This accidental opening must be recorded as the relief valve test. When the technician actually tests the relief valve after it has already opened, the technician may get an entirely different value. If you exercise these relief valves prior to the actual test, they usually will pass with a reading of 2.0 psi or greater. After the repair, the technician will then test the assembly again. If the same technician were to return a month later and retest this assembly using the U.S.C. procedures, the technician may find that the relief valve is still failing.
Lets try something a little different with the differential gauge.
Open high and low bleed valves on top of gauge. Bleed air from hoses and gauge. Close high bleed valve, close low bleed valve last. Needle on gauge will drop to the point where the relief valve opens. This value should be 2.0 psi or greater.