Valves isolate, switch, and control fluid flow in piping systems.
Can be operated manually (using levers or gear operators) or remotely (using electric, pneumatic, electro-pneumatic, and electro-hydraulic powered actuators).
Manual valves are usually used only if they will be operated infrequently or no power source is available.
Basic Valve Types
Isolation valves: on/off valves
Typically operated as fully open or fully closed
Designed to have a tight reliable seal during shut-off and minimal flow restriction when open
Switching valves: converge or divert flow in a piping system
Control valves: used to modulate flow (i.e., vary flow by opening or closing by a certain percentage)