Air Fill Protocol

[dfx]

That one has been debunked according to this: http://www.fillexpress.com/library/dryfills.pdf
Basically it states that the tank doesn't sit in the water long enough for it to have an impact on the temperature inside the tank.

TLDR :tongue2:

Seriously though. All else being equal, a tank filled while sitting in a water bath will end up with more air in it than one which wasn't. We all know that water conducts heat much better than air, so the water will always absorb more of the generated heat than air. The difference might not be a whole let (esp for AL tanks, which is a good point, as AL doesn't conduct heat as well as steel), but at least it's something.

Why do some LDS not understand It's not an over fill or overfilling a tank if when the tank cools to 72F it's at the rated pressure?

Argh, but it is. That's what has been explained in great detail already. It's not an overfill with regards to amount of contained gas, but that doesn't matter. Tanks are rated and tested for a certain pressure, not amount of gas. If you exceed that pressure at any point (even if it's caused by raised temperature) then yes, it's too much, even though the hydro tests etc are done for a much higher pressure. That's just your safety margin and you shouldn't rely on that.

 

[Mitchell Teeters]

I'm dealing with a local diver doing fills, he refuses to fill to allow for cooling. I'm going to have to have a conversation with him. Let's face it, less air in the tank means more fills for the LDS. It isn't just about safety.

When I was working at the quarry as a tank monkey we filled 10% over to allow for cooling.

 

[jmneill]

This thread reminds me of how happy I was a few years ago frequenting Ginnie springs. I never walked away with a fill under 3200. Makes you feel good even though you come back with half of it.

 

[windapp]

Argh, but it is. That's what has been explained in great detail already. It's not an overfill with regards to amount of contained gas, but that doesn't matter. Tanks are rated and tested for a certain pressure, not amount of gas. If you exceed that pressure at any point (even if it's caused by raised temperature) then yes, it's too much, even though the hydro tests etc are done for a much higher pressure. That's just your safety margin and you shouldn't rely on that.

Not really

I tank that is rated for 110F at full pressure will go from 3000 PSI at 72 F to 3214 PSI at 110F. The maximum rated pressure for the tank under all temperatures would be 3214 PSI before safety factor, so if you filled a tank, and it settled to 3000 PSI at 72 F and never exceed 3214 PSI during the fill, you have not exceed the maximum pressure. Furthermore, if you filled it to 3214 PSI at 72 F, and never exceed 72 F, you still won't have exceed the rated pressure.

 

[leabre]

Not really

I tank that is rated for 110F at full pressure will go from 3000 PSI at 72 F to 3214 PSI at 110F. The maximum rated pressure for the tank under all temperatures would be 3214 PSI before safety factor, so if you filled a tank, and it settled to 3000 PSI at 72 F and never exceed 3214 PSI during the fill, you have not exceed the maximum pressure. Furthermore, if you filled it to 3214 PSI at 72 F, and never exceed 72 F, you still won't have exceed the rated pressure.

Do tanks have maximum temperature ratings specified by the manufacture in the sense that you just described? (besides AL at 300* F but that's a heat stress issue on the alloy)?

[Edit] Would this be the maximum working pressure MWP?

 

[macado]

TLDR


Argh, but it is. That's what has been explained in great detail already. It's not an overfill with regards to amount of contained gas, but that doesn't matter. Tanks are rated and tested for a certain pressure, not amount of gas. If you exceed that pressure at any point (even if it's caused by raised temperature) then yes, it's too much, even though the hydro tests etc are done for a much higher pressure. That's just your safety margin and you shouldn't rely on that.

This is not necessarily true. Cylinders can be filled to a certain pressures based on temperature they're at during the fill process. A slight overfill is allowed I believe as long as tank does not exceed 130f. A cylinder is considered at full service pressure when it's at 70f.

This has been discussed at length here by several other people. Someone more knowledgable on CGA regulations can probably explain it much better than me but I believe CFR 173,301a(c) states this. This was referenced in a previous thread.

See this thread..
http://www.scubaboard.com/forums/tanks-valves-bands/153040-why-wont-my-shop-give-me-10-overfill.html

 

[windapp]

My tanks have a temperature rating full, and one at low pressure (presumably for the heat stress issue).

 

[D_B]

TLDR :tongue2:

Why do some LDS not understand It's not an over fill or overfilling a tank if when the tank cools to 72F it's at the rated pressure?

Argh, but it is. That's what has been explained in great detail already. It's not an overfill with regards to amount of contained gas, but that doesn't matter. Tanks are rated and tested for a certain pressure, not amount of gas. If you exceed that pressure at any point (even if it's caused by raised temperature) then yes, it's too much, even though the hydro tests etc are done for a much higher pressure. That's just your safety margin and you shouldn't rely on that.

Then I take it that you let air out of your tank to get it down to a safe 3000 PSI when/if it warms to 85 during the day?

I'm going to have to disagree with your premise that my tank is overpressure if I dont do that

 

[chrpai]

I'm not a tank monkey, but from whatI've read an AL80 properly filled to 3000psi at 70f will raise to 3342 psi at 130f. This is quiet acceptable.

Here's some really good reading material on the subject:

http://www.fillexpress.com/library/dryfills.pdf

 

[dfx]

Then I take it that you let air out of your tank to get it down to a safe 3000 PSI when/if it warms to 85 during the day?

I'm going to have to disagree with your premise that my tank is overpressure if I dont do that

There's nothing to disagree about, overpressure is overpressure. Those are hard facts. If a tank is rated to 3000 psi and you let it go above 3000 psi, then it's too much pressure. It doesn't matter if this is caused by too much gas or by too high temperature.

The only thing to disagree about is how much overpressure is acceptable. If you see 3500 psi as acceptable pressure for a tank that's rated to 3000 psi, then so be it. But again it doesn't matter if this pressure is caused by an overfill (too much gas) or by an increased temperature (with the same amount of gas) or maybe by a combination of the two. It's always pressure that matters and nothing else.

In other words: If you think a tank filled to 3000 psi at room temperature is ok to heat up to a temperature where it will read 3500 psi, then by deduction you also need to be ok with a tank at room temperature that's been filled to 3500 psi, as long as you don't expose it to heat.