Oxygen regulator safety

[pescador775]

I can't find the "technical" section in the tech divers area so I'm using this page as default. There are two basic types of regulator, single stage and two stage. Neither is equipped with a safety relief valve. Well, the two stage has a relief ported to the IP side to protect the second stage (got that?) but this does nothing to protect components (think air compressor, booster) in the low pressure air stream. Why bring this up?

The single stage regulators, like the Harris, are really an inexpensive and useful tool for feeding oxygen to a NITROX "stik". However, anything can fail or get out of adjustment. If the first stage poppet valve has a hiccup the flow of oxygen to the stik could go into runaway mode, OUCH. Some solutions involve using an analyzer equipped with an alarm. The input is connected to a solenoid line valve to interrupt flow if levels are too rich. Alternately, what I have done is modify the regulator. Disassemble and drill the low pressure chamber exactly as done by the factory for the LP output, only the new, second port is drilled and tapped 90 deg out from the original port. This is exceedingly easy to do but a drill press should be used and the locations of the holes should be carefully marked to keep everything looking nice. A brass relief valve commonly used in shop compressors is screwed into the new threaded port. However, it may be necessary or convenient to make a small mod to the valve. If your regulator is the 0-60 psi type and the valve is adjustable 0-200, just find a weaker spring for the valve. I did this and adjusted it to 40 psi, the beginning of the danger zone (>40/%) for my setup. Now, should the flow ever become excessive (turn the reg knob to test) the relief valve begins to bleed.

Two stage regs are nice, the cadillac for helium blenders and Haskel rascals. However, it is necessary to install a relief valve set to about 125 psi in line for the Haskal drive air. As above, if used for NITROX stik, a relief should be installed in line. If looks are not an issue simply use a brass "run T" with the correct thread size (usually 1/4 NPT). Same for the single stage if you can't be bothered. Screw the relief valve into one end of the T and the ouput flow restrictor port into the other end.

 

[pescador775]

Hacker was probably the first to raise the issue of excess or runaway oxygen. For example, if the line voltage should drop and the electric motor driven compressor shut down, the O2 level will quickly rise in the stik. If the system comes back up, the compressor intake may be looking at 90% O2. Hence, the book discusses methods for shutting down the O2 flow. My view is that, being in attendance, I will notice the 5HP compressor suddenly going off line and the lights going out. I will also notice the flashing light and alarm horn on my analyser. However, a defective regulator can be more subtle. Sometimes, they go BLOOEY, but more often there is a subtle leak which can cause slow or rapid buildup of flow and subsequent O2 level in the stik. While these regulators are protected by input filters and are apparently reliable, it makes sense to add some sort of "dumb" fail safe and not depend solely on an electronic device to provide warning. Also, since many, if not most, analysers have no alarm, some protection is needed, IMO.

About the Haskel. Actually, I mounted a relief valve on the drive air input, at the booster. I'm not sure if this is the way to go with portable, mini boosters. Depends on the size and vulnerability of the relief valve, I would think. However, if the drive air regulator was lost or damaged, it might be possible to use a SCUBA regulator first stage and I would guess this is common practice. So, that is a vote for a drive air relief valve on the portable booster.

 

[pescador775]

Enclosed is a pic of a single stage Harris medical oxygen regulator retrofitted with a safety relief valve. These were EBay purchases, 5 bucks for the reg and 3 dollars for the valve. I had to buy several to get this price for new, military surplus. The items are really nice, high quality. Thanks, to Oxygen Hacker for stimulating the thought processes leading to the building of a nifty NITROX mixer.

 

[headhunter]

This thread has been moved here from the DIR forum for better visibility and discussion.

Christian
ScubaBoard Advisor