What is the main functional difference between a pneumatic diaphragm actuator & a pneumatic piston actuator while operatin a globe valve.Will it be difficult to attain the precise control with piston actuator?For a regulating valve the answer is somwhat more complicated, depending on the position-feedback system from the valve, the total construction diphragm to globe and piston to globe.For a diaphragm operated regulating valve the diaphragm could be larger (in area) than the piston in piston operated valve, and the globe more or less directly attached to the diphragm. Both indicating a more direct connection between pneumatic pressure and position.For a piston operated valve with seal friction for stem and piston seals you would have to depend on a mechanical position feedback. These will cost a lot, give an additional and often unprecise element (depending om price, make and construction) and as a rule need a constant amount of air to function.You would have to check directly for actual valves to give an answer.

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