Spring-loaded check valves are sold by cracking pressure, from a fraction of a psi up to tens of psi, and the valve stays shut until the differential beats the spring. For relief valves, cracking pressure is the point of first measurable flow, usually at or slightly below the stamped set pressure, and it is checked on the test bench during recertification.
Check valve on the instrument line has a 10 psi cracking pressure, that's why the gauge reads low downstream.
Also heard as
- crack pressure
- opening pressure
Related terms
Check valve
A self-acting valve that lets fluid pass in one direction and closes on its own when flow tries to reverse.
Relief valve
A spring-loaded valve for liquid service that opens gradually as pressure rises past its set point.
Crack
To open a valve just slightly, letting a small, controlled flow through.
Safety valve
A spring-loaded pressure relief valve for steam, gas or vapor that opens with a rapid full lift at set pressure.