INFORMATION SHEET

MODULE 7: VALVES

VALVES

Introduction:

Valves are extensively used in piping systems and on equipment to which piping is connected.
Some valves are used continuously, others intermittently, and some, like safety values, are
utilized only in rare instances.

Function of Valves:
Function of Valves is to start, stop or regulate a flow of liquid or gas through a plant system.
This is accomplished by maintaining the valve in a partially open position or an open or closed
liquid or gases flow from areas of higher pressure to areas of lower pressure because there
control of flow is of high importance. Mechanical devices that are used in industrial piping for
flow control are called valves. The term Valves includes all equipment that acts on the
movement of fluid by one of the following two functions:

1. Opening or closing a circuit.

2. Controlling of flow.

The fluid may be liquid, gas or a loose solid such as powder, sand of slurry.

When a valve allows some flow, but not maximum flow it is said to be in the THROTTLING
position to Throttle with a valve is to regulate the (Rate or direction) flow. (Figure 1)

Valve Classification and Types:

Valves can be classified by
Function.
Disc arrangement.
Operating condition such as temperature and pressure, or by the way they are
incorporated into plant systems.

The most common way to classify a valve is by the arrangement or shape of the disc, which is
part of the valve that controls the flow of fluid through the valve.

Gate,
plug,
ball, or
MET 104- MATERIAL TECHNOLOGY 1
 INFORMATION SHEET
MODULE-7: VALVES

Butterfly valves are most widely used for the interruption or start of flow.
Diaphragm valves may be preferred in corrosive applications or in service where
contamination of the fluid is not permissible, such as in the drug and beverage
industry.

Construction:
a- Figure 1 shows the basic construction of a common valve type, namely a stop valve, and
shows the principle of operation
b- Fluid flows into the valve through Inlet Port through the passages in the valve body
past the element that controls the flow, and then flows out via the Out let or Discharge port
c- If the closing element (named a disc) in the close position the passage way is blocked and
no fluid can flow until it is opened again.

Figure 1 Valve Components

2 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

Materials:

Valves are subjected to the effects of heat, pressure and corrosion, so it is important that they are
made from appropriate materials. That can be made from:
Bronze
Cast iron
Steel
Stainless steel
Monel
Brass and other metals as well as from plastic and glass.
Valves are usually made to the some standards and specifications of the pipe work I the
system. They also come in a large variety of sizes.

Fluid-control elements inside the valve include:

seat,
disc,
plug, or ball
stem or spindle,
Sleeves needed to guide the stem and disc.

These elements are also called the trim. The disc/seat interface and the relation of disc position
to seat determine valve performance to a large extent.

Figure 2 How a valve operates

MET 104- MATERIAL TECHNOLOGY 3

 INFORMATION SHEET
MODULE-7: VALVES

Valve Components:
1. Valve body: is the largest structural part of the valve. It provides the means for
attaching the valve to the system components or piping.
2. Seating Area: is located inside of the valve body. This is the area where the disc
closes on the valve body seat. The disc and seat must be smooth, and must fit
together perfectly.

The seat can be

a. Threaded
b. Press-fit
c. Welded into the body
d. Cost as part of the valve body.

In high temperature, high pressure system, a combination of threading and welding is used to
prevent leakage between the valve body and the seat.

Materials used for seat construction

For low-pressure low temperature system valve seat may be made of bronze or Teflon type
material.
For high pressure & temperature the seat area must be very strong same as stellite.
3. Disc is the part of the valve that closes against the seat to stop flow.
4. Stem is connects the disc to the hand wheel. The stem transmits the motion of the
hand wheel to the internal disc open & closes the valve ways

Disc attached to the stem:

In slip-type joint
Threading is another method
Stem & Disc manufactured as one piece
5. Bonnet: is attached to the valve body by bolting, threading, or welding.
6. Stuffing box: is filled with a packing to prevent leakage.
7. A packing gland: Is to hold and compressed the packing in place to prevent leakage
by the stem and through the bonnet.
8. Hand wheel or Actuator: controls the movement of the disc inside the valve. A hand
wheel is generally turned manually, while an actuator is controlled by an electric,
pneumatic, or hydraulic motor.
9. Bridge wall markings: is providing useful information indicates how the internal parts
of the valve are arranged, will show the direction of flow.
10. Service markings: indicates the maximum allowable pressure service the letters W,
O, or G on the valve body indicate the type of service the valve is designed for.
4 YANBU INDUSTRIAL COLLEGE
Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

VALVE ACTUATOR SUMMARY

Manual actuators are the most common type of valve actuators.

