Nitrox stick flow meter rate?

[abnfrog]

I was going to use a stick I then got talking to jordair they say DONT do it ,,(I started a thread about it here ) they actually changed my mind I suggest you call them in bc Canada and ask advice , he convinced me after 25+ years of blending (and being a advanced blending instructor )

 

[RayfromTX]

keeping tanks O2 clean among other high pressure o2 issues kept me on the nitrox stick program.

 

[BRT]

I was going to use a stick I then got talking to jordair they say DONT do it ,,(I started a thread about it here ) they actually changed my mind I suggest you call them in bc Canada and ask advice , he convinced me after 25+ years of blending (and being a advanced blending instructor )

What was their reasoning?

 

[RayfromTX]

They said you should only pump nitrox through a compressor block specifically designed for the purpose. I've heard it from many manufacturers but I always wonder, from my ignorant point of reference, if the reason is because they are unable to control the O2 content and are unwilling to recommend the practice because of the chance that the wrong twist of a valve suddenly has you pumping 80% which would be a problem. Afterward the investigation would be hard pressed to determine what the mix was at the time of the explosion.

 

[tbone1004]

@abnfrog I remember that thread and I remember that your tech never actually said why. He may have convinced you, but you didn't relay to us why other than there was a nitrox specific block and left it at that.
There are tens of thousands of cubic feet of EAN32 being pumped through standard Bauer compressors every single day and I have yet to hear of one blowing up as long as it was done properly *i.e. O2 shutoff tied to the compressor shutoff so you don't blow straight o2 into it*

So please enlighten us here on what convinced you to stop continuous blending?

From Bauer's website
Same blocks, they just undergo an ultrasonic cleaning step. You have filter stacks and coalescers for oil removal, not concerned. It also doesn't stop oil going past the rings
Lube is all O2 compatible which can be done on any compressor at service time. That said, we are talking about sub 40% nitrox mixes that don't require O2 cleaning, so as long as you have an O2 shutoff to not dump pure O2 into the thing when it shuts off, all is well in the world.
Temp monitoring and maybe some extra cooling capacity that the other models don't have. That's nice, but you can hit it with an IR thermo if you're concerned. If you're really worried, for about $200 and a few hours of your time you can build a relay system with a raspberry pi that has however many thermocouple probes you want that can be tied to the shutoff circuit for the compressor. Bit ghetto compared to Bauer's solution, but just as effective.


edit: here's the thread for anyone curious. Really nothing good in here other than people trying to CYOA/Bauer getting TUV SUD certification on those blocks
nitrox blending

 

[abnfrog]

without rehashing this all again ,,,he said the block was different I asked stronger ? cleaner ? he told me it was completely different ....then said he had over 10 on the bench for rebuild because people continuously blended threw them ...so take it for what its worth and you paid for the advice ...im heeding it as I don't have another 7k for a rebuild

 

[tbone1004]

without rehashing this all again ,,,he said the block was different I asked stronger ? cleaner ? he told me it was completely different ....then said he had over 10 on the bench for rebuild because people continuously blended threw them ...so take it for what its worth and you paid for the advice ...im heeding it as I don't have another 7k for a rebuild

per the Bauer website they are the same just a bit cleaner. Something tells me he was trying to sell you a new compressor block.... 7k for a rebuild sounds excessive as well, even for the big compressors. We pay about 2k for our 15cfm bauers to be rebuild and they have ean32 going through them. Roughly 3000cf/day each

 

[rddvet]

I use the Dwyer VF series flowmeters (VFB-67-BV-PF-SPCL-VIT). $95 for an oxygen clean, viton o-ring version, and they make them in a bunch of different sizes. Supply it with a welding regulator and you can flow as much oxygen as you want with a great deal of control: Series VFA & VFB Visi-Float® Flowmeters Product Configurator | Dwyer Instruments

Keep in mind that flowmeters are calibrated assuming that you're flowing into the atmosphere and the displayed LPM is only ballpark. You would need to be able to measure the output temperature and the actual pressure to get an exact figure. The bigger challenge to accuracy is that the compressor's input isn't flat and you'll need to adjust the flow slightly over the course of a fill to maintain your desired nitrox percentage. Or you can "set it and forget it", depending on how much your care about your fills hitting your desired nitrox percentage. I aim for within 2/10 of a percent because I geek out on the whole process. Many (including agency standards) are quite content if the final blend is within 1-2%.

Anyhoo...

At 5 CFM input, you need roughly 15 LPM for 32% and 27 LPM for 40%.
At 3.5 CFM input, you need roughly 11 LPM for 32% and 19 LPM for 40%.

Dywer makes flowmeters with 3-25 LPM scales, 6-50 LPM scales and 10-100 LPM scales. Most of us garage guys are going to want the 3-25 LPM version.

You can also order the Dwyer flowmeters with an arbitrary scale and not worry about the LPM display. It's more important that the bore is correctly sized to your compressor input. If you tried to use the 10-100 LPM flowmeter on a 5 CFM compressor, you'd have use a combination of low input pressure and low displayed LPM to get your desired 15 LPM flow rate to produce 32%. Fine adjustment would be very difficult, and your fine control would come almost entirely from the regulator pressure instead of the flowmeter. Better to use a 3-25LPM flow meter and gain a bit more accuracy.

On my compressor, 25 PSI on the welding regulator = 32% at 11 LPM displayed, and 40% at 20 LPM displayed. Pretty close to the expected flowrates, but more importantly, in the middle of the flowmeter's range and the welding regulator's most stable output pressures (15-40 PSI, per manufacturer). Adjustments are easy.

Have fun and don't blow yourself up.

-B

This is the perfect answer you need. I was going to say something along these lines and recommend a Dwyer by would not have done it as well nor done a single bit of math.

As for not needing one it is correct. You absolutely don't need a flowmeter but to me it is safer and much better. You can really fine tune your flow rate and most importantly are way less likely to slip up and shoot a wallop of oxygen in your compressor an make it go boom. Adding an oxygen solenoid in the mix is even better

 

[BRT]

This is the perfect answer you need. I was going to say something along these lines and recommend a Dwyer by would not have done it as well nor done a single bit of math.

As for not needing one it is correct. You absolutely don't need a flowmeter but to me it is safer and much better. You can really fine tune your flow rate and most importantly are way less likely to slip up and shoot a wallop of oxygen in your compressor an make it go boom. Adding an oxygen solenoid in the mix is even better

Anybody mixing nitrox in a stick without a solenoid is really asking for trouble.

 

[RayfromTX]

This is a short video showing the simultaneous blending of 32% nitrox into the bank tanks while transfilling four scuba tanks through the fill panel.