Valves
-
Upload
brahim-letaief -
Category
Documents
-
view
5 -
download
0
description
Transcript of Valves
-
Unauthorized Reproduction of Learning Material Is Prohibited!
BP CASPIAN SEA VALVES
VALVES (MD-023)
Copy No:
QC Check:
-
REV 1: Valves (MD-023) Page 2 of 42
REVISI0N HISTORY Revision Number Date Comments Rev: 0 29-07-2004
Rev: 1 03-11-2004 Signed off by Douglas Milne 06-11-04 ISSUE 1
-
REV 1: Valves (MD-023) Page 3 of 42
TOPICS COVERED INCLUDE
Factors affecting valve selection
Pressure Drop
Flow Regulation
Shut Off Capability
Erosion
Corrosion
-
REV 1: Valves (MD-023) Page 4 of 42
CONTENTS
VALVES (MD-023)
1. INTRODUCTION
2. HAZARDS ASSOCIATED WITH VALVES
3. IDENTIFY VALVES & DESCRIBE THEIR FUNCTIONS
4. MAJOR VALVE PARTS
4.1. BODY
4.2. OPENING ELEMENT
4.3. STEM
4.4. HANDWHEEL / HANDLE
4.5. BONNET
4.6. PACKING GLAND
5. TYPES OF VALVES AND THEIR FUNCTIONS
5.1. BUTTERFLY VALVE
5.2. GLOBE VALVE
5.3. BALL VALVE
5.4. GATE VALVE
5.4.1. RISING STEM
5.4.2. NON RISING STEM
5.5. PLUG VALVE - FIGURE 11
6. AUTOMATIC VALVES & THEIR FUNCTION
6.1. CHECK VALVES (NON RETURN VALVES N.R.V )
6.1.1. SWING CHECK VALVES FIGURE 12
6.1.2. BALL CHECK VALVE - FIGURE 13
6.2. FUNCTION OF CHECK VALVES FIGURE 14
-
REV 1: Valves (MD-023) Page 5 of 42
6.3. NEEDLE VALVES - FIGURE 15
6.4. SAFETY RELIEF VALVE
7. THE OPERATION VALVES
7.1. MANUAL OPERATION
7.1.1. HANDWHEEL OPERATION
7.1.2. HANDLE OPERATION
7.2. LOCAL OPERATION
7.3. REMOTE OPERATION
7.4. AUTOMATIC OPERATION
7.5. LOCAL AUTOMATIC OPERATION
7.6. REMOTE AUTOMATIC OPERATION
8. VALVE ACTUATORS
8.1. ELECTRIC MOTORS
8.2. PNEUMATIC ACTUATORS
8.3. HYDRALIC ACTUATORS
8.4. SOLENOID / MAGNETIC ACTUATORS
9. GLOSSARY
-
REV 1: Valves (MD-023) Page 6 of 42
VALVES (MD-023)
1. INTRODUCTION
The most common mechanical device used in process operations is the
valve. Valves are used to control the flow of liquids and gases in piping
systems.
A wide range of products, pressures, and temperatures are used in
processing systems, so valves are made in a wide range of types, shapes
and materials.
-
REV 1: Valves (MD-023) Page 7 of 42
2. HAZARDS ASSOCIATED WITH VALVES
Valves are used to minimise the hazards associated with the transfer of fluids
by providing methods of controlling or isolating the pressure and flow of fluids,
It is mainly when valves fail that hazards arise, depending on the chemical
and physical nature of the fluid being handled.
Often the failure of a valve will go unnoticed as they are situated within the
pipe where their operation cannot be seen. Extra precautions should be taken
when performing tasks that rely on the correct operation of a valve.
For example, when pipelines are being dismantled for maintenance, any
isolating valves in the system must be closed and if possible, the pipeline
drained. Adequate safety equipment should be worn and pipelines opened
slowly to prevent large amounts of fluid leaking out in the event of an isolation
valve failure.
