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?
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.

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