My Nitrox Stick build

[BRT]

the oil vapor lubricates the valves and top of the pistons.

This!

 

[rjack321]

One question I had recently, was "is it feasible to use an air pump to supply gas from the bottom/outlet of the nitrox stick to a Divesoft analyzer". It seems to me that, if doing that, I could put helium and O2 in at the top of the stick, measure it at the bottom (adjust flowrates as necessary) and mix trimix right in the one stick. Is there a downside to that I'm not aware of. Maybe something @tbone1004 knows of or someone else?

yes its quite possible to use a ~2L/min sampling pump to draw off gas for analysis. Parker distributes some by a company called hargraves. HARGRAVES Brushless DC Miniature Diaphragm Pumps : Parker Hannifin, Precision Fluidics Division - EngNet USA

The divesoft analyser is annoyingly sensitive to flow rate unfortunately so you may want to use a different helium analyzer.

 

[jlcnuke]

yes its quite possible to use a ~2L/min sampling pump to draw off gas for analysis. Parker distributes some by a company called hargraves. HARGRAVES Brushless DC Miniature Diaphragm Pumps : Parker Hannifin, Precision Fluidics Division - EngNet USA

The divesoft analyser is annoyingly sensitive to flow rate unfortunately so you may want to use a different helium analyzer.

Thanks, I got the professional flow limiter and using that it's really easy to use the Solo analyzer. I'd have to rig up a connector to go to a female din fitting though to use it. Something I may consider in the future if I find myself doing trimix dives more frequently.

 

[rjack321]

Thanks, I got the professional flow limiter and using that it's really easy to use the Solo analyzer. I'd have to rig up a connector to go to a female din fitting though to use it. Something I may consider in the future if I find myself doing trimix dives more frequently.

You won't be able to do pre-compressor monitoring for the mix with the included flow limiter. That requires HP inlet gas. You could use it to monitor at the compressor outlet, but you will be continually "chasing the mix" because of the lag between adjust inlet gases and reading the outlet %ages. And you have to continually adjust as your pump pressure rises from 0 to 3000+psi. Moreso with trimix than nitrox due to the increasing blow by.

Between the outlet of your stick and inlet to your compressr have gas at ambient pressure. The hargraves pumps are going to create ~2lpm at ~3psi.

Honestly for oil lubed compressors its easier to just use it as a low pressure helium pump. Put 100% through it at <2500psi like it was a booster and the blowby is no big deal. Turn off the helium and top with 32%. Done.

 

[iain/hsm]

Honestly for oil lubed compressors its easier to just use it as a low pressure helium pump. Put 100% through it at <2500psi like it was a booster and the blowby is no big deal. Turn off the helium and top with 32%. Done.

Let me get this right.
So the plan is to take perfectly clean dry certified and prestige expensive helium.
A noble gas out of a clean high pressure cylinder and then to blow it all into an oily air compressor
loosing half of it with blow-by leaks and loses?

Then cooking the remaining other half using this oil lubricated compressor designed to compress ambient air rather than a clean dry gas at the intake and so contaminating what little gas remains that makes it past the compression process inside this oily air compressor.. Then after compression only to have to clean it up all over again except now its through a cheap scuba compressor filter designed for wet air adsorption, than dry gas filtration and this is the plan?

What can possiby go wrong with this idea. Heck why don’t all the gas suppliers use this method of compression, Makes me wonder if this is not just another variation on a cave fill from those cave fill country farmers ?

But its easy I will give you that. And easy to make.even for a farmer ...........Death gas for cutie in a cave fill.
Whats not to like. Iain

 

[njaimo]

...I may be missing understanding something, but the discussion seems to me merely theoretical. Practically, pre-mixing and storing 32% and then running He through a compressor, all just to avoid the use of a booster seems a waste of time, effort, and money to me. If diving trimix, one needs to do deco, which requires 100% O2 (not discussing 80% vs 100% O2 deco here). So for the DIY'er this will require a booster to reach 3,000 psi fills of the 100 O2 deco bottle (or rebreather bottles). One can only get this with an oxygen clean booster. One can say 3,000 psi is not needed for a given dive, and I realize that, but still supply O2 usually only comes in 2200 psi, so at some point boosting is necessary even to get to 2200 psi or so, unless you have a cascade (and are paying yearly cylinder fees). One is not limited to a $2K or more Haskel boosters anymore.

IMO partial pressure blending, using "real gas law" calculations, temperature corrected to account for heat of compression (Baltic Blender), and a booster is the simpler, cheaper, less labor intensive, and I would suggest more accurate way. ...my two cents... Given I dive with one or two buddies at the most, I do not even use a mixing stick anymore to make nitrox, and just partial blend nitrox or trimix in my garage, using a garbage can full of water to keep my cylinders cool.

BTW, I do not believe my 4.2 CFM Kidde recycles blow-by. Maybe Frogman can provide an authoritative answer.

 

[njaimo]

...should have written in there that the booster thus needed for O2 is then used to boost He too.

 

[njaimo]

…a sensible alternative is to mix air and He with mixing stick, and then go to your LDS to use booster to add the needed O2 to complete the Trimix, and for deco.

 

[BRT]

...I may be missing understanding something, but the discussion seems to me merely theoretical. Practically, pre-mixing and storing 32% and then running He through a compressor, all just to avoid the use of a booster seems a waste of time, effort, and money to me. If diving trimix, one needs to do deco, which requires 100% O2 (not discussing 80% vs 100% O2 deco here). So for the DIY'er this will require a booster to reach 3,000 psi fills of the 100 O2 deco bottle (or rebreather bottles). One can only get this with an oxygen clean booster. One can say 3,000 psi is not needed for a given dive, and I realize that, but still supply O2 usually only comes in 2200 psi, so at some point boosting is necessary even to get to 2200 psi or so, unless you have a cascade (and are paying yearly cylinder fees). One is not limited to a $2K or more Haskel boosters anymore.

IMO partial pressure blending, using "real gas law" calculations, temperature corrected to account for heat of compression (Baltic Blender), and a booster is the simpler, cheaper, less labor intensive, and I would suggest more accurate way. ...my two cents... Given I dive with one or two buddies at the most, I do not even use a mixing stick anymore to make nitrox, and just partial blend nitrox or trimix in my garage, using a garbage can full of water to keep my cylinders cool.

BTW, I do not believe my 4.2 CFM Kidde recycles blow-by. Maybe Frogman can provide an authoritative answer.

If you think it does not recycle blow-by, where does the blow-by exit the compressor?

 

[njaimo]

...it has a crankcase vent at the bottom which sometimes leaks a drop of oil