Any valve that is stuck should not be forced open as this may cause fluid to
leak out past the stem and onto operators. Any valves that are known to be
leaking, either internally or externally, should be reported and changed as
soon as possible.
Any unusual trends in valve operation should also be reported but no
adjustments should be made without prior consultation with senior personnel
and investigations carried out to discover the reasons for the unusual trend.
-
REV 1: Valves (MD-023) Page 8 of 42
3. IDENTIFY VALVES & DESCRIBE THEIR FUNCTIONS
Different types of valves perform different functions. Some are used to start
or stop flow in pipelines. Other valves are used to regulate flow in pipelines.
Figure 1 Open and Closed Valves
The element changes position to open and close the valve.
Body
Stem
Valve
Seat
Inlet
Handwheel
Closed Open
Opening
Element
-
REV 1: Valves (MD-023) Page 9 of 42
Figure 2 Common Valve Parts
Handwheel Nut
Bonnet
Handwheel
Packing
Packing Gland
Body
Valve Seat
Opening Element
Stem
-
REV 1: Valves (MD-023) Page 10 of 42
4. MAJOR VALVE PARTS
4.1. BODY
The body is the part of a valve that is attached to pipes. The gases or liquids
flow through the body when the valve is open.
4.2. OPENING ELEMENT
This is the part that opens and closes the valve. All valves have an opening
element in the valve body. Opening elements are made in various shapes
and sizes. They can move up and down on a stem, or rotate around a central
pivot point.
The opening element stops or allows flow through a valve. We will discuss
types of opening elements further when we look at different types of common
valves.
When the valve is closed, the opening element fits against the valve seat.
4.3. STEM
The stem raises or lowers the opening element. In manually operated valves,
the steam is usually threaded. In ball valves and butterfly valves, the stem
does not go up or down. It turns inside the bonnet. In pneumatic and
hydraulic valves, the threaded stem is replaced by a smooth rod that moves
up and down in the valve.
-
REV 1: Valves (MD-023) Page 11 of 42
4.4. HANDWHEEL / HANDLE
On a manual valve, a hand wheel or handle is attached to the stem. The
hand wheel or handle allows the operator to turn the stem. The hand wheel is
held on the stem by the hand wheel nut.
4.5. BONNET
The bonnet is a separate housing that is bolted tightly to the top of the valve
body. The stem passes through the bonnet. The bonnet holds the stem in
position.
4.6. PACKING GLAND
The packing gland is held in place by bolts, or sometimes it is screwed into
place. This gland keeps the packing tight. Packing is a soft material inside
the bonnet, placed around the stem to make a tight seal. The packing keeps
pressurized gas or liquid in the valve from escaping to the atmosphere.
-
REV 1: Valves (MD-023) Page 12 of 42
5. TYPES OF VALVES AND THEIR FUNCTIONS
We will discuss types of valves that are either manually or automatically
operated. They are:
Butterfly Valve
Globe Valve
Ball Valve
Gate Valve
Plug
5.1. BUTTERFLY VALVE
The opening element in a butterfly valve is a flat disc. The disc rotates
around a central pivot point and fits against the valve seat when fully closed.
The flat disc fills the entire area of the valve body. The butterfly valve offers
very little resistance to flow when it is fully open.
Figure 3 Butterfly Valve
Open Closed
Disc Disc
-
REV 1: Valves (MD-023) Page 13 of 42
The opening element of a butterfly valve is a flat disc. When the disc is
perpendicular to the pipeline, it stops the flow.
Butterfly valves need only one-quarter of a turn to move from a fully closed to
a fully open position. A handle is often used instead of a hand wheel to turn
the valve stem.
Butterfly valves are used as control valves in low-pressure gas pipelines.
They can be set at any position between fully open and fully closed.
Butterfly valves are also sometimes used in low-pressure liquid pipelines.
Butterfly valves are not used in high-pressure pipelines because they do not
provide complete shutoff.
A butterfly valve and its engineering symbol are shown in figure 4.
