Gas mixer inside a nitrox stick... options

[estresao]

Hi everyone,

I've finally got a brand new compressor (Bauer PE-100 single phase) and I'm now facing the next step, which is constructing a trimix blender stick.

I'm not sure yet about the final design so I'm reading all I grab to learn. I'm still reading the famous Oxihacker and asking colleagues who already have one to take ideas. One of the topic I'm curious about is the mixer design inside the stick and I've found several approaches:

- The baffles one, based on the Oxyhacker, very simple having only 4 baffles which makes the air enter in "zig zag"
- Ping Pong balls... I've been told they remove humidity and could be a good options for those which lives lose to de coast (which is my case).... I don't know whether that's true, I've also been told they don't actually mix gases, which also don't get... any input here?
- Practice golf balls: I guess this one is similar to the ping pong one
- Aquarium Bio Balls: I guess this is yet another version of the balls approach... is there any advantage with this one?
- The static mixer, which looks nice but not sure whether it worth the money in this case.

Is there any recommended approach? would one of the balls variants be good enougth? should I go for the ping pong approach because the humidity?

 

[nickbutcher]

My homemade stick uses a bundle of stainless steel wool as the baffle and it works perfectly.

It’s a length (approx 1m) of 30mm plastic pipe with a threaded hose barb screwed in near the top. The stainless wool is just shoved in the pipe at and below the O2 entry.

I tapped a 1/2” BSP thread into the inlet of the compressor (mine is also a PE100) and made an adaptor that includes the t-piece from a Vandagraph O2 analyser so I can monitor the mix.

Whole thing cost less than a tenner.

 

[estresao]

My homemade stick uses a bundle of stainless steel wool as the baffle and it works perfectly.

It’s a length (approx 1m) of 30mm plastic pipe with a threaded hose barb screwed in near the top. The stainless wool is just shoved in the pipe at and below the O2 entry.

I tapped a 1/2” BSP thread into the inlet of the compressor (mine is also a PE100) and made an adaptor that includes the t-piece from a Vandagraph O2 analyser so I can monitor the mix.

Whole thing cost less than a tenner.

Very interesting.... and chip. Do you mix trimix as well?

Also interesting the diameter of the stick, I was thinking in using a 50mm PVC pipe (which happens to be already in my house because another stuff), but I guess is nothing cannot be managed stuffing it with more wool

 

[happy-diver]

34.97€ |2

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[rob.mwpropane]

I use a 2' section of 2" pvc that has 3D printed spirals placed in it. Very cheap to build. The spirals screw together and alternate.

Nitrox Stick Mixer_2" PVC by RobERob

Nitrox stick mixing insert. There are 2 files, they'll change the way the air spirals through to mix things up. I have this in a 2" PVC 24" long with a Solberg filter on top. Works great, very inexpensive solution, even cheaper than whiffle balls. I printed either 3 or 4 to fit in a 24" section...

www.thingiverse.com

I have not mixed trimix yet, but I think about doing it. I am in the process of building one of these. It adds 1 more mixing stick and another O2 sensor.

GitHub - divetools/Gas-Blending: Python apps to assist with Gas Blending

Python apps to assist with Gas Blending. Contribute to divetools/Gas-Blending development by creating an account on GitHub.

github.com

All this is under ~ $300 and a pretty solid setup. The raspberry pi screen is just a really nice display to organize everything on one screen, but even then you could get away without it.

 

[estresao]

@rob.mwpropane Very interesting the as Blending application, I'll have a look to see how can I use it. I have not a 3D printer because I'm software engineering and need to peel my butt off the chair so, this kind of things doesn't help, but I'm pretty sure I can use the application. If I had one I'd probably go for a design based on that: Static mixer - Wikipedia

34.97€ |2

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

happy-diver, this is a good one, but not sire whether it worth pay 30 EUR... not discarded, just not sure.

 

[nickbutcher]

Very interesting.... and chip. Do you mix trimix as well?

Also interesting the diameter of the stick, I was thinking in using a 50mm PVC pipe (which happens to be already in my house because another stuff), but I guess is nothing cannot be managed stuffing it with more wool

I don’t mix trimix using the stick, too much of a ballache. I just add nitrox to helium (or whatever is in my trimix bank) to get whatever ballpark mix I need. I dive a CCR so don’t worry about accurate mixes. As long as the helium is somewhere close to giving me an END of <25m, I’m happy.

As for the pipe I used, I was in the same boat as you - it was what I had in my workshop at the time.

 

[rjack321]

- The baffles one, based on the Oxyhacker, very simple having only 4 baffles which makes the air enter in "zig zag"
- Ping Pong balls... I've been told they remove humidity and could be a good options for those which lives lose to de coast (which is my case).... I don't know whether that's true, I've also been told they don't actually mix gases, which also don't get... any input here?
- Practice golf balls: I guess this one is similar to the ping pong one
- Aquarium Bio Balls: I guess this is yet another version of the balls approach... is there any advantage with this one?
- The static mixer, which looks nice but not sure whether it worth the money in this case.

Is there any recommended approach? would one of the balls variants be good enougth? should I go for the ping pong approach because the humidity?

Plastic ping pong balls will not change the inlet humidity at all. Nor will any of the other mixing baffles approaches. Think about it this way, the only way to reduce the humidity is to chill the inlet air until water drops out of the gaseous phase and drips away as a liquid...

Use whatever is cheapest and readily available that doesn't starve your compressor for air via a restriction. This is fairly easy to do, just use a mixing stick about 2-3x larger diameter than your compressor inlet. Also upside the hose and don't make it too long.

 

[estresao]

I ended up getting one of those static mixers @happy_diver suggested, but after some researches I agree it doesn't worth going very complex.

Now I'm working in an analyzer similar to what Rob showed based on ESP32 microcontroler (Arduino evolution).... 1st step, analyzing nitrox, is almost done (not very complex) and leaving the 2nd step (one more O2 sensor for He mix) for later. If I get time there would be some chance I "play" with solenoids so that the microcontroller control the mix.... not sure yet about that.