Electric motor actuators consist of reversible electric motors connected to the valve stem
through a gear train that reduces rotational speed and increases torque.
Pneumatic actuators use air pressure on either one or both sides of a diaphragm to
provide the force to position the valve.
Hydraulic actuators use a pressurized liquid on one or both sides of a piston to provide
the force required positioning the valve.
Solenoid actuators have a magnetic slug attached to the valve stem. The force to position
the valve comes from the magnetic attraction between the slug on the valve stem and the
coil of the electromagnet in the valve actuator.

Gate Valves

Gate valve the disc arrangement is not designed to control the rate of flow. Its used for isolation
or for on or off unable to throttle.

Normally, gate valves are placed where straight free flow is desired and where an immediate shut
off of flow may be necessary.
Often described simply as a GATE, this type of valve has a gate that goes up and down in
the body, integral with a stem ending in screw thread on which the hand wheel is
screwed. The hand wheel rotates freely at fixed height, so that their rotation causes
vertical movements of the stem or the gate depend on the stem type.
The gate valve is used exclusively on lines for liquid.
In a gate valve, the disc is wedge-shaped with mating surfaces on two sides. These
mating surfaces close against the seats to stop the flow of fluid.
Bodies of gate valves, whether small or large, can take the form of two intersecting
cylinders, with one for the fluid flow and the other to house the raised disc. Fig.3

MET 104- MATERIAL TECHNOLOGY 5

 INFORMATION SHEET
MODULE-7: VALVES

Figure 3 Gate Valve

Gate Valve Construction:

The exterior construction of most gate valves is similar.

The body houses the fluid, and the bonnet acts as a lid for the body. The actuator (a hand
wheel, for example) opens and closes the valve.
The interior construction of gate valves varies, depending on the type of valve and the
manufacturing design.

6 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

Many valves are equipped with a neck bushing, or stem bushing, to act as
guide for the stem and to form the bottom of the stuffing box. The threaded
STEM
end of the stem, screws through the stem, bushing, the hand wheel and the
BUSHING
stem bushing are solidly connected, thus raising or lowering the stem when
the hand wheel is turned.
BODY Main part of the valve directly attached to the pipe.
FLANGED Part of the body with bolt holes to allow the connection with the flanges set
ENDS on the pipes.
GASKET Inserted between pipe and valve to have a tight, leak proof connection.
BONNET Part of the valve mounted on the top of the body to form a tight enclosure.
YOKE Part of the valve to support the hand wheel and bushing.
Solidly connected to the gate, the rotation of the stem raise or lowers the
STEM
gate.
The operator is used to control the stem, which moves the disc up and down
HAND WHEEL
to control the flow of fluid through the valve.
GATE Is the part of the valve that controls the opening.
When the gate is lowered, the seat rings fit with the gate to stop all flow.
SEAT RINGS

Every valve with a stem has (STUFFING BOX) to ensure the sealing
STUFFING BOX
between the fluid and the atmosphere.
Special material (made of asbestos, grease, neoprene each manufacturer
specifies a given type and size of packing for each stuffing box) used to fill
PACKING
the stuffing box.

After the packing is installed the gland compresses the packing, the gland
also serves as the stuffing box covers. Packing is installed in the stuffing
GLAND
box to control the flow of fluid along the stem. The packing is held in place
and compressed by the gland follower.
In order to permit re-packing under pressure, some valves are equipped with
BACKSEAT a back seat. The back seat is a tapered restriction which mates with a
widened section on the stem to stop the flow of fluid along the stem.
The bonnet gasket is provided to eliminate leakage between the bonnet and
BONNET
body. The yoke acts as a support for the stem, and has a stem nut that raises
GASKET
and lowers the stem.

MET 104- MATERIAL TECHNOLOGY 7

 INFORMATION SHEET
MODULE-7: VALVES

RISING and NON RISING STEM

Figure 4a Rising Stem Figure 4b Non-rising stem gate valve

Up to a steam working pressure of 250 psig, gate valves are usually made with an oval bonnet
flange to reduce the face-to-face dimension. In the valves designed for higher pressures, a bonnet
flange or circular shape is preferred to provide a recessed gasket joint.