Figure 4 Butterfly valve and its Engineering Drawing Symbol
The vertical lines at either end of the symbol mean that the valve has flanges
on the valve body. You may see these lines on any type of valve.
-
REV 1: Valves (MD-023) Page 14 of 42
5.2. GLOBE VALVE
The opening element in a globe valve is a plug shaped disc operated by a
hand wheel. The disc moves away from the valve seat to open the valve.
The disc fits tightly into the seat to close the valve. When closed, the valve
completely shuts off the flow of liquid or gas.
Figure 5 Globe Valve
The opening element is a disc, which moves down to shut off flow. The
element can be positioned to allow different rates of flow.
The main function of the globe valve is to regulate the flow of liquids and
gases. The valve may be placed in any position between fully open and fully
closed.
Globe valves are used mainly as control valves, when the rate, volume, and
pressure of flow must be frequently adjusted.
-
REV 1: Valves (MD-023) Page 15 of 42
Figure 6 Globe Valve and its Engineering Drawing Symbol
Globe valves are primarily used as control valves to regulate fluid flow.
-
REV 1: Valves (MD-023) Page 16 of 42
5.3. BALL VALVE
In a ball valve, the opening element is a ball with a hole through the centre.
When the valve is fully open, gas or liquid flows through the valve easily. The
hole in the ball is the same size as the pipe, so there is no obstruction to flow.
Figure 7 Ball Valve
The ball element rotates within the valve body to open and close the valve.
Large ball valves are operated by hand wheels. Small ball valves have a
handle, connected to the stem that turns the ball.
A one-quarter turn of the valve stem will rotate the ball 90. This is enough to
move the valve from a full open to a full closed position.
Ball valves have the advantage that they can be opened and closed more
quickly. They are used in high-pressure liquid and gas pipelines as quick
shutoff valves.
Ball valves are usually set in a fully open or fully closed position. Because of
their construction, ball valves can be opened slowly without damage to the
ball. For this reason, they can be used as bypass valves. Bypass valves are
opened slowly to allow pressure to build up gradually in a pipeline.
Open Closed
-
REV 1: Valves (MD-023) Page 17 of 42
Figure 8 Ball Valve and its Engineering Drawing
Both ball valves and butterfly valves open and close with a 90 turn.
-
REV 1: Valves (MD-023) Page 18 of 42
5.4. GATE VALVE
The opening element is a gate valve is a wedge shaped disc or grate
attached to the end of a threaded stem. The gate fits into a wedged shaped
seat in the valve body to stop flow through the valve.
Turning the hand wheel raises and lowers the valve gate. When the valve is
fully opened, the gate is positioned above the passage in the valve body.
This allows full flow in either direction, with little or no restriction.
When the gate valve is fully closed, the gate fills the passage and it stops flow
through the valve completely.
Figure 9 (a) Rising Stem Gate Valves
Closed Open
-
REV 1: Valves (MD-023) Page 19 of 42
Figure 9 (b) Non-Rising Stem Gate Valves
The gate element is raised and lowered by the hand wheel. When the valve
is closed, the gate fits tightly against the valve seat, stopping flow completely.
5.4.1. RISING STEM
Large gate valves normally have rising stems. When the hand wheels turned,
the stem rises out of the valve bonnet through the hand wheel. The stem
shows the position of the disc, and shows if the valve is opened or closed. In
small gate valves, the wheel and stem may rise together.
5.4.2. NON RISING STEM
Some gate valves have a nonrising stem. The stem does not come out of the
valve body. The gate moves up on the stem. This type of valve is used
where there is not enough space for the stem to rise out of the valve body.
Most gate valves are manually operated.
Gate valves provide a good seal against flow. For this reason, they are
normally used as isolation valves in high-pressure hydrocarbon pipelines.
Stem
Gate
Inside
Thread
Closed Open
-
REV 1: Valves (MD-023) Page 20 of 42
Gate valves are the most commonly used valves in process operations
plants.
