how do you get hot fills from air bank?

[EastEndDiver]

It all has to do with phycis................ errr phycsis...........eerr pyhsics..........eerr pyshics...........eerr...........phcyhics............does anyone know how to spell physics?

 

[DA Aquamaster]

Unless you overfill your tank, there is no way to get a quick, fill-while-you-wait full fill. Unless perhaps someone has a cryogenic fill station.

Technically the tank is correctly filled if it ends up having the rated pressure in it when everything stabilizes at about 70 degrees.

So... when I take a 2250 psi steel tank and "hot" fill it to 2600 psi, it is still legally filled as long as it cools to no more than 2250 psi at room temp.

It is no more "overfilled" than it would be if I filled it very slowly and carefully to 2250 psi at room temp and then put it in my trunk or left it out in the sun on a sunny 105 degree day.

The tank would however be overfilled if I filled it very slowly and carefully to exactly 2250 psi at the shop's outside fill station on a nice January morning with an air temp of 20 below zero as the pressure would then be well over 2250 psi. when it warmed to room temperature.

The service pressure and capacity are defined at room temp. Consequently, if I filled the tank to exactly 2250 psi at room temp, it would still hold exactly the same volume of gas regardless of whether the filled tank subsequently gets heated or cooled above or below room temperature.

Obviously, you need to use some moderation here as filling the tank in 30 seconds would produce a lot of heat and the ending pressure needed to produce a good fill when things stabilize at room temp would be excessive and not in the best interests of the tank or the person doing the fill.

The problem that you encounter in many shops though is the misunderstanding that it is only legal to fill a tank if you do not exceed the rated pressure of the tank at any point. In practice that means the shop monkey stops the fill on the now warm tank when it reaches it's service pressure which under all but the slowest fill rates guarentees the tank is going to be 100 psi, 200 psi or more underfilled when the tank cools to room temp.

 

[SparticleBrane]

...I once filled a 13cf pony bottle to ~2000psi with 40% in say...about 1 second?
Not the smartest thing I've ever done!

Guy had a set of 120cf dolphins. There were a few other things going on in the shop and I wasn't paying attention and forgot about the tanks being filled. They had ~2200psi of 40% in there, if I recall correctly. That was a few hundred too much, but he wanted his 13cf pony filled up too.
Figured I'd fill up the pony from the dolphin...cranked that sucker wide open. Like I said, not the smartest thing I've ever done.

 

[cummings66]

who said anything about being rude? my complaint was that i wasn't getting the fill that i paid for. i guess it's not ok to ask for the last 10-20% of

I agree you aren't getting a full fill and that you're paying for one. I'd go one step further and say the guy has little training in filling tanks either. In our Nitrox class they told us to ask for the paperwork proving they took the classes to qualify them for filling tanks, and other things to boot. It was a Padi class so they mentioned the DSAT classes by name as one to ask if they did. My LDS gives me full fills and the people that fill the tanks have training from the shop only, but they're pretty thorough.

As I read your initial post it came across to me that you knew more than the guy filling the tank and you informed him of such by telling him he was wrong that you can't get a hot fill from banked tanks and so he should have been able to fill your tank full.

If I did what you said you did in the first posting I'd apologize if for no other reason than to admit my error and generate good will with that shop. If I'm wrong I will admit it and apologize, but that's me.

 

[SparticleBrane]

Yes most people don't have a huge amount of training. My post above probably makes it sound like that, but to my defense it was 10:30pm when I was filling those tanks.
Whenever I fill tanks (except for that once, heh) I do it as slow as I can get away with. Obviously the second morning of my rescue class when we had ~15 people who needed 2 fills each, in a filling station that fills 2 tanks at a time, they're going to get filled quickly. However, that situation hopefully doesn't come up too often.
I think that as long as someone has a reasonable understanding of what's going on and can read the markings on the tanks, then they should be able to fill basic air tanks. I don't personally see the need for a "class" when it's just as easy to have someone train you in the shop on the first day and watch over you for a few afterwards to make sure you're doing it correctly.
Nitrox and Trimix, however, are another ballgame.

 

[Luis H]

Technically the tank is correctly filled if it ends up having the rated pressure in it when everything stabilizes at about 70 degrees.

So... when I take a 2250 psi steel tank and "hot" fill it to 2600 psi, it is still legally filled as long as it cools to no more than 2250 psi at room temp.

It is no more "overfilled" than it would be if I filled it very slowly and carefully to 2250 psi at room temp and then put it in my trunk or left it out in the sun on a sunny 105 degree day.

The tank would however be overfilled if I filled it very slowly and carefully to exactly 2250 psi at the shop's outside fill station on a nice January morning with an air temp of 20 below zero as the pressure would then be well over 2250 psi. when it warmed to room temperature.

The service pressure and capacity are defined at room temp. Consequently, if I filled the tank to exactly 2250 psi at room temp, it would still hold exactly the same volume of gas regardless of whether the filled tank subsequently gets heated or cooled above or below room temperature.

Obviously, you need to use some moderation here as filling the tank in 30 seconds would produce a lot of heat and the ending pressure needed to produce a good fill when things stabilize at room temp would be excessive and not in the best interests of the tank or the person doing the fill.

The problem that you encounter in many shops though is the misunderstanding that it is only legal to fill a tank if you do not exceed the rated pressure of the tank at any point. In practice that means the shop monkey stops the fill on the now warm tank when it reaches it's service pressure which under all but the slowest fill rates guarentees the tank is going to be 100 psi, 200 psi or more underfilled when the tank cools to room temp.

You are correct, but there is another limit. The codes also only allows a maximum temperature of 130 F for compressed gas cylinders. That means that the 2250 PSI tank at 70 F when it is at 130 F can only have 2506 PSI.

That being said, a 2250 PSI tank should probably have a new + if it was properly tested and the proper criteria’s where met. Therefore that would again be a 2475 PSI tank (and at 130 F it could have 2755 PSI).

Personally I can’t remember seeing this in CFR 49 (Code of Federal Regulations 49, the applicable DOT compressed gas cylinders code), but the code refers you to CGA documents (Compressed Gas Association) for some of this details.