Nitrox, HP, LP, DIN overfill?

[gmatt]

I'm new to this forum and Nitrox. I am going to sign up for Nitrox training in a few weeks. I've been diving since the early '80s and I've logged well over 600 dives. So I would not say I'm an expert by any means but when something dosen't sound right I've gotta ask some questions.

The set of tanks I'm using now are in for another hydro(third I think). I was in a local dive shop last night and I’m looking for a new set of tanks and a new regulator. I am confused about two things the dive shop owner was telling me.

1. He said with his Nitrox fill system I could use my regulator and my tanks and switch back and forth between air and nitrox because of the way he injected oxygen into his fill system. Others have told me that if I fill Nitrox then go back to air I need to have the tank valves rebuilt/cleaned? Also this operator said The regulator doesn’t matter who fills my tank it can be used with air / nitrox and back and forth without cleaning and/or rebuild. If that’s true then why rebuild the tank valve? Also if that’s true then why does Apex sell a nitrox regulator that can be used with an up to 40% ox enriched mix?

2. My second question is most perplexing. This dive shop said I should by his Faber LP tank because he always fills them to 4000 psi then lets them cool to 3700psi nitrox or not. I thought the Faber LP was max to 2450 with a 10% overfill. Wouldn’t’ that be 2690psi? When I questioned him he said the tanks could take it and they held more air because the walls of the tank were thinner.

3. Last I’m looking to switch form yolk to DIN but with all this different info now I’m looking to not repair my present gear (yolk, air only), and not go diving until I get all these issues worked out then by new gear.

What’s up? Air, Nitrox, HP, LP, DIN, Yolk?

Thanks in advance for any help.

 

[Tamas]

#1. you can use your "unclean" tanks if he uses a premix or a continuous blend, but if he uses partial pressure blending (which means first filling the tanks with pure O2 then topping it off with air) then you need to get them cleaned.
#1a. if you fill your tanks with plain ole' air then you need to get them cleaned again if you wish to have them filled by partial pressure blending again, the other solution is to use hyper air which has already been filtered, removing most of the contaminants. (shops that fill nitrox with the PP method have this)

#2. while most tanks in NA are the same as the ones used in Europe but rated a lot lower fill pressure, they can take the pressure (theoretically here - no war) but most shops will not fill past their fill rating. However in cave country they often over fill tanks but you have to have the burst disk for it the equipment and frequently test the tanks to keep it safe. Again in theory the tanks can take pressure up to 5000psi (since that is where they are tested/certified at) it is not something you want to do on a regular basis. Do you really want to be diving with little missiles on your back?

#3 switching your reg from yoke to din is a no biggie, if you are going to use higher pressure tanks then you might as well and then just use the din-to-yoke adapter on tanks that do not have a din fitting

 

[pants!]

I'm new to this forum and Nitrox. I am going to sign up for Nitrox training in a few weeks. I've been diving since the early '80s and I've logged well over 600 dives. So I would not say I'm an expert by any means but when something dosen't sound right I've gotta ask some questions.

The set of tanks I'm using now are in for another hydro(third I think). I was in a local dive shop last night and I’m looking for a new set of tanks and a new regulator. I am confused about two things the dive shop owner was telling me.

1. He said with his Nitrox fill system I could use my regulator and my tanks and switch back and forth between air and nitrox because of the way he injected oxygen into his fill system. Others have told me that if I fill Nitrox then go back to air I need to have the tank valves rebuilt/cleaned? Also this operator said The regulator doesn’t matter who fills my tank it can be used with air / nitrox and back and forth without cleaning and/or rebuild. If that’s true then why rebuild the tank valve? Also if that’s true then why does Apex sell a nitrox regulator that can be used with an up to 40% ox enriched mix?

2. My second question is most perplexing. This dive shop said I should by his Faber LP tank because he always fills them to 4000 psi then lets them cool to 3700psi nitrox or not. I thought the Faber LP was max to 2450 with a 10% overfill. Wouldn’t’ that be 2690psi? When I questioned him he said the tanks could take it and they held more air because the walls of the tank were thinner.

3. Last I’m looking to switch form yolk to DIN but with all this different info now I’m looking to not repair my present gear (yolk, air only), and not go diving until I get all these issues worked out then by new gear.

What’s up? Air, Nitrox, HP, LP, DIN, Yolk?

Thanks in advance for any help.

1) You can use any regulator at all when using standard recreational nitrox mixes. The confusing part is with the tank. The *short* version is that any tank that is going to have PURE O2 pumped into it needs to be O2 clean, and filling with "regular" air makes a tank not O2 clean. One method of Nitrox filling is to add pure O2 to an empty tank and top it off with air.. this method requires O2 clean tanks. Another method is for the dive shop to have high pressure banks of pre-made nitrox. Using this method, your tank only gets filled from the pre-mixed nitrox and never sees pure O2, so this type of nitrox can be used in any tank.

2) Faber LP is 2400 + 10% overfill (if still in + hydro) for 2650 psi service pressure. Some people will pump steel LP tanks way above service pressure because they feel the tanks can take it. The only data to support this is that it's commonly done in certain parts of the country and, to my knowledge, has never resulted in a catastrophic failure of a steel tank. However, I have heard anecdotal evidence that these tanks very often fail their first hydro. Only a complete moron with a death wish would ever do this to an aluminum tank, so you never see that happening.

3) Just FYI, it's yoke not yolk. I like DIN better, but DIN tank valves are less common.

 

[pants!]

#2. while most tanks in NA are the same as the ones used in Europe but rated a lot lower fill pressure, they can take the pressure (theoretically here - no war) but most shops will not fill past their fill rating. However in cave country they often over fill tanks but you have to have the burst disk for it the equipment and frequently test the tanks to keep it safe. Again in theory the tanks can take pressure up to 5000psi (since that is where they are tested/certified at) it is not something you want to do on a regular basis. Do you really want to be diving with little missiles on your back?

There are lots of debates about this in the archives here on SB, but there are a couple of lessons I've taken away by reading them.

#1: The Faber LP tanks in NA do NOT have the same physical characteristics as the ones sold in Europe.

#2: Hydrostatic testing is very time limited and in controlled conditions. Filling a tank with 5000 psi of water for a minute or two in a lab is a very different thing from filling it with 5000 psi of much higher-energy air, letting the fill sit for days or weeks, and in that state letting it heat, get tossed around, etc etc.

 

[Tamas]

There are lots of debates about this in the archives here on SB, but there are a couple of lessons I've taken away by reading them.

#1: The Faber LP tanks in NA do NOT have the same physical characteristics as the ones sold in Europe.

#2: Hydrostatic testing is very time limited and in controlled conditions. Filling a tank with 5000 psi of water for a minute or two in a lab is a very different thing from filling it with 5000 psi of much higher-energy air, letting the fill sit for days or weeks, and in that state letting it heat, get tossed around, etc etc.

I realize that, hence the "theory" part. But it seems that some people will fill their tanks to 4000psi and dive them on a regular basis with no ill affects.
And if I remember correctly, for NA there is rule to have everything rated with a 50% safety margin to allow for such events. (not that one should bank on it)