Valves : General Description 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.
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.

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.
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 byresponse 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.

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.

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.

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.

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.

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.

Safety and Safety Relief Valve
A spring loaded valve which discharges fluid automatically, to prevent a predetermined safe pressure being exceeded.

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.

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

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.

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.

Mechanical valve manoeuvre using electric motors or hydraulics/pneumatics. A wide range of actuators are available for different output torques and thrusts.