Figure 10 Gate Valve and its Engineering Symbol
Gate valves can stop flow completely even on high-pressure lines. For this
reason, they are the most common valves in process operations.
-
REV 1: Valves (MD-023) Page 21 of 42
5.5. PLUG VALVE - FIGURE 11
This multi-turn valve derives its name from the rotating plug, which forms the
closing element; the plug may be cylindrical or truncated.
In the open position the fluid flows through the hole in the plug.
Lubricated plug valves rely on a sealing compound injected between the plug
and the valve body
Whilst sleeved plug valves are fitted with a soft insert between the plug and
the body.
Figure 11 Plug Valve
Wrench
Sealant Groove
Body
Sealant Fitting
Stem
Gland Flange
Plug
-
REV 1: Valves (MD-023) Page 22 of 42
6. AUTOMATIC VALVES & THEIR FUNCTION
Automatic valves, once installed, operate by themselves. They are not
opened and closed by an operator.
6.1. CHECK VALVES (NON RETURN VALVES N.R.V )
Check valves are used to permit flow in only one direction in a pipeline.
There are two types of check valves:
Swing Check Valves
Ball Check Valves
6.1.1. SWING CHECK VALVES FIGURE 12
In a swing check valve, the opening element is a disc attached to a hinged
arm.
Figure 12 Swing Check Valve
Closed Open
Hinged Disc
-
REV 1: Valves (MD-023) Page 23 of 42
Upstream pressure causes the hinged disc to rise, opening the valve. Higher
downstream pressure will cause the valve to close.
The pressure of liquid or gas flowing through the valve holds the disc open,
allowing full flow. If flow stops, or the pressure downstream of the valve
becomes higher than the pressure upstream, the hinged arm will swing down.
The disc will cover the passage and seal the valve. The higher downstream
pressure will press against the disc to keep it tightly closed. None of the
liquid or gas that has already passed through the valve will be allowed to flow
back through the valve.
Swing check valves can be installed vertically or horizontally. Gravity will
close the valve if flow stops.
6.1.2. BALL CHECK VALVE - FIGURE 13
The opening element in a ball check valve is a ball.
The ball check valve works on the same principle as the swing check valve.
The pressure of liquid or gas in the pipeline opens the valve by raising the ball
from the valve seat. If flow stops or reverses direction, the ball drops back
into the seat. The higher pressure of the liquid or gas downstream holds the
valve closed.
The ball check valve shown in figure 12 must be installed in a horizontal
position. Some ball check valves are made so they can be installed vertically.
That is, flow from below raises the ball to allow liquid or gas to pass through
the valve.
There will usually be an arrow on the outside of the check valve body to
indicate the direction of flow.
-
REV 1: Valves (MD-023) Page 24 of 42
Figure 13 Ball Check Valve (Top is open, bottom is closed)
Higher downstream pressure will cause the element to seat, closing the valve.
-
REV 1: Valves (MD-023) Page 25 of 42
6.2. FUNCTION OF CHECK VALVES FIGURE 14
Check valves are used to control the direction of flow in a pipeline. Swing
and ball check valves can be used in both liquid and gas pipelines. They are
often installed downstream of reciprocating pumps and compressors.
A check valve and its engineering symbol are shown in figure 14.
Figure 14 Check Valve and its Engineering Drawing Symbol
The circle on the symbol indicates the upstream side of the check valve. The
arrow on the valve casing indicates the direction of flow for installation.
-
REV 1: Valves (MD-023) Page 26 of 42
6.3. NEEDLE VALVES - FIGURE 15
Needle valves are a form of the globe valve and are intended for low flow, fine
adjustment conditions (see Figure 15).
Figure 15 Needle Valve and its Engineering Symbol
The spindle ends in a tapered needle, which moves into the valve seat to
restrict or shut off the flow of fluid through it. A hand wheel operating the
spindle controls the 'in and out' motion of the needle to and from the valve
seat.
Advantages
Very precise flow control at low rates.
