Valve disc can stick in open position
PRESSURE RELIEF VALVES
• Pressure relief device:
• A device designed to open in response to excessive
internal normal or subnormal fluid pressure, and
sized to prevent the fluid pressure from exceeding a
specified normal or subnormal limit.
• The device may be either of the type that closes
after the pressure excursion has receded or of the
non-reclosing type.
• Pressure relief valve:
• A pressure relief device that recloses automatically
after the pressure excursion has receded.
TYPES OF PRESSURE RELIEF VALVES
1.Direct-loaded pressure relief valve
2.Pilot-operated pressure relief valve
1.Direct-loaded pressure relief
valve
A pressure relief valve in which the fluid
pressure acting on the disc in the opening
direction is opposed by a direct mechanicalloading device such as a weight or a spring.
2.Pilot-operated pressure relief
valve
A pressure relief valve consisting of a main valve
that is the actual pressure relieving device,
and a self actuated pilot that controls the
opening and closing of the main valve by
either pressurizing or depressurizing the
dome of the main valve.
Pilot-operated pressure relief valve with direct-acting pilot
Type of Direct-loaded pressure relief
valve
A . Safety valve: A direct-loaded pressure relief valve
that is intended mainly for gas, vapor, or boiler and
steam applications and characterized by
pop-opening action.
B. Safety relief valve:
A direct-loaded pressure relief valve that may be
used either in gas or vapor service or in liquid
service. The valve will open in gas or vapor
service with a pop action, and in liquid service
in proportion to the rise in overpressure
though not necessarily linearly.
Type of Safety relief valve
1 .Conventional safety relief valve:
A pressure relief valve in which the loading device is enclosed
in a pressure-tight bonnet that is vented to the valve outlet.
2.Balanced safety relief valve:
A pressure relief valve that incorporates a means
for minimizing the effect of back pressure on the
performance characteristic.
Bellows BBalanced Safely Relief Valve,
Bonnet Vented. (Courtesy of Sempell A.G.)
Bellows
Relief Valve
3.Supplementary loaded pressure relief valve:
• A direct-loaded pressure relief valve with an
externally powered auxiliary loading device that
is designed to inhibit valve simmer by introducing
a supplementary seating load during normal
operation of the pressure system.
• Depending on the Code of Practice, the
supplementary-loading force augmenting the
spring force may be restricted or unrestricted.
The load is automatically removed at a pressure
not greater than the set pressure of the valve.
4.Assisted pressure relief valve:
• A direct-loaded pressure relief valve with an
externally powered auxiliary assist device that is
designed to inhibit valve chatter by introducing a
supplementary lifting force when the valve is
called upon to open.
• When the safe operating pressure is restored,
the assist device is deactivated and the valve
closes normally.
• If the power to the assist device should fail, there
is no interference with the normal operation of
the valve.
Assisted pressure relief valve
5.Liquid Relief Valves :
Normally, liquid relief valves differ
from conventional safety relief valves
only in a slight modification of the
geometry around the disc to achieve a
specific performance in liquid service.
Safety Relief Valve with Open Bonnet. [Courtesy of Crosby Valve & Gage Company,
Wrentham, MA.)
6.Vacuum Relief Valves
2.Type of Pilot-operated pressure relief
valve
1.Pilot-operated pressure relief valve with direct-acting
pilot:
A pilot-operated pressure relief valve in which the pilot
represents a pressure actuated three ported valve that
controls the operation of the main valve.
2.Pilot-operated pressure relief valve
with indirect-acting pilot:
A pilot-operated pressure relief valve in which
the pilot represents a spring loaded pressure
relief valve that controls the operation of the
main valve by the fluid being discharged
System Characteristics
1.Operating pressure:
The maximum pressure that is expected during normal
operating conditions.
2.Operating pressure differential:
The pressure differential between operating pressure and set
pressure expressed as a percentage of the set pressure or
in pressure units.
