Which of the following formulas is used to calculate the pressure used to open a POC valve when no pressure is supplied to the cylinder?

• A. PP= (LP/PR) + Z
• B. PP= (PR/LP) + Z
• C. PP= (Z/LP) + PR
• D. PP= [ (LP/PR) + Z ] / [ 1 - (CR/PR) ]

Answer: (A)

Opening a pilot-operated valve depends on translating the actual load pressure into the pilot line through the valve’s pressure ratio and then overcoming inherent friction and seal losses. The load pressure in the line (LP) is effectively reduced by the pilot ratio (PR) to determine how much pressure must appear on the pilot side. You also need a small fixed offset (Z) to account for friction and seating losses. So the pressure that must be applied to the pilot to crack the valve when no cylinder pressure is present is PP = (LP/PR) + Z.

If you tried the other forms, you’d either invert the ratio, mix terms incorrectly, or introduce a nonlinear relationship that doesn’t match how a pilot-operated check valve reacts in practice.