-
REV 1: Valves (MD-023) Page 27 of 42
Disadvantages
Needle valves impose a high restriction to the fluid flow, so
there is a very high pressure-loss,
The small flow passage between the needle and seat restricts
the use of this valve to low flow rates.
The seat and needle are prone to damage if the fluid being
handled contains suspended solids.
6.4. SAFETY RELIEF VALVE
Safety relief valves prevent excess pressure, which may cause serious
accidents.
The opening element in the safety relief valve shown in figure 16 is a disc
held closed by a spring. The amount of tension on the spring is adjustable.
Maintenance personnel set the tension on the spring when the valve is
installed.
The safety relief valve pressure setting is always higher than the normal
operating pressure of the system it is protecting. It is always lower than the
pressure, which could damage the system.
-
REV 1: Valves (MD-023) Page 28 of 42
Figure 16 Safety Relief Valve
Safety relief valves prevent damage to equipment from overpressure. When
fluid pressure at the inlet exceeds the spring tension, the valve disc will rise,
opening the valve.
Spring
Base
Inlet
Disc
Outlet
Adjusting
Screw
-
REV 1: Valves (MD-023) Page 29 of 42
For example, a safety relief valve is often used to protect a positive
displacement pump or compressor. If the normal discharge pressure is
150psi, the safety relief valve might be set at 180psi. If the pressure in the
discharge pipeline goes up to 180psi, the pressure will overcome the tension
of the valve spring. The valve disc will lift up off its seat. The liquid or gas
causing the high pressure will then escape through the valve as shown in
figure 16.
Figure 17 Safety Relief Valve Operation
The valve opens when the fluid pressure at the inlet is higher than the setting
on the relief valve.
Once the pressure in the pipeline falls below 180psi, the spring will force the
valve disc back down in its seat.
Safety relief valves are used in both liquid and gas pipelines. These valves
are also installed on process vessels and tanks to protect them from excess
pressure build-up.
Some safety relief valves will allow the liquid or gas to escape to the
atmosphere. Hydrocarbon liquids and gasses that escape through safety
relief valves are piped to a burn pit or flare.
Inlet
Valve Fully Open
Inlet
Valve Partially Open
Inlet
Valve Closed
-
REV 1: Valves (MD-023) Page 30 of 42
Figure 18 Relief Valve and its Engineering Drawing Symbol
Flow through the relief valve will only occur under high-pressure conditions.
-
REV 1: Valves (MD-023) Page 31 of 42
7. THE OPERATION VALVES
In this part of the module, you will learn how valves are operated.
Valves can be operated manually or automatically.
Valves can be operated locally or by remote control.
7.1. MANUAL OPERATION
Manual operation occurs when an operator opens, closes, or adjusts a valve.
Figure 19 shows one method of manual operation. The operator turns a hand
wheel or moves a handle that changes the position of the valve disc or ball.
Figure 19 Manual Operation
The operator turns the hand wheel clockwise to close the valve. He opens
the valve by turning the hand wheel counter clockwise.
-
REV 1: Valves (MD-023) Page 32 of 42
7.1.1. HANDWHEEL OPERATION
In process operations, all valves with hand wheels operate the same way; you
turn the hand wheel in a counter clockwise direction to open the valve and in
a clockwise direction to close the valve. Generally the hand wheels have
arrows marked on the surface to show the direction for opening and closing
the valve.
There are three important points to remember for hand wheel operation of
gate valves:
Grease the stem after operation.
This helps to lubricate the stem, prevent corrosion, and keep
sand out of the threads. In some plants you will put a plastic
hose over the threads after greasing them.
Always turn the hand wheel turn closed after fully opening
the valve.
This prevents the valve from seizing or sticking in the open
position.
Always turn the hand wheel turn open after fully closing the
valve.
This prevents the valve from seizing or sticking in the closed
position.
7.1.2. HANDLE OPERATION
In general, to open a handle-operated valve you put the handle in line with the
pipe work. To close the valve you turn the handle 90 to the pipe work. The
movement from open to close is 90.