Globe Valves
The Globe valve can be used as a regulating valve, or as a stop valve for isolating systems. If it is
used for regulation it is often called a control valve.

Figure 5 Components of Globe Valve

8 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

The change in direction of the fluid as it flows through the valve results in increased resistance to
the flow.

Figure 6 Variation of basic valves as to design

Also owing to the construction of the valve, a globe valve is recommended when the valve is to
be operated frequently. The disk in a globe valve touches the seat only at the instant of closing.
In a gate valve, the wedge travels over the full face of the seat and consequently sliding wear will
develop.

DESIGN FEATURES

Globe valves are constructed in several ways:

BALL - SHAPED DISC

This disc fits on a tapered, flat surfaced seat and is usually used on relatively low pressure, low
temperature system Fig 7. Its generally used in a fully open or shut position, but may be for
moderate throttling.

MET 104- MATERIAL TECHNOLOGY 9

 INFORMATION SHEET
MODULE-7: VALVES

Figure 7 Ball Shaped Disc Figure 8 Composition Disc

THE COMPOSITION DISC

This disc is renewable and can be adapted to varying types of flow. The seating surface is often
formed by a rubber O ring or washer. Fig. 8
THE PLUG-TYPE DISC
This disc is also renewable, along with its seat rings and is very useful for heavy duty throttling.
Disc is cone shape and it fits into a cone shaped seat. Fig.9

Figure 9 Plug-Type Disc

10 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

THE NEEDLE DISC

This disc which is very narrow and, therefore, best suited for close regulation of flow. The
diameter of the seat opening is very narrow, and the disc descends well below it and into orifice
formed by the seat. Fig.10

Figure 10 Needle Valve

BACK SEATING
Many globe valves used for steam service are built with a back seat. A back seat is a seating
arrangement that provides a seal between the stem and the bonnet. when the valve is fully open.
Fig. 11

Figure 11 Back Seat Design

MET 104- MATERIAL TECHNOLOGY 11

 INFORMATION SHEET
MODULE-7: VALVES

The back seat design prevents system pressure from building against the valve packing. In its
fully open position, the back seat of the disc prevents leakage into the upper part of the valve.

Plug, Ball & Butterfly Valves

Plug, Ball and Butterfly valves are distinguished from other types of valves by the fact that they
are not made with discs that rise and descend from the valve seating area.
These valves design not to provide the same tight sealing as a globe valve. The seats are often
made of plastic coated, self- lubricating. The disc on these valves opens by rotation. When the
valve is actuated the disc makes a one-quarter turn, to close or open the part. Plug & Ball Valves
can be constructed with more than one part for flow through the valve.

1. PLUG VALVE (COCK)

Plug valves, also called cocks, generally are used for the same full flow service as gate valves,
where quick shut-off is required. They are used for steam, water, oil, gas, and chemical liquid
service.

Many differences in design and detail adapt the valve to various services. Variations on the basic
concept can borrow from other types of valve, too.
Flow resistance is low if the port. The plug valve can throttle on moderately demanding services.
Its plug has two orifices, which helps in breaking down high pressure drops.

Figure 12 Plug Valve

12 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

2. BALL VALVES
In the past, the use of ball valves 1 has been rather limited as bubble tight service was
not possible because of problems in the sealing ability of metal-to-metal seats.
In recent years, the use of plastics, such as nylon, delrina, synthetic rubbers, and
fluorinated polymers for seating, has substantially increased the use of ball valves.
With fluorinated polymer seats, ball valves are used for service temperatures ranging
from 450 to 500 F. With graphite seats, temperatures as high as 1000 F are possible.
Ball valves, similar to plug valves, are quick opening, needing only a quarter turn from
full open to full close.

To open the valve, the ball is rotated so that the through port lines up with the seat openings.
When the valve is closed, line pressure forces the ball against the downstream seat, in an action
similar to that of a gate valve.
Ball valves are non-sticking,
They provide tight closure.
They also exhibit a negligible pressure drop because of their smooth, full-opening port.
These valves are easy to repair, and maintenance costs are low.

Major components of the ball valve are:

body,
spherical plug,
seats.

