Instrumentation and Control

"A double acting actuator is a mechanical device designed to supply powered bi-directional actuation for secondary mechanisms. This is in contrast to single action or spring return actuators and solenoids, which feature a powered stroke in one direction only and rely on a secondary source of energy to reset or return the actuator. The double acting actuator is typically driven by electric motors or compressed oil and gas. Electrically-driven double action actuators supply their bi-directional force by means of a motor reversing control circuit. Compressed gas and oil actuators feature opposed inlet valves that direct the motive agent to one side or the other of the actuator mechanism."

For continued reading:
http://www.wisegeek.com/what-is-a-double-acting-actuator.htm
 
If it's pneumatic or hydraulic then the advantages over spring return actuator is that even if the pneumatic or hydraulic pressure gets cut-off the shut-off valve will remain in its last position. Double acting actuators will only work when there is a pressure acting on either one of its 'pressure' port. If there is no pressure also on either of its 'pressure' ports the valve will maintain its last position. You can also work on line like changing the actuator while the valve will maintain its last position state. Whereas in spring return actuators if the supply pressure gets cut-off then the valve will go to it's fail safe position under the action of spring force.

But are you sure that for esd systems double acting actuators are used??? Personally I would never want to use or have seen double acting actuators for critical process systems. Because if the supply pressure gets cut off the valve should always return to its fail safe position which can be both open or close depending on the design of the process. So the reason for the supply pressure getting cut-off should be diagnosed rather than keeping the valve in its last position state.
 
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