Trends in pneumatic spring return valve actuator selection
Actuator sixing depends on the various valve torque values, minimum supply pressure and actuator-valve safety margins / factors considered to cover the service life of a valve.
When sizing pneumatic actuators for fail-safe valves, torque safety factors can vary depending on project specifications. Valve torques can also vary from break to open and running end to close positions.
End users normally determine the valve safety factor during the design stage and valve manufacturers therefore, do not need to add extra contingencies. Generally, these safety margins are determined with the goal that the valve should operate smoothly throughout its service life, irrespective of the process condition.
Increasingly, the safety factor applied when coupled with the specified minimum sizing and normal supply pressure range for actuation selection, can result in selected actuator torques exceeding the maximum acceptable...