Ball valves are made in three general patterns venturi port, full port, and reduced port. The full-
port valve has an inside diameter equal to the inside diameter of the pipe. The reduced port
generally involves one pipe size smaller than the line size. Stem sealing is by bolted packing
glands and O-ring seals.

Open Closed
Figure 13 a. Ball valve

MET 104- MATERIAL TECHNOLOGY 13

 INFORMATION SHEET
MODULE-7: VALVES

Figure 13 b. Ball valve components

The seats of these valves are often made for plastic coated or self-sealing materials. Although
providing a good seal at low pressures, they are not usually found in high pressure steam
systems. They are very good in systems carrying dirty materials such as mud or slurry. Another
advantage is that fluid can flow through the valve in either direction.

3. BUTTERFLY VALVES
Butterfly valves of extremely simple design, which are used to control and regulate
flow.
They are characterized by fast operation and low differential pressure drop.
They required only a quarter turn from closed to full open position.
Butterfly valves are not intended for pressure-tight service. A typical flanged butterfly
valve is illustrated in Fig 14
The disc is attached to the stem, and used primarily for isolation of flow. In addition to
shut off function, butterfly valves can be used for throttling application not frequently
because poor throttling characteristics. The disc is always the same diameter as the
piping on which the valve is attached.

14 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

Figure 14 Typical butterfly valve and part details

The position of the butterfly valve disc can easily be seen. The operating lever is in line with the
pipe when it is open and perpendicular or across the pipe when closed. This is also usually the
case with plug and ball valves

4. Diaphragm Valves
Most valves depend on a controlled geometry and rigid materials for closure.
The diaphragm valve operates on an entirely different basis:
A highly flexible and extensible Elastomer sheet forced down into a rigid edge,
The seat, causes closure.
If the valve body, including the seating area, is rigid plastic or a metal with corrosion-
resistant Elastomer lining,
The diaphragm valve has an important potential advantage - high resistance to
corrosive liquids.
This is its chief application, naturally, in water-treatment work and for liquids that might be
contaminated by metal contact.

Figure 15 typical diaphragm valves

MET 104- MATERIAL TECHNOLOGY 15
 INFORMATION SHEET
MODULE-7: VALVES

Check Valves
A satisfactory check valve should therefore: open easily and completely to pass flow with little
pressure drop or disturbance to flow patterns; resist damage to seat disc and disc hanging or
guiding means in all flow conditions during valve life; close quickly, without valve injury or
water hammer, at the instant or flow stoppage. This adds up to a demanding design effort, and
success has been sporadic.

Check Valves Design and Type:

1. Swing Check
2. Lift Check
3. Ball Check used to prevent back flow.

Swing Check Valve:

The only moving part is a disc assembly that is attached to the body by a pivot pin. The disc is
raised when system pressure is greater than the weight of the disc. Fig. 16 used mainly in
horizontal piping.

Figure 16 Swing Check Valve

Lift Check Valves:

Lift check valves used in horizontal and vertical piping good for high pressure and velocity. The
line of flow through a lift check valve is similar to the line of flow through globe valve. The
direction of the flow is always from under the disc. Fig.17. The lift check valve allows flows in
only one direction. When flow occurs from A to B, it raises the disc. As flow stops, gravity pulls
the disc into the seating, and the back flow assist also.

16 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

Figure 17 Lift- type check Valve

Ball Check Valves:

The ball valve is also a check valve used mainly for heavy liquids. The line of flow through such
a valve is in a straight line. The part of the valve that controls the opening is a ball. When flow
occurs, the ball is raised by the pressure of the flow.

Figure 18 Ball Check Valve

Automatic Control Valves:

Control valves can be operated pneumatically, hydraulically, or electrically. The actuator on each
type is designed differently. All generally have a manual backup.

1. Pneumatically Operated Control Valve

The actuator of a pneumatically operated control valve consists of a pneumatic line,
diaphragm, and spring.
The pneumatic line (also called an airline) conveys compressed air to provide the
pressure for moving the stem of the control valve.

MET 104- MATERIAL TECHNOLOGY 17

 INFORMATION SHEET
MODULE-7: VALVES

The diaphragm provides a broad surface on which the air pressure can act. The
diaphragm presses against the top of the valve stem, and moves the stem in
response to the air pressure.
The spring provides a force that the air pressure must overcome in order to move
the valve. The actuator design dictates whether the spring holds the valve open
or closed.

