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Agenda
Introduction to valves
Types of Valves and their operation
Advantages, disadvantages,
selection and specifications for
valves
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Introduction
What is a Valve?
Valves are the most common components in process piping
systems.
They are the main method of fluid (liquid & gas) control for:• Flow
• Pressure
• Level
• Temperature
•Thus they are any device for closing or modifying the passage
through a system, inlet or outlet, in order to stop, allow, or control
the flow of a fluid media.
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Introduction
Valves may be required to operate continuously e.g.
Control valves.
They may be operated intermittently e.g. Isolation / Stop
valves.
They may be installed to operate rarely e.g. Safety
valves.
A valve can be a very simple, low cost item or it may be
a very complicated, expensive item.
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Valve Parts
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Valve parts- Body
The majority of the
valve consists of the
valve body, including
most of the exterior.
The valve body is the
vessel or casing that
holds the fluid going
through the inside of
the
valve.
Valve
bodies
are
most
commonly made of
various
metals
or
plastics.
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Valve parts- Bonnet
A bonnet basically acts as a
cover on the valve body. It is
commonly
semi-permanently
screwed into the valve body.
During manufacture of the
valve, the internal parts are put
into the body and then the
bonnet is attached to hold
everything together inside. To
access internal parts of a valve,
a user would take off the
bonnet,
usually
for
maintenance. Some valves do
not have bonnets; for example,
plug valves usually do not have
bonnets.
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Valve parts- Hand wheel
Many valves are controlled
manually
with
a
handle
attached to the valve stem, this
is called a hand wheel and is
pictured on this slide. The
centre of the wheel is threaded
and acts against the thread on
the upper section of the stem.
When the wheel is turned it will
open or close the valve.
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Valve parts- Stem
The stem is a rod or similar
piece spanning the inside and
the outside of the valve,
transmitting motion to control the
internal disc or rotor from outside
the valve. Inside the valve, the
rod is joined to the disc. Outside
the valve the stem is attached to
a handle or another controlling
device. Between inside and
outside, the stem typically goes
through a valve bonnet if there is
one. In some cases, the stem
and the disc can be combined in
one piece, or the stem and the
handle are combined in one
piece.
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Valve parts- Stuffing Box & Glands
A stuffing box (or packing gland)
is a type of seal placed around a
valve stem at the point it exits the
valve body. It is the most common
method for preventing liquid or
gas from escaping the valve while
still allowing the shaft to turn or
slide.
In a conventional stuffing box, the
seal itself is provided by packing
rings, or a square cross-sectioned
rope, made of greased Carbon or
PTFE (Polytetrafluoroethylene ),
which is packed or wound tightly
around the stem, and compressed
in place with a threaded nut and
spacer.
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Valve parts- Stuffing Box & Glands
The box may also be fitted
with an opening for periodic
insertion of grease between
the rings, and sometimes
with
a
small
grease
reservoir.
Graphite Packing Material
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Valve parts- Discs, Plugs & Gates
This is the closure member
of the valve. Discs, Plugs
and Gates are connected
to the stem which is slid or
screwed up or down to
throttle the flow. The
relevant closure member
will then be forced down
into the seat to form a seal
when the valve is in a
closed position
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Valve parts- Seat Rings
The seat ring is where the Gate, Disc
or Plug of the valve sits when closed
and provides a stable, uniform and
replaceable shut off surface. Seat rings
are usually held in place by pressure
from the fastening of the bonnet to the
top of the body. This pushes the cage
down on the lip of the seat ring and
holds it firmly to the body of the valve.
Seat rings may also be threaded and
screwed into a thread cut in the same
area of the body. However this method
makes removal of the seat ring during
maintenance difficult if not impossible.
Seat rings are also typically beveled at
the seating surface to allow for some
guiding during the final stages of
closing the valve.
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Quiz
1. The majority of the valve consists of the valve ____,
including most of the exterior.
2. What is this valve part?
3. What material is shown here?
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General Operating Procedures
When operating process valve, best industry practices should be
observed and these are highlighted below.
All valves should be kept in the best general condition possible, and
should be exercised (opened and closed) at least three times a year
when possible. Valve stems may be lubricated occasionally but care
should be taken not to contaminate the packing as this may degrade
the material being used. Any leaking packing should be dealt with
promptly as this condition will only deteriorate, if it does not stop
leaking after being tightened down on the packing retention nuts and
bar, then it should be reported to a supervisor and be repaired by a
maintenance technician.
