blending over 40% nitrox with a stick

[ALAN243]

I have a rebreather and like to use 60% in my tanks pp blending is a pain and was wondering if anyone knew if it was possible to blend over 40% with a stick, everything I seen says 40% is the max.. local store here has a membrane but can only pump 40% also, so that leaves that out. any help Thanks

[agstreet]

The problem with continuous flow blending (which includes using a membrane) is that it's pretty hard on the compressor. You should be using an oilless compressor (such as a RIX) for CF blending, but a lot of shops don't. Unless you've got a compressor rated for pumping pure O2, you're better off PP blending mixtures above 40%.

Alan

[sciencediver1]

Its not that it's hard on the compressor so much. Coltri which makes the compressor blocks for Max-Air, and Nuvair as well as others, says CF blending will not void their warantee as long as the proper oil is used, such as Nuvair 455 which is rated for CF blending up to 40%. The biggest problem going higher is the risk of an explosion within the compressor block. Oxygen gets pretty unstable at high pressure so obviously the higher the fO2, the higher the risk of an explosion. You're stuck with PPB above 40%

[peteybee]

I have a rebreather and like to use 60% in my tanks pp blending is a pain and was wondering if anyone knew if it was possible to blend over 40% with a stick, everything I seen says 40% is the max.. local store here has a membrane but can only pump 40% also, so that leaves that out. any help Thanks

I never thought PP was a pain. Oh well, from the manual. Your choices are re-circulated over the membrane which will bring you up to a max of 80% o2 but you will need an oil free compressor. You could use a continuous blending method where the os wont go over 2 bar pre compression and again you will need an oil free compressor, but you can reach a theoretical 80%. The only other alternative is to use PP which is the easiest and the cheapest solution. Using a stick? Well, I would continue with PP.

Pete

[sciencediver1]

I agree, above 40% use PPB. Just remember to add 2-5% less O2 then the theoretical gas laws recommend, and Slow, Slow, SLOWER...let cool fully, top up to the numbers less the fudge, cool, then top off as needed with air. Craig