Nitrox stick controls question- kinda a follow up to the my last thread

[tbone1004]

@jlcnuke low pressure O2 does not need viton o-rings. Second stages at 150psi don't need it, so a flowmeter seeing 10-20psi certainly won't

 

[jlcnuke]

@jlcnuke low pressure O2 does not need viton o-rings. Second stages at 150psi don't need it, so a flowmeter seeing 10-20psi certainly won't

Good point. That makes things simpler lol

 

[rjack321]

Tbone, Rslinger rddvet, and prid1279 thanks for your input. I think I'm going to build one with PVC and the wiffle golf balls (since I already have a bunch of them). I think I'll just monitor it and shut down manually if there is an issue with O2%, but I think I'll still wire a solenoid to trip closed if the compressor goes offline (just to be safe). So now I'm looking for adjustable flowmeters, but it looks like to get 32% I'll be at ~15 lpm (plus or minus a bit), so the basic medical ones that only go to 15 lpm will be a bit low range. The others seem to all have rubber o-rings involved, so may have to rebuild those with viton if I can't find one rated for O2 that can handle a bit higher flow rate (ideally 0-30 lpm or equivalent seems like it would be best).

I'll look for something like that later today.

For monitoring, I think I'd be fine to connect my divesoft solo analyzer to the outlet (I'll 3d print an adapter to connect the pro limiter valve to the outlet from the stick and just run that to the solo analyzer).

Thanks for the help everyone

The "15lpm" medical O2 regs on ebay are so cheap that I would first try one before getting something more expensive. Their flow rates are also inaccurate - to be expected for $20. Mine is running at "12" LPM to make 32% at 3.5cfm per minute. So I have one with an oversized orifice or the IP is a bit high. Either way its been like this since 2003 and works fine to make 32%.

You can also bore out the orifice with the worlds tiniest drill bit and use these flow regs to convert leftover 50% into 32% since topping up 50% bottles is kinda sucky.

Most of them have buna parts which is standard in other fields (aviation and medical)

 

[grf88]

I have a balanced O2 reg and a cheap adjustable flowmeter. You need repeatability more than accuracy with the flowmeter and I found the readily available one fine. I also use the scouring pad at the bottom of the stick and find it helps with the mixing.

 

[rddvet]

This is the dwyer flowmeter I use after my welding reg. It's 0-3scfm. I use it on a Bauer K14.

 

[macado]

I'm using a good quality O2 welding regulator and a cheap 2-20LPM Chinese flowmeter on my nitrox stick. On my O2 welding regulator I have it set to something low like ~30-40psi. I also have ~50psi OPV here so I don't accidently run higher pressure through my flowmeter. I have a Divesoft analyzer on the output side of my compressor which I compare to the analyzer on my nitrox stick. I found a cheap Maxtec O2 medical analyzer on fleeBay for like 40 bucks. I cut the connector off and soldered another one on it. That's what I am using at the bottom of my nitrox stick before it goes into my compressor intake.

For my mixing tube/chamber I'm using a clear static mixer (CLR-200-2ST-MM40 clear 2" MPT ends length 20" from TAH Bell Static Mixers - StatiFlow Clear Mixers It's kind of overkill for this application I just bought it because I honestly like how it looks.

I also own a Dwyer flowmeter (RMB-52D-SSV Flowmeter, range 4-50 SCFH/2-23 LPM air) which is much higher quality but my little Chinese one is working fine so I haven't replaced it yet. I have several friends who had the Chinese one but weren't happy with the accuracy so they switched to the Dwyer one. If I were doing it all over again I would go with the Dwyer flowmeter. Once my Chinese one starts giving me trouble I will replace it.

https://www.amazon.com/gp/product/B07DNX1Z7K

Dwyer RMB-52D-SSV Flow Meter, 5" Scale, 4-50 SCFH/2-23 LPM Air, SS Valve

It's all pretty accurate for me. I'm using a Alkin W31 (~3.6cfm / 100lpm) compressor. I never really mix anything other than 32% so rarely have to adjust things too much. For example, the math for 32% is 14.03% of the gas has to be pure O2 into the nitrox stick.
3.6cfm x .1403 = 0.50508cfm
50508cfm = 14.30227308276lpm so you can see where I got 14lpm a minute from on flowmeter.

Coincidentally, this is exactly what my cheap Chinese flowmeter reads when pumping 32% on my Alkin.

The biggest changes I made was I replaced the clamp-on cold air intake filter with a solberg filter silencer on the top of my Nitrox stick and I added a solenoid on my welding regulator to shut off flow of O2 when compressor is not running that is wired into my accessory port on my motor starter.

EDIT: Here is hopefully a clearer picture of the nitrox stick. There are obviously many different variations of this design but mine has been working well with no real issues. Instead of using a t-piece at the bottom. I just used an M16 x 1mm tap directly into the PVC. The O2 sensor screws into place and seals with an o-ring on sensor itself. I also ended up adding a longer section of PVC to the top to that O2 was injected further into the nitrox stick. Honestly I'm not sure if it was needed since I never noticed any issue before. My compressor has a 1" intake so I am short section of 1" hose that goes directly into my nitrox stick with a 2" to 1" reducer to barb fitting on the bottom. I kept this section as small as possible to minimize resistance. It's about ~32" (81cm) from my compressor intake to the nitrox stick since my compressor sits right next to it.

