"Dave, I can't do that" requested
Can someone who has one of these air compressors check their pressure
relief valve when the tank is at full pressure and tell me if the thing
spring returns or stays out.

Pressure relief valves have hysteresis. They stay open once opened until
the pressure drops to a safe level.

_Occasionally_, if you're operating near the release pressure, vibration
will work a valve open. When it pops, it's going to stay open as long as a
big pump keeps running, because the pressure won't ever drop below the
pop-back-in pressure.

LLoyd