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General Operating Procedures
Some valves may be tightened or opened with
the aid of a ‘wheel key’ but great care must be
taken not to overtighten a valve as this can
cause damage to the wheel, stem and seat of
the valve. ‘Soft seat’ valves which are often
used in gas service (commonly Hydrogen)
should never be operated with a wheel key as
this not necessary, if a seal cannot be made on
a soft seat valve when hand tight, there is a
very good chance that a foreign material is
stuck inside the valve body and tightening with
a wheel key will have no advantage, the valve
will need to be removed for maintenance.
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Wheel Key
Wheel Key in use
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General Operating Procedures
Leaking packing can be repaired in valves but this must be done by a
qualified technician, packing can be added to, as well as replaced but this
must be decided upon by the technician as an over packed seal can be
as hazardous as a leaking one. Great care must also be taken when
choosing the grade and type of packing as certain processes require
different qualities from the seal material.
All packing must be done when the valve is not in use and is depressured
but not necessarily removed.
Various types and grades
of Valve Packing
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Quiz
• What is this tool?
• What 4
variables can a valve control?
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Valve Types & Selection
•
The main types of valves used in the Petrochemical/ Refinery/ Oil
Industry are: Globe Valve, Butterfly Valve, Diaphragm Valve,
Gate Valve, Control Valve, plug valve, ball valve, safety valve,
needle valves, angle valves etc.
•
Valves are selected for their:•
•
•
•
•
•
•
Ability to throttle flow
Lack of turbulence or resistance to flow when fully open
Quick opening and closing mechanism
Tight shut off
Ability to allow flow in one direction only
Opening at a preset pressure for pressure control
Ability to handle abrasive substance without rapid wear
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1. Flow regulation/Throttle valves
•Many
applications require the flow of the fluid to be
regulated (throttled) at some fixed level between zero
and maximum flow limits.
• Valves used for this job include Globe valves, Needle
valves, Angle valves & Butterfly valves.
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2. Pressure regulation
• In many applications, especially with gases, there is a
need to reduce the supply pressure to a set fixed
value.
• It
may also be necessary to maintain this reduced
pressure over a range of fluid flow conditions.
• The Pressure regulator valve (which has a Globe valve
design) is used for this job.
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3. Non-Return or Check Valves
• In
some circumstances it is important to prevent
reversed fluid flow.
• The
type of valve used for this job is called a Nonreturn-valve (NRV) or Check valve.
• Three main valve types are used for this job:
LIFT CHECK VALVE
SWING CHECK VALVE
BALL CHECK VALVE
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4. Pressure Safety Valves
•
Pressure Safety Valves (PSV) are used in liquid & gas service
applications where too much pressure in the system can cause
damage or are a safety risk.
•
All closed vessels where pressure could build up are protected by a
Pressure Safety Valve.
•
An important part of the relief valve installation is the routing of the
relieved fluid.
Normally relieved Liquid is returned to a service tank or
unpressurised part of the system.
•
•
•
The gas released from a PSV normally goes to the Flare.
•
Valves used for safety applications and require regular inspections
to check the settings and the operation
Return
lines
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must
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open.
5. Isolation/Stop Valves
• Valves
used for this job include Gate valves, Globe
valves, Ball valves, Plug valves & Diaphragm valves.
• The
isolation of the downstream system from the
upstream system by use of an isolation or stop valve is
a very important function.
• The main requirements of these valves are: Tight shut off when closed.
 Minimum restriction to flow when open.
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5. Isolation/Stop Valves
• The
isolation of the downstream system from the
upstream system by use of an isolation or stop valve is
a very important function.
• The main requirements of these valves are: Tight shut off when closed.
 Minimum restriction to flow when open.
•Valves
used for this job include Gate valves, Globe
valves, Ball valves, Plug valves & Diaphragm valves.
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6. Valve Specifications & Selection
Specifications to consider when selecting valves are;-
• Diameter.
• Working pressure.
• Operating temperature.
• Type of fluid.
• Valve material i.e. brass,
• End
configuration i.e. threaded,
socket weld, butt weld, push on,
soldered ends, clamp, grooved,
flangeless, lugged, mechanical joint
or flanged.