3.Maximum allowable working pressure:
The maximum pressure at which the pressure system is
permitted to operate under service conditions in
compliance with the applicable construction code for the
pressure system. This pressure is also the maximum
pressure setting of the pressure-relief devices that protect
the pressure system.
4.Accumulation:
The pressure increase in the pressure system over the
maximum allowable working pressure, expressed in
pressure units or percent of the maximum allowable
working pressure.
5.Maximum allowable accumulation:
The maximum allowable pressure increase in the fluid
pressure over the maximum allowable working pressure
as established by applicable codes for operating and fire
contingencies, expressed in pressure units or percent of
the maximum allowable working pressure.
6.Overpressure:
The pressure increase over the set pressure of the relieving
device, expressed as a percentage of the set pressure or
in pressure units.
Introduction
Some type of actuator is necessary to allow for the
positioning of a valve. Actuators vary from simple
manual hand wheels to relatively complex electrical and
hydraulic manipulators
Choosing the type of actuator
Valve actuators are selected based upon a number of
factors including torque necessary to operate the valve
and the need for automatic actuation.
Types of Actuators
The following are some of the commonly used
valve actuators:
•Mechanical Actuators
•Pneumatic Actuators
•Hydraulic Actuators
•Electric Motors
Mechanical Actuators
Is Manual, Fixed, and
Hammer Actuators
Manual actuators are
capable of Fixed
Handwheel placing the
valve in any position but
do not permit automatic
operation.
the hammer handwheel
moves freely through
a portion of its turn and
then hits against a lug on
a secondary wheel. The
secondary wheel is
attached to the valve
stem. With this
arrangement, the valve
can be pounded shut for
tight closure or pounded
open if it is stuck shut.
Manual Gear Head
If additional
mechanical advantage
is necessary for
a manually-operated
valve, the valve
bonnet is fitted with
Manually-operated
gear heads as
illustrated in Figure
Pneumatic actuators
Pneumatic actuators utilize the motive force provided by
a compressed gas such as air, nitrogen , or other
inert gas.
Pneumatic actuators are the most common type
of actuator because of
1-cheap and readily available power source less
expensive ,which is compressed air
2- less complex in design and so are easier to maintain.
3- Pneumatic actuators can be used on valves of
most sizes.
Types of Pneumatic Actuators
There are three basic types of pneumatic
actuators, given below
1- Diaphragm air actuator.
2- Piston type air actuator.
3- Vane type actuator.
Electric actuators
An electric motor provides the actuating energy to
place the valve in the desired position. Modern
electric motor powered actuators allow local,
remote, and hand operation and they are available
for a variety of types of valves and sizes.
Hydraulic Actuators
Hydraulic actuators are capable of
delivering very high torques, and with
it the fast stroking speed necessary to
operate larger valves
Hydraulic actuators utilize pressurized
liquids, usually oils but sometimes
water, or the process liquid is used to
provide the motive force for actuating
the valve.
Actuator specification sheet
To ensure that the actuator meets all the
process requirements and to avoid any
confusion, it is essential that an Engineering
Specification Sheet be created for each valve
that will be operated by an actuator. This sheet
must contain technical information about the
actuator and the valve body that it will be
attached to. This will avoid any confusion within
the design group and it will also allow
procurement to confidently place requisitions
with potential suppliers.
Sizing actuators for control valves
When an actuator for a control valve is sized it is
essential that the worst possible case is considered
when the valve is open/closed or in the throttling
mode.
Spare parts and maintaining
Actuated valves
When actuators are selected it is usually for the
duration of the plant life, which is usually 20 to 25
years. It is therefore necessary to consider ordering
spare parts when the actuator is purchased.
1. Type of fluid to be controlled
2. Temperature of fluid
3. Viscosity of fluid
4. Specific gravity of fluid
5. Flow capacity required
6. Inlet pressure at valve
7. Outlet pressure
8. Pressure drop during normal flowing
9.Maximum permissible noise
10.Degrees of existence of flashing
11.Inlet and outlet pipeline size