-
REV 1: Valves (MD-023) Page 33 of 42
7.2. LOCAL OPERATION
Figure 20 shows local operation of a motor-operated valve (MOV).
Local operation occurs close to the valve. If the valve is operated by a
motor, the controls for the motor are located near the valve.
Figure 20 Local Operation of an MOV
The local controls are located close to the valve, in the field.
The operator in figure 20 is pressing a button that operates an electric motor.
The electric motor does the work of opening or closing the valve. This is
local operation of the valve.
-
REV 1: Valves (MD-023) Page 34 of 42
7.3. REMOTE OPERATION
Remote means at a distance, or away from. Remote valve operation is
usually performed by control room personnel. A remotely operated valve is
equipped with a valve actuator. This is a mechanical device that provides
force to open, close, or adjust a valve.
Valve actuators may be operated electrically, pneumatically, or hydraulically.
In figure 20, the operator is using an electrically operated actuator to operate
a valve.
In figure 21, electric wires connect the valve actuator mechanism to a
pushbutton switch in the control room. A valve position indicator will be
located near the pushbutton switch that operates the valve. The indicator
shows whether the valve is open or closed. A control room operator can
operate the valve by pressing the pushbutton switch while he watches the
position indicator.
Figure 21 Remote Operation
Remote valve operation is normally performed in the plant control room.
-
REV 1: Valves (MD-023) Page 35 of 42
7.4. AUTOMATIC OPERATION
Automatic operation of a valve is when an instrument control system is used
to open, close, or adjust a valve. Figure 22 compares automatic control with
manual control.
Figure 22 Controlling Water Level
Set Point Pointer
Level Indicator
Float
Automatic
Control Valve
Sensor
Water Level
Outlet Line
Manually
Operated Valve
Inlet Line
100%
Transmitter
50%
Controller
0%
Desired Water
Level
Inlet Actual Water
Level
-
REV 1: Valves (MD-023) Page 36 of 42
Figure 22 shows an example of automatic control. The valve position
changes automatically to adjust the water level in the tank.
The objective in each system is to control the water level. The system on the
right is a manual system. An operator opens and closes the valve in the inlet
line as necessary to keep the water level at the set point. In this case, the
set point is 50%. The operator observes the level indicator and adds water
when the level drops below 50%.
The system in figure 22 is an automatic system. A sensing instrument
continuously monitors the water level in the tank. Another instrument, called
a transmitter, sends an electronic or pneumatic signal corresponding to the
water level from the sensor to a controller. A controller is an instrument that
takes the place of the operator in adjusting the valve.
The controller is preset to a specific set point. The controller compares its set
point with the information it receives from the transmitter about the actual
water level. If the water level is not exactly at the set point, the controller
automatically adjusts the control value to bring the level back to the set point.
7.5. LOCAL AUTOMATIC OPERATION
Local automatic operation means that a process instrument control system is
located near the process control valve. A plant operator sets the instrument
controller to a required set point. The automatic controller operates the valve
as necessary to control the process.
7.6. REMOTE AUTOMATIC OPERATION
In remote automatic operation, the controller that operates the valve is
located in a control room. The control room may be quite far from the valve.
A control room operator sets a required set point on the controller. The
controller opens and closes the valve to maintain the process at set point.
-
REV 1: Valves (MD-023) Page 37 of 42
8. VALVE ACTUATORS
A valve actuator is a device that provides the force to open, close, or adjust a
valve.
8.1. ELECTRIC MOTORS
Some valves use an electric motor as an actuator. These valves are called
motor-operated valves, or MOVs.
The motor-operated valve has two main parts: the valve itself and a motor
driven screw stem. The motor uses two bevelled gears to move the stem up
and down.
Figure 23 Motor Operated Valve
A motor drives a bevelled gear, which in turns a gear on the stem. The
rotation of the gears lowers or raises the stem.
The drive is attached to the shaft of the motor through speed reducing gears.
The stem gear is threaded in the centre. The valve stem screwed through
the gear.
