Need Help w/ O2 Regulator & Metering Valve

[gxsr_sarge]

Greetings,

After PP blending EAN and Trimix for the last few months and learning the "old school" method, I've finally decided to incorporate a mixing stick. For now, I just plan to mix/bank EAN32. I have a Bauer Oceanus 5 cfm and am good w/ the Oxyhacker stick model (will build as is - cudos for the book!) and probably an Oxycheq "El Cheapo" analyzer (I think I'll have fun building it).

The problem that I'm having is trying to identify an O2 regulator/metering valve to come off of the "T" of O2. I've called GMC and they don't have any (or otherwise wouldn't recommend anything for fear of getting sued) and I've drunk-dialed a few medical supply outfits and/or checked some web sites and they only seem to have the small regulators for the portable tanks (NOT the T cylinders).

From what I've gathered, I'm thinking I need a rig that includes a CGA 540 connection to a HP gauge (to read the tank pressure) that's steps down the pressure (50 psi?) to another LP gauge that's attached to a flowmeter where I can control the O2 output in liters/minute. At the bottom of the flowmeter, I connect a hose to a barb which connects to the stick input.

What am I missing and where can I find this?????

 

[Camerone]

You've hit it... and Flea-Bay is the answer to your question. What you need is a welding regulator for oxygen, and they're very cheap. They're usually single stage units that have a large handle on the front for adjusting output. They're not demand regulators like a scuba reg, but just something to step down the pressure. Do an eBay search for "oxygen regulator" and you should have no problem finding what you want.

If I were you, I'd pick up two - one for helium as well. Helium is a different fitting, but Northeast Scuba Supply has a great adapter that will convert from a CGA 540 oxygen fitting to an inert gas fitting (CGA580). It's here: Oxygen Stuff - Filling Adapters - O2 to Inert Gas Adapter - Northeast Scuba Supply

Why do it that way instead of an inert gas regulator? Two reasons - one is the ability to keep a single parts kit set around to rebuild the regulators... and the other is to be able to swap if something fails when there's not time to fix it. Kind of the whole redundency principle.

FWIW, the O2 reg I have simply reads LPM on the output side, and the output pressure doesn't really matter. Mine does up to 10 LPM; with my 3.5 cfm compressor, that's good for about 35% nitrox.

All that said, I tried it out, but there's no point in continuous blending for me. Nitrox isn't worth the time unless it's 50%, and I can't pump that through an oil lube compressor. Any advantage gained 32% can be easily done with a 19cf bottle of pure O2 tucked under the arm to clean myself up at 20 feet, and it's a lot less hassle than mixing. Trimix is hard to CB into the 13 or 19cf rebreather bottles...much easier to just pp blend them.

 

[gxsr_sarge]

Cameron,

YOU DA' MAN. Thanks for that very helpful response. I've been looking up the Welding Regulators and the "output" gauges seem to be in PSI and not LPM. Does it really doesn't matter as long as I record the right flow for what I need for CB?

 

[gkndivebum]

I've found that with my setup it helps to have a little back pressure on the output side of the welding regulator to help keep it operating closer to an "ideal" pressure. With the small amounts of O2 necessary to blend EANx on a small compressor most welding regulators have a hard time keeping a constant flow at such a low output pressure. I use a flow control orifice from McMaster-Carr for that.

For example, I have a RIX SA-6, which pumps somewhere between 4 and 5 CFM. For 32% EANx, I need an additional 11% O2 over air (21%); I'd like to limit the mix I can make to something around 40% EANx, or an additional 19% over air. McM-C sells precision orifices with 1/4 NPTM inlets and barbed tube outlets (3/16ths is a good size) in a variety of sizes. So, let's get one that yields 20% of 5 CFM at 40 PSI, or about 1 CFM. According to this:

About Flow Control Orifices

I would need an orifice diameter of 0.038" for 1.12 SCFM @ 40 PSI. Close enough. The part number is 6183T61; I removed the outlet fitting on my welding O2 reg and replaced it with this. It works very well - for 32% EANx blending I find that the O2 flow stays very steady at about 22 PSI.

 

[gxsr_sarge]

gkndivebum,

Thanks for your post as well. I now understand the use of the orifice and actually went back and re-read the relevant section in the Oxyhacker's book (and now understood it!). I'll go ahead and get that size orifice as well, perhaps, as a few other sizes just to be sure.

 

[gxsr_sarge]

Success!! It works perfectly. Nice work Oxyhacker.

I had to end up "making" the flow restrictor off of the welding O2 regulator by removing the stock one (1/4" MNPT) and inserting an adapted Home Depot 1/4" MNPT/ 1/4" barb. I adapted it by inserting a drilled nylon cap on the inside. I drilled a 1/32" (.03125") hole. At a 32PSI flow I get 30% O2 on the pre-compression mix. I had to make it b/c McM-C was on a 2 week back order on the part that gkndivebum referred to above. gkndivebym, you were spot on with the math!

At first, I was getting about more 3% 02 on the post-compression blend than in the pre-compression blend. I also had to crank the O2 up to about 40PSI to get it to 30% on the pre-compression mix (as opposed to now, where I just use about 32PSI to get to 30% O2. I realized that the sensor was not getting enough flow - it was too far removed from the flow. So I modified it so that the sensor's "X" was in the path of the flow. Now I only have a difference of .5% between pre and post compression mixes - .5% less on the post. I'll live with that.

I also had a hard time finding a 1" flexible hose. I finally found a washing machine hose (for water) that was 1" ID and was made of flex tubing. Works like a charm.

Building the El Cheapo was fun as well.

My next project is introducing Helium and making pre-blending trimix.

Thanks again

 

[Fl_Key_Guy]

For the next builder's info:
I used 1" bilge pump hose for my stick to compressor connection- the extremely flexible lightweight thin plastic corrugated style. You can buy by the foot from a roll. I suspect that is probably similar to what you bought rather than the heavy rubber style washer hose. There is no odor generated by this hose either, unlike some others I considered. My downfall was thinking I didn't need hose clamps as it fit snugly at first.

I used an adjustable medical oxygen regulator (with a CGA540 connector) that included a Bernoulli flow meter reading in lpm. No orifice was needed- the pressure is preset and a needle valve controls flow.

 

[gxsr_sarge]

Just one point of clarification: The 1" tube I got from Home Depot was the flexible corrigated type - not the rubber hose.

Thanks