Pneumatically operated valves are comprised of two basic units:
Controlled air for the actuator is totally isolated from the main input line by a valve with a unique seal arrangement, so that any pressure within its overall range will allow the valve to operate. This permits a degree of pressure fluctuation in the main input line. Two forms of pneumatically operated valves are generally used. Direct acting valves have a drive operator stem, moved by a piston or diaphragm which directly closes or opens the valve orifice, while systems with internal pilot valves use the input line pressure for operating a secondary work valve.
Two styles of pneumatically operated valves are commonly available:
Valves also come in different operating types: