A valve is a mechanical device that controls the flow of fluid and pressure within a system or process. A valve controls system functions:

  • Stopping and starting fluid flow
  • Varying or throttling the amount of fluid flow
  • Controlling the direction of fluid flow
  • Regulating downstream system or process pressure
  • Relieving component or piping over pressure

Although all valves have the same basic components and function to control flow in some fashion, the method of controlling the flow can vary dramatically. In general, there are four methods of controlling flow through a valve.

  • Move a disc, or plug into or against an orifice (for example, globe or needle type valve).
  • Slide a flat, cylindrical, or spherical surface across an orifice (for example, gate and plug valves).
  • Rotate a disc or ellipse about a shaft extending across the diameter of an orifice (for example, a butterfly or ball valve).
  • Move a flexible material into the flow passage (for example, diaphragm and pinch valves).

Categories of Valves

Application Description

Flow regulating valves

For controlling rate of flow.

Temperature regulating valves

For controlling fluid temperature in a system.

Automatic process control valves

For controlling rate of flow relative to value.

Anti vacuum valves

An automatic type of air valve preventing the formation of vacuum in tanks or pipelines.

Blow down valves

A valve which is used for cleaning sludge from a boiler.

Bulkhead valves

A gate valve.

Free ball valves

A valve in which a ball is free to rotate in any direction.

Fusible link or fire valves

A fire prevention valve which has a weighted lever hold open by a wire and fusible link which melts at an increase of room temperature.

Hydraulic valves

A control valve for water, oil, or hydraulic systems.

Jet dispersal valve

A valve incorporating an element by virtue of which the energy within the emitting jet is dissipated.


A single faced type of valve consisting of an open frame and a door and used in terminal positions only. Normal located in tanks or channels for controlling flow in to a pipe.

Plate valves

A gate valve incorporating a sluicing effect.

Radiator valves

A valve controlling the flow of water through a radiator.

Rotary slide valve

A valve in which a rotation of internal parts regulates flow by opening ar closing a series of segmental ports.

Rotary valve

A spherical plug valve in which the plug, which rotates through 90o.

Solenoid valve

A valve operated by by an electrical solenoid.

Spectacle eye valve

A parallel slide valve.

Thermostatic mixing valve

A valve which combines temperature.

Throttle valve

A non tight closing butterfly valve.