I've seen it time and again where operator sees pressure a bit low, operator turns regulator up and doesn't see pressure increase, so operator keeps cranking it up until it's maxed, then leaves it like that. The problem was never the regulator, it was something wrong like a washed out tip, bad check valve, bad pump seals or o-rings, so the pump just can't achieve desired pressure. Then the trigger is released, suddenly the flow needed to the bay drops and the regulator being maxed out kicks in and pegs the gauge. You shouldn't have to set the pressure with the trigger released, but for f***'s sake if the pressure doesn't go up, stop turning it. I always set pressure with the trigger pulled, but if I'm trying to get 1200 PSI and it doesn't make it, I turn it back down until I see the needle drop a bit.