How do you properly bleed air out of nitrox tanks

[James79]

Since the 1st stage acts like a one way valve no ambient air

Just a heads up, 1st stages are closed by the IP reaching setpoint. Which means once tank pressure is below the set IP, it remains open and will not be serving as a one way valve. It will still be quite the restriction, and you still shouldn't get any air back into the tank (no pressure differential to drive it that way), but it is just an open path once the tank is below about 130 psi.

Respectfully,

James

 

[grf88]

Just a heads up, 1st stages are closed by the IP reaching setpoint. Which means once tank pressure is below the set IP, it remains open and will not be serving as a one way valve. It will still be quite the restriction, and you still shouldn't get any air back into the tank (no pressure differential to drive it that way), but it is just an open path once the tank is below about 130 psi.

Respectfully,

James

Absolutely correct but as you say it does provide a reasonable restriction.

 

[Still Kicking]

Well, it was my conclusion that the water was in the tank the instant it was opened up, there was no introduction of ambient air - or not enough to allow measurable water. Drain the steel tanks slowly

In that case you're getting very wet fills.

 

[johndiver999]

In that case you're getting very wet fills.

I don't think that is true. I don't want to argue with you and as already stated, I can't seem to get my head around a lot of condensation originating from presumably dry air, but I NEVER have water in my tanks - except when I tried to drain them fast and convinced myself that condensation was a non-issue.

So just be patient and drain them slowly.

 

[Jim Lapenta]

Hello all, a very basic beginnings question here, I don’t want to mess up anything. I was wondering what the proper procedure is for bleeding the air out of a nitrox dedicated tank. Is there anything special that needs to be done for bleeding out Nitrox? I know to leave about 500psi in but about how long should a Al80 take to get to 500psi without any moisture issues. Also is there any risk with bleeding a nitrox tank under 40% [like a fire], since it is a hyperoxic mix? Thanks for the help!!

Why drain it? There's no need to drain a cylinder down to 500 PSI. Storage? I have tanks sitting sometimes for 6 months with 2500-3000 PSI in them.
They do need to be drained for a VIP or hydro but not for just sitting around.
If you are worried about MOD then taking a cylinder with 500 PSI of say 32% and topping it off with air to 3000 will give you roughly 23% that has a MOD of 172 ft at 1.4 and 157 at 1.3 which is what I mix for.
There is no fire risk if you do drain it.
As someone else said, it's more annoying than anything. If you don't have some kind of muffler, wrapping a beach towel around the valve will help some.

 

[johndiver999]

Well if you are doing partial pressure blending, then they need to be completely drained before every single fill. Some shops don't want to deal with the complexities of adjusting the psi of oxygen to add to tank. Far simpler for the tank boys to completely dump each time. Another reason why banked pre-mix is so nice.

 

[Manatee Diver]

Good job I didn't make it out of iron pipe.

What you described isn't too different from making a silencer at home.

But I am glad that my joke still mostly made sense in Canada. I thought it would be another one of my jokes that I would have to explain.

 

[Tracy]

Well if you are doing partial pressure blending, then they need to be completely drained before every single fill. Some shops don't want to deal with the complexities of adjusting the psi of oxygen to add to tank. Far simpler for the tank boys to completely dump each time. Another reason why banked pre-mix is so nice.

Why would you need to drain the tank for partial pressure blending? I very very rarely do that.

 

[Nitrox_DiverNY]

A towel wrapped around the valve to muffle the sound works pretty good.

I did exactly that, saved my ears

 

[Nitrox_DiverNY]

I made a simple muffler that attaches to a BC hose. It is a piece of capped ABS tubing with multiple holes drilled in it and filled with plastic pot scrubbers. It has a BC nipple at one end. Since the 1st stage acts like a one way valve no ambient air can enter the cold tank to cause problems with condensation. It is also very quiet.

nice!