Question O2 flow regulation

[JohnN]

I'm blending nitrox (or trying to) with a nitrox stick feeding a RIX-SA3

My O2 regulator is constant pressure (and old), a constant flow would seem better matched to the job. The only constant flow regulators I can find are for medical O2

Should I just suck it up and get a new constant pressure regulator, or is there something better out there?

 

[tbone1004]

regulator->solenoid->flow meter

keep your current regulator, add the shutoff solenoid so you don't blow anything up, then put a dwyer flow meter or whatever reasonably cheap one you can find on amazon, they're just needle valves so all close enough and that doesn't have to be O2 clean.

I use Dwyers on mine, but you need something like this. 20lpm will get you up to 40% ish on that Rix

https://a.co/d/0OmOeCt

 

[JohnN]

regulator->solenoid->flow meter

keep your current regulator, add the shutoff solenoid so you don't blow anything up, then put a dwyer flow meter or whatever reasonably cheap one you can find on amazon, they're just needle valves so all close enough and that doesn't have to be O2 clean.

I use Dwyers on mine, but you need something like this. 20lpm will get you up to 40% ish on that Rix

https://a.co/d/0OmOeCt

What do you use to trigger the solenoid?

 

[TravisD]

What do you use to trigger the solenoid?

It kind of depends on the compressor, but this is how I set mine up recently (disclaimer - I've tested it but haven't yet done a whole Nitrox banking session yet to see it over time, but I don't have any reason to believe it won't work). Nitrox stick safety shutoff

Basically you want a "normally closed" (NC) solenoid - they're available in various voltages, depending on what you have to work with. I'm using a current operated switch that senses current draw in one of the motor wires after the motor overload contactor. I'm getting 120v from the control transformer, but it's possible that the motor could go off on overload while the controls remain powered up. Sensing the motor current was about the best thing I could figure out to determine actual state other than having some kind of rotation sensor on the pump itself.

The trick to making the O2 regulator happy is to have some sort of flow restriction for it to work against. The flowmeter would give you a number, but at the end of the day you're going to adjust based on what the O2 meter reads coming out of the stick. A needle valve would work, apparently some have had great luck just with a notched screw inserted in one of the tubing connectors to restrict flow. Also, a 2nd regulator stage helps keep things more consistent. My current stick config is Ebay O2 reg > amazon low pressure reg > solenoid > needle valve. Needle valve is rough adjustment, 2nd adjustable reg is where fine tuning happens, main reg gets set to like 60-90psi and stays there.

 

[tbone1004]

What do you use to trigger the solenoid?

There's various ways to do it, but assuming it is electric you just grab a 120v Normally Closed solenoid and tap off of the motor run wires, basically if the motor is running the solenoid is allowed to be open. There are way more complicated ways to do it, but that's the easiest

 

[clownfishsydney]

I just use a welding oxygen regulator. I then restricted the flow as first it provided too much oxygen and too little way to adjust the oxygen percentage. I got a stainless steel screw that fitted inside the outlet and then filed a bit off the shaft till I got a much less flow. I can now make nitrox to within about 0.5% each and every time just by changing the outlet pressure on the regulator (took a few trials to work out the various % for a variety of PSI settings).