Suggestion for Nitrox Stick O2 flow

[Marten Deinum]

Hi,

Recently we decided to build a Nitrox stick to be able to fill Nitrox up to 40%. All this is being fed into a compressor that produces 400l/m. We have some medical flow regulators that go up to 18l/m but that isn't near enough to get a decent Nitrox mix. Some calculations show that we would need to go to around 44l/m to get 32%. (which makes sense as we need to add 11% of 400l is 44l).

Now as our flow regulator doesn't get till 44l/m (nor am I sure we should want that kind of flow with pure O2), are there any best practices to make this happen. Ofcourse we can put multiple O2 tanks in there, feed multiple lines into the nitrox stick etc. But I was wondering if there would be a cleaner solution (or maybe my fear of high flow isn't warranted and that there are O2 flow regulators which can go upto 76l/m to get 40%).

Thanks.

 

[tbone1004]

Your math is a bit off for the blend ratios, and unfortunately in the wrong direction.

For EAN32 you need to add ~14% of the mixture as O2, and for EAN40 that's about 24%

If you have a 400lpm compressor then that's ~56lpm to get to EAN32 and 97lpm for EAN40

There are plenty of 100lpm flow meters out there that can handle that without issue which is ideal.

 

[Marten Deinum]

My calculations were off indeed, thanks for correcting me.

I tried to find O2 flow regulators for higher flows but I couldn't find those, as that would indeed be ideal. Could you share a link?

 

[Snusmumrik]

find O2 flow regulators for higher flows but I couldn't find those, as that would indeed be ideal.

Use welding regs.

 

[grf88]

I needed to find a higher flow O2 meter for my set up for higher mixes and just added another in parallel.

 

[TravisD]

On my 300-ish lpm compressor, I'm using a welding reg into another adjustable reg into a needle valve. The first reg stage get set to 60-ish PSI which makes the 2nd reg stage more stable. 2nd stage is set to about 15psi with the needle valve cracked open. The needle valve tends to make big changes when adjusted, while adjusting the 2nd stage reg nets finer adjustments. The key is having some flow restriction for the regulator to work against.

Prior to adding the 2nd reg stage and the needle valve I had to adjust frequently. The 2-stages + restriction is much more stable, though it does need adjustment as the compressor flow changes across the fill pressure range, and it changes when the condensate drains open. I don't really care about measuring the flow since adjustment is all based on the O2 reading coming out of the stick anyway.

 

[tbone1004]

My calculations were off indeed, thanks for correcting me.

I tried to find O2 flow regulators for higher flows but I couldn't find those, as that would indeed be ideal. Could you share a link?

Not sure if links work for Netherlands

High quality welding Oxygen Regulator

https://a.co/d/1pJyiEz

This has a solenoid connected directly to the outlet tied to the compressor

Dwyer 10-100lpm flow meter. They also have 20-200lpm if you have a larger pump, but the 10-100 in this case will suffice.

https://a.co/d/bNcvVmx

Now, this setup will still need semi-regular adjustments as the Victor regulator is single stage so it's outlet pressure is variable across the tank pressure.
If you are a really high volume fill station I would recommend spending the extra money for the 2-stage regulator, though it is 4x the price. This stabilizes the outlet pressure to where almost no adjustments are needed.

Amazon.com

The extra fancy would be an automatic stick that is actually using servo valves to adjust the needle valves for accurate mix, but those are only cost justified in shops that are running nitrox for multiple hours every day.

 

[Doc Harry]

Use welding regs.

BINGO

 

[Tracy]

On my 300-ish lpm compressor, I'm using a welding reg into another adjustable reg into a needle valve. The first reg stage get set to 60-ish PSI which makes the 2nd reg stage more stable. 2nd stage is set to about 15psi with the needle valve cracked open. The needle valve tends to make big changes when adjusted, while adjusting the 2nd stage reg nets finer adjustments. The key is having some flow restriction for the regulator to work against.

Prior to adding the 2nd reg stage and the needle valve I had to adjust frequently. The 2-stages + restriction is much more stable, though it does need adjustment as the compressor flow changes across the fill pressure range, and it changes when the condensate drains open. I don't really care about measuring the flow since adjustment is all based on the O2 reading coming out of the stick anyway.

This is the set up I came up with years ago. It holds steady from full to empty. The cheapo second regulators usually last about 3-5 years running Oxygen.

 

[TravisD]

Tracy, I’m pretty sure that my setup is a direct result of your setup, by way of recommendation passed along by @rob.mwpropane - I definitely did not come up with that setup independently!