Figure 19 Pneumatic Control System

2. Hydraulically Operated Control Valve

The actuator of a hydraulically operated control valve consists of an actuator valve,
hydraulic lines, and piston
A small actuator valve (not shown) directs the hydraulic fluid to one side or the
other of the piston.
Depending the actuator valve's position, the hydraulic fluid drives control valve
toward either the fully open or fully close position.
Hydraulic lines are used to carry the hydraulic fluid to side of the piston.
The hydraulic fluid acts against the piston to position control valve.

3. Electrically Operated, Remotely Controlled Valve

There are two types of electrically operated, remote] controlled valves: motor-driven and
solenoid-actua1
MOTOR-DRIVE VALVE, Where a reversible electric Motor-driven valve
generally consists of an electric and a reduction gearbox.

18 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

Figure 20 Motor-driven Valve

4. SOLENOID-ACTUATED CONTROL VALVE

The solenoid-actuated control valve consists of a wire iron core, and spring.
The wire coil carries an electric current that generates magnetic field. The iron
core is moved through the will coil by the magnetic field.
The iron core is attached to the valve stem. When the iron core is moved through
the wire coil, the valve opens or closes, depending on the design.
The spring opposes the motion of the iron core and when the electric current is
removed, returns the valve to the closed position.

Figure 21 Solenoid-actuated Control Valve

MET 104- MATERIAL TECHNOLOGY 19

 INFORMATION SHEET
MODULE-7: VALVES

Pressure Relief Valves:

Principal Types of Pressure Relief Valves:

Pressure relief valves are designed to protect a pressure system against excessive normal or
subnormal pressure in the event of positive or negative excursion of the system pressure.
They are required to open at a predetermined system pressure, to discharge or let enter a
specified amount of fluid so as to prevent the system pressure from exceeding a specified
normal or subnormal pressure limit, and to re-close after the normal system pressure has been
restored.
Pressure relief valves must also be self-actuated for maximum reliability except where
permitted by the applicable Code of Practice for specific applications.

1. Safety Valves
Safety valves, such as those shown in Figure 22, are intended primarily for the
relief of steam in industrial boiler plants and other steam systems.
To provide this protection, safety valves are commonly provided with an open
bonnet that allows steam leaking into the bonnet to escape directly into the
atmosphere around the valve.

Figure 22 Safety Valves

20 YANBU INDUSTRIAL COLLEGE

Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

2. Safety Relief Valves

Safety relief valves are general-purpose pressure relief valves for use in either gas or
liquid service as encountered in the process industry.
Because the fluids handled in these industries cannot normally be tolerated to escape
around the valve, the bonnet of these valves is either vented to the valve outlet or
sealed against the valve chamber by means of bellows.
An exception is safety relief valves for process steam duty in which the bonnet is
provided with windows as in safety valves.
The industry distinguishes between conventional safety relief valves and balanced
safety relief valves.

Figure 23 Safety Relief Valves

MET 104- MATERIAL TECHNOLOGY 21

 INFORMATION SHEET
MODULE-7: VALVES

VALVES APPLICATIONS SUMMARY

Value type General application Actuation Remarks
Usually manual, but maybe: Usually applied to higher pressure
Shutt-off regulation of
Electric or high volume systems, due to
Globe valve liquid/gas flow. Steam and
Hydraulic cost. Less suitable for viscous or
condensate applications.
Pneumatic contaminated fluids.
Used fully open or fully
closed for an/off regulation Usually manual, but maybe: Usually used where the valve
on steam, gas and other Electric body is to be permanently
Piston valve
fluid services. Typically Manual installed and maintenance needs
used on fluids that cause Hydraulic to be minimized.
excessive seat wear.
Normally used fully open or Not recommended as a throttling
Usually manual, but maybe:
fully closed for an/off valve. Solid wedge gate is free
Electric
Gate valve regulation on water, oil, from chatter and jamming.
Manual
gas, steam and other fluid Parallel slide valve used in steam
Hydraulic
services. systems.
Shut-off and regulation in Handwheel Relatively simple construction.
lager piplines in Electric motor Can be produced in very large
Butterfly
waterworks, process Pneumatic actuator sizes. Eccentric design essential
valve
industries, HPI, power Hydraulic actuator for steam systems. Typically used
generation Air motor on liquid systems.
Wide range of application in Handwheel
all sizes, including HPI, Electric motor Can handle all fluid types. Limited
Ball valve
steam and condensate Pneumatic actuator maximum pressure rating.
application Hydraulic actuator

