For selection of ESD valve actuator supply, what are factors that decide whether ESD valve shall be hydraulic or pneumatic? What are advantages of Hydraulic valves? Both fluids are utilized, and also with a third variant 'gas over oil' combined to give an assured oil pressure.Different solutions are used, depending on a number of factors. One important factor is of course the cheapest commercial solution available ('common practice for size, process fluid (not actuator fluid), pressure class, valve type, size, speed of closure, and branch/application)No firm rules can in my mind be set down, but you will find firm opinions if you start with an exact application and process type.Some general tendencies (not firm rules) can be put down:Smaller valves, air used elswhere -> airLarger valves, hydraulic used elsewhere -> hydraulicFaster movement -> air or fallweight closed hydraulic cylinders if larger valvetypes.Slower or controlled movement -> trotteled air or better controlled (perhaps) hydraulic.Valves on hydraulic operated machines -> hydraulicSubmerged -> hydraulicValves remote from electricity or sources for common air or oil hydraulics -> electric, battery backed, or handpumped hydraulics or battery backed electric. More seldom air.An advantage of a hydraulic systems would be the use 3000 psig fluid as the driving medium. This reduces the actuator size compared to 80 psig air.Pneumatic actuators normally use air. Remote natural gas facilities can use the gas pressure as the driving force. Thus 1000 psig natural gas could reduce the actuator size too.

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