Snap action pilot

The graph in Figure 5.37 shows the product loss comparison for a spring valve, a pop/snap action pilot valve and a modulating valve. It is obvious that the product gain of a modulating valve is important (Figure 5.38). 

A more economic solution is to replace the valves with POSRVs with remote pressure sensing. Instead of having a pressure pick-up to the pilot at the inlet of the main valve, pressure can be measured on the system, bypassing the inlet piping and its pressure losses. This solution is also easily field convertible if the snap-action pilot has integral pressure sensing. A typical remote sense point could be a tee into a gauge tap. 

Usually, the pilot valve types which are balanced against backpressure are the modulating pilots (to my knowledge, no snap action pilot currently on the market will accept backpressure... 

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