PREVENTIVE MAINTENANCE

1. Inspection
Intervals of inspection vary from valve to valve. Type of valve, quality of water being
handled, rates of flow, operating pressures, and past maintenance practices all have a
bearing on the length of service between overhauls.
Periodic inspections in order to check for proper valve operating pressures.
Visual leaks for any external leakage; any abnormalities in the operating pressures
resulting from the operation of the valve, the valve should be scheduled for service.

2. Every Two (2) Months:

Flush the strainer via the flushing cock.
22 YANBU INDUSTRIAL COLLEGE
Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

Visually inspect for leaks around the indicator rod, bottom cap/differential vent hole, or
pilot valves (hydraulic & /or solenoid).

3. In-Service Inspection:
Valves are inspected while in service to determine if the components function properly
under routine operating conditions.
When inspecting a valve, it may be necessary to perform minor adjustments, such as
adjusting the packing or the operator, to keep the valve in good operating condition.
Particular attention should be given to the stuffing box and flanges to check for leaks in
the packing or gaskets.
When defects are found that cannot be corrected immediately, they must be reported so
that necessary action can be taken.
Internal Leakage in valves: The major problem in determining valve leakage is
determining whether the suspect valve is the only source of pressure or fluid. Therefore,
a good knowledge of the system is essential for isolating the suspect valve.

Reasons for Maintenance

Failure or loss of efficiency.
Stem leaks;
stem binding,
improper operator adjustment,
leaking while the disc is closed against the seat,
Leaks in flange mating surfaces, or other defects.

4. Troubleshooting
Common Symptoms
Valve will not respond to signal.
Sticky Valve
Sluggish Valve
Jumpy Valve
Rotary valve does not rotate

MET 104- MATERIAL TECHNOLOGY 23

 INFORMATION SHEET
MODULE-7: VALVES

Valve Troubleshooting Table

Possible
Possible Causes Corrective Action
Problem
Gaskets Replace
Leakage

Packing Adjust or replace

Loosen Bolts ( Bonnet, Flange Packing) Retighten
Repair by welding or
Groove in Flange
replace
Seat Repair or replace
Passing*
Disc Repair or replace
Packing over tight loosen
Thread Rethread and clean
Dirt & Scale Clean
Incorrect flow direction Correct flow direction
Stem damaged by improper maintenance procedures Replace
Piping and valve flanges are misaligned Reinstall valve
Gasket degradation due to exposure to high Replace with compatible
temperature materials
Bent or damaged shafts/stems resulting in sticking or
Disassembly and repair
binding
Disassembly and repair.
Plug and cage galling from overheating or selection of
Replace with compatible
incompatible materials
Hard to operate

trim.
Stem and guide bushing galling Disassembly and repair
Grit, debris, or welding slag preventing proper plug Disassemble, clean, and
movement repair
Buildup of viscous, sticky, or coking fluids impeding Select compatible valve
plug movement style
Undersized actuator Replace
I/P calibration underranged Calibrate
Incorrect flow direction Correct flow direction
Install stiffer spring or
Undersized actuator
larger actuator
Bent, galled, or missing components interfering with
Disassembly and repair
proper operation
Plug frozen by debris between plug and cage, stem and
Disassembly and repair
bushing, or plug and seat
Excessive actuator force has welded plug into seat Disassembly and repair
Plug slamming (from dynamic instability) has welded Check flow direction, valve
24 YANBU INDUSTRIAL COLLEGE
Educating Technologies
INFORMATION SHEET
MODULE 7: VALVES

plug into seat type, valve ratings

Replace sticking
Galling caused by high temperature components with
compatible components
Welding slag introduced during installation or during
Disassemble, clean, and
subsequent upstream retrofit or maintenance has
repair
bound components
Mechanical obstruction to plug movement, e.g.: Disassemble, clean, and
welding slag, pipeline debris repair
* Internal leakage

MET 104- MATERIAL TECHNOLOGY 25