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Modulating control valves each with 4-20mA I to P converter linked to pneumatic a valve positioner controlling a diaphragm actuator. An air-operated valve, also known as a pneumatic valve, is a type of power-operated pipe valve that uses air pressure to perform a function similar to a solenoid.
Control valves are normally fitted with actuators and positioners. Pneumatically-actuated globe valves and diaphragm valves are widely used for control purposes in many industries, although quarter-turn types such as (modified) ball and butterfly valves are also used. Control valves can also work with hydraulic actuators (also known as ...
A pneumatic actuator mainly consists of a piston or a diaphragm which develops the motive power. It keeps the air in the upper portion of the cylinder, allowing air pressure to force the diaphragm or piston to move the valve stem or rotate the valve control element. Valves require little pressure to operate and usually double or triple the ...
Piston actuators use a piston which moves along the length of a cylinder. The piston rod conveys the force on the piston to the valve stem. Piston actuators allow higher pressures, longer travel ranges, and higher thrust forces than diaphragm actuators. A spring is used to provide defined behavior in the case of loss of power.
Pneumatic valve: Actuated using a compressible medium like air, hydrocarbon, or nitrogen, with a spring diaphragm, piston cylinder or piston-spring type actuator; Hydraulic valve: Actuated by a non-compressible medium such as water or oil; Electric valve: Actuated by an electric motor; A wide variety of valve types and control operation exist.
The most common diaphragm valves use pneumatic actuators; in this type of valve, air pressure is applied through a pilot valve into the actuator which in turn raises the diaphragm and opens the valve. This type of valve is one of the more common valves used in operations where valve speed is a necessity.
The measuring element functions to determine when the inlet flow is equal to the outlet flow. The diaphragm itself is often used as a measuring element; it can serve as a combined element. [citation needed] In the pictured single-stage regulator, a force balance is used on the diaphragm to control a poppet valve in order to regulate pressure.
Linear motion can come from either a diaphragm or piston actuator, while rotary motion is supplied by either a vane type air motor, piston air motor, air turbine or gear type motor. Pneumatic motors have existed in many forms over the past two centuries, ranging in size from hand-held motors to engines of up to several hundred horsepower.