 

[rddvet]

I'm using a good quality O2 welding regulator and a cheap 2-20LPM Chinese flowmeter on my nitrox stick. On my O2 welding regulator I have it set to something low like ~30-40psi. I also have ~50psi OPV here so I don't accidently run higher pressure through my flowmeter. I have a Divesoft analyzer on the output side of my compressor which I compare to the analyzer on my nitrox stick. I found a cheap Maxtec O2 medical analyzer on fleeBay for like 40 bucks. I cut the connector off and soldered another one on it. That's what I am using at the bottom of my nitrox stick before it goes into my compressor intake.

For my mixing tube/chamber I'm using a clear static mixer (CLR-200-2ST-MM40 clear 2" MPT ends length 20" from TAH Bell Static Mixers - StatiFlow Clear Mixers It's kind of overkill for this application I just bought it because I honestly like how it looks.

I also own a Dwyer flowmeter (RMB-52D-SSV Flowmeter, range 4-50 SCFH/2-23 LPM air) which is much higher quality but my little Chinese one is working fine so I haven't replaced it yet. I have several friends who had the Chinese one but weren't happy with the accuracy so they switched to the Dwyer one. If I were doing it all over again I would go with the Dwyer flowmeter. Once my Chinese one starts giving me trouble I will replace it.

https://www.amazon.com/gp/product/B07DNX1Z7K

Dwyer RMB-52D-SSV Flow Meter, 5" Scale, 4-50 SCFH/2-23 LPM Air, SS Valve

It's all pretty accurate for me. I'm using a Alkin W31 (~3.6cfm / 100lpm) compressor. I never really mix anything other than 32% so rarely have to adjust things too much. For example, the math for 32% is 14.03% of the gas has to be pure O2 into the nitrox stick.
3.6cfm x .1403 = 0.50508cfm
50508cfm = 14.30227308276lpm so you can see where I got 14lpm a minute from on flowmeter.

Coincidentally, this is exactly what my cheap Chinese flowmeter reads when pumping 32% on my Alkin.

View attachment 669708
View attachment 669709

The biggest changes I made was I replaced the clamp-on cold air intake filter with a solberg filter silencer on the top of my Nitrox stick and I added a solenoid on my welding regulator to shut off flow of O2 when compressor is not running that is wired into my accessory port on my motor starter.

EDIT: Here is hopefully a clearer picture of the nitrox stick. There are obviously many different variations of this design but mine has been working well with no real issues. Instead of using a t-piece at the bottom. I just used an M16 x 1mm tap directly into the PVC. The O2 sensor screws into place and seals with an o-ring on sensor itself. I also ended up adding a longer section of PVC to the top to that O2 was injected further into the nitrox stick. Honestly I'm not sure if it was needed since I never noticed any issue before. My compressor has a 1" intake so I am short section of 1" hose that goes directly into my nitrox stick with a 2" to 1" reducer to barb fitting on the bottom. I kept this section as small as possible to minimize resistance. It's about ~32" (81cm) from my compressor intake to the nitrox stick since my compressor sits right next to it.

View attachment 669713View attachment 669714

I like how you did the divesoft. Smart workaround. If you talk to Divesoft they recommend a lp aquarium pump to pump the gas to the unit (or that's what they said 5 years ago when I asked).

I also have a opv on the oxygen before the flowmeter just to be safe.

 

[macado]

I like how you did the divesoft. Smart workaround. If you talk to Divesoft they recommend a lp aquarium pump to pump the gas to the unit (or that's what they said 5 years ago when I asked).

I also have a opv on the oxygen before the flowmeter just to be safe.

Thanks. It make everything pretty modular. I didn't want to deal with an aquarium pump but I suppose that would be the solution if you were using one on the nitrox stick itself. I have a secondary filter stack (shown in pictures above) that connects to my 5-port manifold. The manifold has line valves and parker QD fittings so I can quickly swap and move whips around. I use the same fittings on my booster.

For those that are curious - It's Female DIN to 1/4 NPT fitting that connects to another Parker QD fitting on my 5-port manifold. It's available from Global Scuba (45186 Female DIN to Female Pipe Adapter, Brass: Provides a female 300 Bar DIN connection to a ¼ female NPT pipe thread. 4,500 psi service, chrome plated brass.) I can also use this adapter to fill T bottles with a DIN whip.

From here I just use the Divesoft professional flow limiter to sample gas coming directly out of my manifold (after my filter stacks). It's honestly a bit overkill but it works for secondary analysis. I'm pretty happy just trusting the flowmeter with nitrox analyzer at the end of my nitrox stick but having the divesoft analyzer at the end can be helpful to see when nitrox arrives at your whips (after pumping air or other gases) or to troubleshoot O2 leaks / losses in the system.




Divesoft.com

 

[FLDVR]

Mix sticks work great, the Trihunter is great but as mentioned very pricey. One thing you can never do
is walk away, its like fiddling with radio dials you have to stay on top of the drift. The Trihunter 2.0 electronics take care of this to some extent. I ended up with the Nardi TTmix, the Trihunter mixing stick is gathering dust. A Divesoft on the output like Mike's is the way to go!

 

[jlcnuke]

Thanks for the advice everyone

I ended up making the stick, and posted what I did here.