• Valve actuation method, i.e. Electric,
Pneumatic, Hydraulic or Manual.
bronze, copper, cast iron,
ductile iron, stainless steel,
plastics.
• Seat features i.e. metal to metal, soft
seat, o-ring.
• Valve Class i.e. IV, V or VI ANSI • Applications
Standards, ASME Standards,
Country standards etc.
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i.e.: Refinery, Chemical,
Petrochemicals, laboratory waster
waste, fire service, etc.
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Quiz
1. Name 3 valves that can be used for throttling flow.
2. Name 3 valves that can prevent non return of a fluid
down a pipeline.
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Quiz
3. Which one of the following valves should not be used
as a stop/isolation valve?
1.
2.
3.
4.
5.
6.
Gate
Plug
Ball
Diaphragm
Globe
Needle
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Quiz
4. Name one valve that rarely operates when in normal
service?
Ans:
5. State 8 considerations when selecting a valve for
use?
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Types of Valves- Gate
•
Gate valves are probably the most widely used valve type in the
Petrochemical / Refining/Oil & Gas Industry.
•
•
Needed as stop valves to fully shut off or fully turn on flow.
They are used in services that require infrequent valve operation,
and where the disc is kept either fully opened or closed. They
are not practical for throttling. With the usual type of gate valve,
close regulation is impossible. Velocity of flow against a partly
opened disc may cause vibration and chattering, and result in
damage to the seating surfaces.
•
There are two main types of gate valve:
1. RISING STEM
2. NON-RISING STEM
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(RISING STEM)
• Gate valve
Types of Valves- Gate
Types of Valves- Gate
• Gate valve
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(RISING STEM)
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Types of Valves- Gate
• Gate valve
(RISING STEM)
• In the rising stem gate
valve the threaded
(screwed) part of the
stem is outside of the
valve.
• The position of the rising
stem shows if the valve
is open or closed.
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Types of Valves- Gate
• Gate valve (RISING STEM)
•
In this construction the stem screw
remains outside the valve body
whether the valve is opened or
closed. Stem threads are not
subjected to the effects of fluids in
the line such as corrosion, erosion,
sediment, etc. This construction also
permits convenient lubrication of
stem threads.
•
The rising stem shows at a glance the
position of the disc. Adequate
headroom must be provided for the
rising stem when the valve is opened
& the stem should be protected
against damage when raised.
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Types of Valves- Gate
• Gate valve
(Non RISING STEM)
In the non-rising stem gate valve
the threaded (screwed) part of the
stem is inside the valve.
Stem does not rise when disc is
raised, but merely turns with the
hand wheel. Ideal where head
room is limited. Since stem
merely turns when operated, wear
on packing is minimized.
It is difficult to see if the valve is
open or closed.
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Types of Valves- Gate
• Gate valve
(Non RISING STEM)
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Types of Valves- Gate
• Gate valve
(Non RISING STEM)
Gate Valve (NON-Rising Stem)
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Types of Valves- Gate
Advantages:
Laminar flow, low pressure drop when fully open
Offer reasonable flow-rate regulation
Cheap to manufacture
Very robust (strong) construction
They can be used both ways
Disadvantages:
Sediment or dirt may stop the gate closing fully
The base of the gate is liable to wear by erosion if
operated partly open
The gate valve is difficult to operate when opening
or closing against fluids at a very high pressure
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Types of Valves- Globe
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Types of Valves- Globe
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Types of Valves- Globe
Globe Valve
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Types of Valves- Globe
CLOSED
OPEN
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Types of Valves- Globe
Comparison
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Types of Valves- Globe
Advantages:
Good flow regulation
Positive shut-off
Can be used in high pressure systems where positive shutoff is essential for safe operation
Disadvantages:
x High pressure drop even when the valve is fully open
x Large amount of force required to operate at high pressures
x The valve seats can be damaged and jammed by solids
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Types of Valves- Ball
In ball valve the flow control element, is in the shape of a ball with an opening or
port which allows liquids to pass through.
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Types of Valves- Ball
OPEN
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CLOSED
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Types of Valves- Ball
Advantages:
Low pressure drop when open.
Can be used for gas, liquids or slurries, high Pressure & temp
Open and close quickly and easily.
Require no lubrication.
Are suitable for handling corrosive fluids
Provide leak proof service when dirt or abrasion not present .
Disadvantages:
Standard Ball Valve not suitable for regulating flow.
