Pressure Surges from gas cylinders

[DrP]

I am glad my equipment has a safety pressure valve on it....  :-/  I have 2 Nitrogen cylinders feeding a TGA machine and other cylinders feeding other machines with Oxygen. The O2 line has always been fine. The pressure regulator on it is quite expensive. The pressure regulators on the N2 cylinders seem to allow high pressured gas surges through the line. I have set the regulator to about 40 psi but regularly get surges up to several hundred psi.  This doesn't happen very often and at first I put it down to a dodgy pressure regulator. One is old. The other regulator is brand new.  Even the brand new one now though seems to give a surge sometimes, especially when I first turn on the gas...  the pressure surges high then drops back to what I had it dialled into. With the older pressure gauge...  albeit rarely, I still get the odd surge of high pressure from time to time (once or twice a week) where it just blows through the blow out valve for a few seconds before returning to the set psi. This happens halfway through the day sometimes without even touching the regulator.  

Are these surges normal? I assumed a faulty pressure regulator but I still get surges from time to time when opening the bottle with the brand new regulator. The older regulator IS a little sticky, but the brand new one surely shouldn't allow 2-300psi pressure surges when it is set to 30psi max. Are my old sticky regulator AND my brand new one both faulty?

I guess it isn't THAT much of a problem because there is an over pressure release safety valve before the line enters the kit, but I still do not like it going over the pressure I have set on the dial.

 

Thanks.

 

 

 

 

[Bender]

I have never encounteted that behaviour in pressure regulators. I can see how there could be a (small) surge when the pressure is switched on, but a surge suddenly happening is odd.

Are these electronic regulators?

Are there large fluctuations in the flow? 

[John Cuthber]

Surges when you first turn the supply on are common- it takes a finite time for the bits of metal to move and throttle the supply.

In principle, you should always turn the regulator "off" before connecting the supply (I'm not sure anyone actually does this unless it's critical).

Surges during the day for no reason seem to me to be  saying it's time to replace the regulator.

Adding some sort of buffer volume may reduce  the magnitude of the surge, especially if it is preceded by a flow restriction of some sort.

[DrP]

Thank you for the replies - The surge isn't that bad - I do think I will need to replace one of the regulators at some point though   -  the dial sticks, so when you dial up the pressure it is nothing, nothing, nothing, then suddenly a surge of several hundred psi. The pressure can be dialled down again. I have worked around it for now, but will need to replace it at some point.

 

Thanks again for your replies.