Nitrox Stick auto adjusting blender

[brysonjk]

What O₂ sensor are you using? What He sensor be appropriate?

No HE sensor. You use another o2 sensor. You calculate the displacement of o2 with helium. So if first mixing chamber sensor reads 10.5, you have 50% helium. Then you add o2 back in the 2nd mixing chamber. At least that is what I have been told. It has been a long time since I took the blending course and since I don’t have a reason to dive trimix up here I have since forgotten most of the more advanced calculations.

I’m using the old R-22D sensors out of my O2ptima CM. instead of throwing them away, I just trickle them down. 1 year in rebreather, 1 year in the mixing stick and my divesoft analyzer. Then garbage.

 

[TravisD]

Bringing this one back from the dead... Hey @brysonjk how as this been working out for you? I'm kind of curious about building one, but for my 11cfm compressor it looks like i'll need a much more expensive (mid-size) proportional valve so don't want to make a big $$ leap if it's not working out...

 

[BRT]

Bringing this one back from the dead... Hey @brysonjk how as this been working out for you? I'm kind of curious about building one, but for my 11cfm compressor it looks like i'll need a much more expensive (mid-size) proportional valve so don't want to make a big $$ leap if it's not working out...

I suspect you could feed the majority of the O2 through a simple solenoid valve and only fine tune with a proportional valve.

 

[brysonjk]

Bringing this one back from the dead... Hey @brysonjk how as this been working out for you? I'm kind of curious about building one, but for my 11cfm compressor it looks like i'll need a much more expensive (mid-size) proportional valve so don't want to make a big $$ leap if it's not working out...

I have been using this for years and I have been very happy with its operation. I have been working lately to modify the existing code to work on a Raspberry Pi. I have decided to turn it into a trimix blender but only have the nitrox side working so far.

If you want to use my old code, you could get aways with a slightly larger valve. If my math is anywhere close to correct (no guarantee since I'm going off some old memory), your compressor is about 300 L/min, if you want to boost that up to 40%, it would result in a o2 gain of 19% or 57 L/min. This valve will do that and more. You could just turn down the regulator to so that fully open it is at 40%. This become your upper safety. If the valve ever stuck open, this is the max o2 fed into your system.

High Flow Mini Valve - kellypneumatics.com

This mono proportional valve ensures virtually frictionless performance and longevity tested at over 100 million cycles. Click here!

kellypneumatics.com

The new version will ultimately look something like this and will be designed to run on the Raspberry Pi using a touchscreen. I'm using the old 7" Pie touchscreen.