How do you properly bleed air out of nitrox tanks

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OP
Nitrox_DiverNY

Nitrox_DiverNY

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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.
It just made me a bit uncomfortable having 2 full tanks that would have most likely have sat for the rest of the winter. I know there’s nothing to worry about but id rather be safe then sorry. Thanks for the feedback!
 

grf88

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Aluminum tanks are best left full or with only about 500 psi in them. In a fire the full one will blow the burst disk before the aluminum weakens and lets go. With low pressure they will not be much of an explosive risk even if the burst disk doesn't let go. I do not know if steel has the same issue.
 

elan

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It just made me a bit uncomfortable having 2 full tanks that would have most likely have sat for the rest of the winter. I know there’s nothing to worry about but id rather be safe then sorry. Thanks for the feedback!
Nothing should happen to them, I dove a couple of stages that we filled 4 years ago, tested for the o2 content compared with the label on the tank made sure it did not change. No issues
 

wedivebc

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Can someone explain to me why draining a tank will cause moisture to form inside a tank? When the tank is filled the air will contain a maximum dew point of -50 degF. While the tank will get cold and atmospheric moisture will collect on the outside of the tank, the very small quaintly of moisture inside should not be a problem.
 

Alekseolsen

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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.


Small edit: If you are doing partial pressure Blending, either at a ****** shop, or for a very different mix than previously used, you may have to drain the tanks.
 

Lostdiver71

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You should not have to drain a tank for partial pressure blending. If the shop that you are going to can't figure out the math or use an app to figure out what gases to add to your tank to get the proper mix they probably shouldn't be filling nitrox. We used to actually have to do algebra to figure out the proper mix, now you just plug in what you have and what you want to an app and it tells you what to add to get the mix you want. I have had tanks sit for several years before using them, as long as they analyze properly you will be fine.
 
https://www.shearwater.com/products/perdix-ai/

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