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GENERAL DESCRIPTIONS OF
VALVES
Basic Introduction to Valve Types
Air/Vacuum Relief Valve – To release pressure or vacuum
when filling or emptying a tank or pipeline, automatic
operation.
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Ball Valve
Spherical ball between two seats, with hole
bored through, acts as the closing member.
Operated by a quarter turn. May be full or
reduced bore and body construction may be in
one, two or three pieces. Top entry valves are
assembled through the top, side entry valves
through the side of the valve. Floating ball
valves for small sizes, trunion mounted valves
with a bottom bearing for large sizes. Valves
can be multiport, eg 3-way, Ball Valves have the
advantages of positive tight shut off, low
operating torque and low resistance to flow.
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Butterfly Valve
An economical valve with a quarter turn, low
torque operation. Uses a rotating disc as
closing element. Either concentric or eccentric
disc and seating arrangement. Flanged or wafer
design, soft or metal seats.
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Check Valve
Self-acting valve allowing flow in one direction
only.
Swing check has a hinged disc as closing element.
Dual plate check, operates with two hinged discs.
Lift check, operates with a piston or ball as
closing element, to provide some damping.
Wafer check for fitting between flanges. |
Control Valve
For
regulation of fluid flow. Automatic control by response
to process signal, or self acting through up-stream and
down-stream pressure differential. Valves are used with
appropriate actuation.
Diaphragm Valve
Flexible elastomeric diaphragm with a piston operated by
a multi-turn handle. Can be weir type or full bore. The
diaphragm isolates the valve working parts from the
operating fluid.
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Float Valve
Automatic control and maintenance of fluid levels in tanks and
vessels.
Gate Valve
Disc with two seats as the closing element,
raised and lowered with a stem. Wedge gates are
tapered and may be solid, flexible or double
disc type; body seats are renewable. Parallel
have two discs separated by an expanding spring.
Through conduit gate valves use a parallel disc,
extended with a circular port to obtain a smooth
bore in the open position. Knife gate valves use
a narrow section parallel disc tapered at the
end to provide a simple cutting edge. |
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Globe Valve
Closure by means of a disc as shown in the
diagram. Seats can be integral or renewable.
Valves may be straight, angle or oblique (Y),
also three port changeover valves with two
separate seats. Parabolic or needle shape disc
for throttling service. |
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Line Blind Valve
Pipeline shut-off arrangement using spectacle
blinds between two flanges which are turned
around for opening or closing.
Piston Valve
The disc is replaced with a piston arrangement
and a lentern bush, elastomer upper and lower
valve rings. |
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Plug Valve
Conical plug as the closing element, with a
quarter turn operation. A sealing compound
(lubricants) is usually injected between the
plug and valve body. Multi ports in various flow
configurations. Sleeved Plug Valves have a soft
insert between the plug and valve body.
Pressure Reducing Valve
Automatic valve for reduction and maintenance of
upstream line pressure irrespective of pressure
changes or flow variation. Can be pilot
operated.
Safety and Safety Relief Valve
A spring loaded valve which discharges fluid
automatically, to prevent a predetermined safe
pressure being exceeded.
Solenoid Valve
A valve usually of the needle type where the
closing member moves under the action of a
solenoid.
Thermal Relief Valve
Operates as a safety valve to prevent a
pre-determined pressure being exceeded due to
thermal expansion of contained fluid.
Visor Valve
A valve combining the characteristics of ball
and butterfly valves, where the closing member
is shaped to conform to the walls of the valve
body giving full bore flow in the open position. |
Design
Options and Manoeuvre
Anti-Static
Valve
with non-metallic (soft) seating in certain
circumstances require anti-static devices to ensure
electrical continuity between all parts of the valve.
Bellow Seal Valve
A
valve designed for zero leakage service. The stem is
weld-sealed to the body with a flexible bellows to
obtain nil leakage to the atmosphere.
Bypasses
Used
for equalizing the pressure around the disc of the main
valve before opening. The bypass valve can form an
integral part of the main valve or can be attached by
piping.
Cryogenic Valve
Designed to operate at low temperatures, often down to –
196oC. A part from material selection
criteria, design features include extended bonnets and
stems to isolate the valve from the actuator mechanism.
Emergency Shut Down Valve
These
valves are automatic and operate “fail safe”.
First Safe Valves
Ball
valves which have a secondary metal to metal seal for
use when the non-metallic seal is destroyed by fire.
Manufacturers can qualify a specific design by testing
to certain standards eg BS 6755pt2.
Valve Manoeuvre
Valves can be operated manually with hand or chain
wheel, with gear assistance or by using actuators.
Lock open and lock closed features can be designed in or
added as a separate device.
Actuators
Mechanical valve manoeuvre using electric motors or
hydraulics/pneumatics. A wide range of actuators
are available for different output torques and thrusts.
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