Valve actuators are of various types namely electrically operated , pneumatically operated.
Pneumatically operated actuators can be diaphragm operated for globe , gate valves.
Pneumatic actuators can be quarter turn type for ball or butterfly valves.
Pneumatic actuators can be cylinder operated for say Knife gate valves.
Actuators are again single acting spring return type or double acting.
Again actuators can be classified as on-off type or control ( modulating type).
On- off pneumatic actuators can be operated with solenoid valves . As you mention the fluid to be natural gas, you have to select solenoid valves which are intrisically safe at the same time these valves may be placed at a safe distance from the valves and piping. These valves are again actuated by controllers( on -off , PID) connected to the level switches, pressure sensors or temp sensors as the case may be.

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