A valve is a mechanical device that controls the flow of fluid and pressure within a system or process. A valve controls system or process fluid flow and pressure by performing any of the following functions:
# Stopping and starting fluid flow# Varying (throttling) the amount of fluid flow
# Controlling the direction of fluid flow
# Regulating downstream system or process pressure
# Relieving component or piping over pressure
There are many valve designs and types that satisfy one or more of the functions identified above. A multitude of valve types and designs safely accommodate a wide variety of industrial applications.
Regardless of type, all valves have the following basic parts: the body, bonnet, trim (internal elements), actuator, and packing. The basic parts of a valve are illustrated in Figure bellow.