Closed
Speed
Reducing Gears
Bevelled Drive
Gear
Valve
Threaded
Stem
Actuator
Bevelled
Stem Gear
Motor
Valve Gate
Motor
-
REV 1: Valves (MD-023) Page 38 of 42
As the motor turns the stem gear, the valve stem threads itself inside the
stem gear. This threading action moves the stem up or down, depending on
the direction of the motor rotation.
A motor operated valve is also equipped with a hand wheel. The hand wheel
allows the valve to be manually operated if the actuator fails.
8.2. PNEUMATIC ACTUATORS
A pneumatic actuator operates by air pressure. A pneumatic valve actuator is
attached to the valve. The valve stem connects the valve disc to a
diaphragm inside the actuator.
Figure 24 Pneumatically Actuated Control Valve
Most controlled valves use pneumatic actuators. Air pressure from the
actuator positions the valve stem.
In figure 25 (a), air pressure from below the diaphragm pushes the diaphragm
pushes the diaphragm up to open a valve.
In figure 25 (b), air pressure from above the diaphragm pushes the diaphragm
down to open a valve.
Stem moves up
Stem moves down
A B
Air Supply
Air pushes down on Diaphragm
Air Supply
Diaphragm
Air pushes up on Diaphragm
-
REV 1: Valves (MD-023) Page 39 of 42
A strong spring inside each valve will fully open or fully close the valve if the
air supply fails.
8.3. HYDRAULIC ACTUATORS
A hydraulic actuator uses the force of a pressurized liquid; usually oil, to
position the valve stem.
In a hydraulic valve actuator a cylinder assembly is attached to a valve. A
piston inside the cylinder moves up and down. The piston is attached to the
valve stem.
When hydraulic oil is pumped to the topside of the piston the valve will close.
When hydraulic oil is pumped to the bottom side of the piston, the valve will
open.
Figure 25 Hydraulically Actuated Control Valve
The pressure of hydraulic fluid in the actuator causes the valve stem to rise or
fall.
Outlet Port
Seat
Inlet Port
Body
Disc Bonnet
Valve Stem
Actuator Stem Actuator
Piston
Cylinder
Valve Disc
Down
Up
-
REV 1: Valves (MD-023) Page 40 of 42
8.4. SOLENOID / MAGNETIC ACTUATORS
Solenoid operated valves are not very large. They are commonly used to
shut of the instrument air supply to control valves. They are used most often
for emergency shutdown systems (ESDs). Figure 26 shows a photograph of
a solenoid valve.
Solenoid valves use the principle electromagnetism to operate. As long as
the coil is energized, electromagnetism holds the core down. The valve
remains open, and instrument air reaches the control valve. When the coil is
deenergized, as the result of an emergency, for example, the solenoid shuts
off the instrument air to the control valve. Depending on how it is set up, the
control valve will open, close, or remain in its position.
Figure 26 Solenoid Valve
-
REV 1: Valves (MD-023) Page 41 of 42
Figure 27 Solenoid Valve Operation
Electromagnetic force from the coil holds the solenoid core down, allowing
flow of instrument air to the coil is cut off, the solenoid core moves up, cutting
off the instrument air supply to the actuator.
Spring
Expands
Instrument
air
Spring
Compressed
To exhaust
Coil denergized
valve moves
up to close
Instrument air to
actuator
Coil energized valve moves down to open
-
REV 1: Valves (MD-023) Page 42 of 42
9. GLOSSARY
Check: To stop; to hold back
Pneumatic: Moved or worked by air pressure
Regulate: To fix or adjust the time, amount, degree, or rate
Remote Control: Controlling indirectly or from a distance
Vent: An opening for the escape of a liquid or gas for the relief of pressure
Gland: The movable part used in a stuffing box to compress the packing
Hydraulic: Operated or moved by means of a liquid
Pivot: A shaft or pin on which something turns
Set Point: A setting on a controller that you want a process variable to be
Valve Actuator: A mechanical device that provides the force open, close or adjust a valve