Pneumatically Operated Valves
Pneumatically operated valves are comprised of two basic units:
- an actuator with a piston assembly or diaphragm which develops applied force when pressurized;
- a valve with an orifice to stop or permit air flow via an air pressure plug or disc.
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What Are Pneumatically Operated Valves?
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:
- a hung type piston or diaphragm, which is held open mechanically;
- a floating piston or diaphragm which requires a minimum drop in pressure to hold it open.
Valves also come in different operating types:
- 2-Way Valves (either Normally Closed or Normally Open), often used in safety applications;
- 3-Way Valves (NC, NO and universal), normally used for spring-return and single drive cylinders;
- 4-Way Valves using two 3-way functions at the same time. This type have one NC and one NO, two alternating pressurised and exhausted outlet ports, and are used to control two-directional air motors and double drive cylinders.