Not suitable for tight shut-off when dirt or abrasion present.
Can be damaged & jammed by solids.
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Types of Valves- Plug
• The plug is tapered and has
transverse ports which match
similar openings in the valve body.
The body is machined for the
tapered plug to fit.
• The valve moves from fully open to
fully close in a quarter of a turn.
• Grease is forced around the plug
to act as a seal and lubricant.
• It is primarily, for on/off service.
• It consists of a body, a plug and a
cover.
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Types of Valves- Plug
Note: Materials of construction are cast iron, steel and stainless steel,
bronze, nickel and many corrosion resistant alloys.
Temperature rating for lubricating type valve is up to 400deg C.
Sizes vary from ¼” to 16”
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Types of Valves- Plug
Advantages:
Cheap, simple design with few parts
Offer low resistance to flow when fully open
Open and close quickly, easy to operate
Give a tight seal with pressures up to 200 bar
Provide leak-proof service
Disadvantages:
The plug valve is mainly an on/off valve and is not particularly good for
precise regulation
Despite lubrication, the plug valve has a tendency to bind (stick)
Costlier than ball valves
Due to high friction, 1st movement(opening-closing) requires a large
amount of force
Larger valves require a gear box or an actuator
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Types of Valves- Diaphragm
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Types of Valves- Diaphragm
Advantages:
Fairly cheap and easy to make
Provide good flow regulation, opening and closing
Maximum wear is located at the diaphragm which is easy
to change
Provide good chemical resistance
Disadvantages:
X Cannot be used for large size valves
X Cannot be used at very high pressures & temperatures,
due to the weakness of the diaphragm
X They produce a pressure drop when open
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Types of Valves- Needle
Needle valves are used
to give fine, accurate
control of flow.
The 'needle' shaped
closing element is long
and comes to a point.
The seat is also very
small.
The stem threads are
close together (a fine
thread) which makes
very small adjustment of
the flow possible.
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Types of Valves- Needle
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Types of Valves- Needle
Advantages:
Suitable for regulating flow.
Fine control in small diameter piping.
Tight shut-off.
Disadvantages:
X Only for clean fluids.
X Can only be used with very low flows rates.
X High pressure drop when open.
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Types of Valves- Butterfly
• A butterfly valve consists of a disc,
sometimes called as a vane or a flapper, a
shaft and a body. The shaft is supported on
bearings and is sealed with some form of
packing.
• Butterfly valves are normally used in control
situations where tight shut-off is not required.
• They can be manually operated, but often
they are operated by some form of actuator.
• These valves consist of a circular disc turning
on diametric axis of the valve body.
• These were not really leak tight valves and
needed considerable application of torque for
operation. On account of this deficiency the
application of these valves was limited to; use
as dampers in ducting systems and in low
pressure water systems.
.
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Types of Valves- Butterfly
WAFER TYPE
BUTTERFLY
VALVE
OPEN
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CLOSED
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Types of Valves- Butterfly
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Types of Valves- Butterfly
Advantages:
The valve can be part open in any position from fully
closed to fully opened.
Fast operation - the valve moves from full close to full
open in a quarter of a turn.
The handle shows if the valve is open or closed.
They can receive flow from both sides.
Less number of parts
Disadvantages:
X Can only be used with low flows rates.
X Not suitable for tight shut-off.
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Types of Valves- Angle Valve
In an angle valve the
inlet and the outlet
ends are at 90 deg. to
each other and the
axis of the stem is in
line with one of the
ends.
In
comparison
to
globe valves angle
valves have lower
pressure drops and
they also reduce the
number of fittings in
the piping system.
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Types of Valves- Angle
Advantages:
Flow direction can be changed
Can be used for high pressure drops.
Elimination of an elbow, should one be required.
Has little restriction on the out flow, so if flashing or
cavitation occurs then it tends to do so further
downstream from the valve
Used for erosive applications
Disadvantages:
X When open pressure drop is seen.
X More parts.
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Types of Valves- Check Valves
Check Valves or Non Return Valves (NRV)
Non Return Valves (NRV) or Check Valves only allow
flow in one direction.
There are several different designs.
The following slides show the three main types:
• BALL CHECK VALVE
• SWING CHECK VALVE
• LIFT CHECK VALVE
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Types of Valves- Ball Check Valve
Ball Check Valve
OPEN
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CLOSED
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Types of Valves- Swing Check Valve
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Types of Valves- Swing Check Valve
Swing Check Valve
OPEN
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CLOSED
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Types of Valves- Lift Check Valve
Lift Check Valve
OPEN
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CLOSED
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Types of Valves- Check Valve
Advantages:
They open and close automatically. They do not need
external force to open and close. They move quickly
Flow is in one direction and does not allow reverse
flow.
Disadvantages:
X Valve discs can get stuck in open position
X Check valves have restrictions during assembly
X It is hard to determine if the valve is open or closed,
as all the moving parts are inside.
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Types of Valves- PSV
Pressure Safety Valve (PSV)
• Pressure Relief Valves (PSV) are used in process
applications to relieve excess pressure in the system when
damage could occur.
• All closed vessels where pressure could build up are
protected by a PSV.
• An important part of the relief valve installation is the
routing of the relieved fluid or gas – Normally relieved fluid
is returned to a service tank or an unpressurised part of the
system.
• Gases could be vented to a suitable vessel but are
generally vented to the flare system.
• Over pressure steam will be vented to atmosphere
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Types of Valves- PSV
Pressure Safety Valve (PSV)
• The PSV seat is held in place by a large spring, the
resistance of this spring will determine the pressure needed
to lift the seat and allow flow. The spring resistance is
adjusted by a screw fitting that compresses or releases the
spring and should only be adjusted by competent person as
this adjusted will be tested and recorded.
• If a PSV lifts and vents due to over pressure, it should
reseat and seal once again after the pressure has dropped
below its lifting set point, if it does not, it will need to be
reset in a workshop by a technician.
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Types of Valves- PSV
Pressure
Safety
Valve
(PSV)
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Types of Valves- PSV
Pressure
Safety
Valve
(PSV)
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Types of Valves- PSV
Pressure
Safety
Valve
(PSV)
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Types of Valves- PSV
Pressure
Safety
Valve
(PSV)
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Types of Valves- PSV
Pressure Safety Valve (PSV)
• Valves used for safety applications require regular
inspections to check the settings and the operation.
Records of testing schedules and results must be kept
in a central database, this is usually done during a
shutdown.
• All PSV’s have their own unique serial number
because each PSV is rated for the design pressure
and volume of the specific piece of equipment it is
protecting.
• PSV’s are constructed to be very robust and strong,
due to the nature of their function, they may be
subjected to rapid changes in temperature, flow and
of course pressure, in a very short space of time
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Types of Valves- PSV
Pressure Safety Valve (PSV)
• PSV’s should only be Isolated if an alternative
pressure safety system is available (spare PSV)
or if the vessel it is protecting, is not in service
and depressured.
• PSV settings will always be below the safe
design pressure of the vessel it is protecting.
• If plant equipment is upgraded, it is important to
upgrade the PSV capability in line with the new
vessel, for both pressure and flow ratings.
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Types of Valves- PSV
Advantages:
Can be used in wide range of chemical processes
Can be used for high pressure and temperature
Pressure release is in one direction and does not allow
reverse flow.
Disadvantages:
X
X
X
X
Prone to leakage if spring/bellows does not reset properly
Relieving pressure affected by back pressure
Fouling fluids can create valve malfunctioning
Chattering may occur.
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Types of Valves- PSV
Pressure Safety Valve (PSV)- Bursting Discs
• A bursting disc is
a non re-usable
device
that
is
designed to burst
or rupture at a set
pressure,
thus
protecting process
equipment
from
high pressure or
vacuum
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Types of Valves- PSV
Pressure Safety Valve (PSV)- Bursting Discs
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Types of Valves- PSV
Pressure Safety Valve (PSV)- Bursting Discs
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Types of Valves- Bursting Disc
Advantages:
Can be used in corrosive, chemical services
Less tendency to foul or plug
Can be used in low pressure and normal temperature
services.
Disadvantages:
X
X
X
X
Don’t reclose after relief
Burst pressure can not be tested
Greater sensitivity to temperature
Easy to get damaged.
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Quiz
1. Name these valves.
2
3
1
2. Where are PSV’s used and what does it stand for?
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Quiz
3. What 4 variables can a valve control?
4. Name 3 valves that can be used for throttling flow?
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Quiz
5. Name one valve that rarely operates when in
service?
6. Name 3 valves that can prevent non return of a fluid
down a pipeline?
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