Filling doubles with nitrox on a boat...

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Scubaroo

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Got a silly question (always worth asking)...

One of the local boats I dive from does nitrox fills onboard. I'm looking at putting a set of doubles together, but they're AL80's - not large enough to do two dives from for my typical profile. So I would be looking at getting a fill between dives from the boat's compressor (they do continuous blend filling I believe).

How accurate would gas analysis be after getting a fill? Assuming you're only filling through one post with the isolator open, is the gas being pumped going to mix sufficiently in BOTH tanks? Say I had EAN32 from a shop in the tanks for the first dive, used half, then got a fill from the boat of EAN36 (you kinda get what they give unless you expressly ask for a lean mixture where they top off with air), is the EAN36 going to find its way evenly into both tanks? Should I analyze from both posts? I realize that when two gases are mixed, they evenly disperse, but how effective is this through the isolation manifold from one tank to another?
 
IMO, at any reasonable depth and exposure time it would not make any difference. I have never tested other than on one post.

MD
 
These are 3300psi tanks... but I think a crew member told me they could fill up to 4000psi once - but maybe only air, not nitrox.
 
to check with the boat. Considering the fact that some shore based shops have trouble hitting 3000psi. I used to have a pair of steel twin 50's, yes, they were small, but 100 cf. at 1800 psi, there was no trouble getting those puppies filled anywhere. The gas will mix, but check the O2 content on both posts and find out. IMO, the isolation valve shouldn't make any difference.
 
JeffAustin once bubbled...
IMO, the isolation valve shouldn't make any difference.
It will if it is closed when they fill you. :D

One great thing about doubles is that you don't leave an extra rock bottom in each one. You get to take the same rb with you on the second dive. You might be surprised... and get two dives off of your doubles.
 
They said they can do nitrox to about 3300psi hot.

Thanks for the reminder about rock bottom Uncle Pug - I'm just used to using a single 95cf on dives, and instantly compared that to 77.4cf per dive. But some quick math shows that I'm only using about 70cf-80cf of that 95cf per dive anyway.

Stuff it - for $50 plus hydros, compared to $660 or so for the PST E7-100 tanks I was hanging out for, I might as well put these together into doubles and just dive.
 

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