The surge of pressure is the "lockUp" pressure which is the difference between flowing pressure "Dynamic Pressure", which depends on how quickly the seat stops letting more gas to flow when the gas solenoid valve in the machine has closed.
When you set a regulator to a certain pressure the seat opens and closes very quickly trying to maintain the actual pressure that the regulator is set at, when the flow is blocked (by the solenoid valve etc.) the seat is supposed to close at the preset pressure but most if not all regulators will allow extra pressure to build up before being able to close off, hence the "surge"
Cheers
When you set a regulator to a certain pressure the seat opens and closes very quickly trying to maintain the actual pressure that the regulator is set at, when the flow is blocked (by the solenoid valve etc.) the seat is supposed to close at the preset pressure but most if not all regulators will allow extra pressure to build up before being able to close off, hence the "surge"
Cheers
