Question regarding tank fills

[CaptainPanda]

Hi, all, as the title suggests, I have a question regarding the tank fills at my LDS. I have a steel 100 tank that I use all but exclusively.

As far as I understand, the shop does a sort of quick fill method; they overpressurize the tank, and then cool the tank in water so that, when cool, it should be at the rated pressure of the tank, either 3000 for their 80s, or 3442 for my 100.

I've never had it filled to 3442 psi; I think the closest I ever came was 3000. I had a yearly visual done on the tank a few weeks ago, and when the tank was filled afterward, my SPG showed a pressure of 2500. I felt a little ripped off, but I didn't mention it to the LDS because it had been a couple of weeks since the fill that I went diving, and I'm not really sure I understand enough about the fill process to make an educated complaint.

This afternoon, I got another fill at the LDS for a dive planned for tomorrow. I just put the SPG on the tank, and it's showing a pressure of 2200. Am I right in thinking that something's wrong in this situation? I get it that pressure drops as the air cools, but it shouldn't drop that much, right? Am I missing something?

(I do plan on asking them if I can use one of their full tanks to check and make sure that it's not my SPG, but I thought I'd start here in the meantime)

 

[SaltyFrog]

If your spg is working fine, and your valve doesn't leak, then this much of a difference is considered a short fill and they should top you off.


Although the industry standard, so to speak, is for you to check the tank yourself to make sure it has the fill that you want afterwards. And ask LDS to top off if it's short.

I've had my fair share of short fills with shops that I always double check after fill.
Shops are more than willing to lend me their spg if for whatever reason I don't have mine.
And they are always willing to top off if short.

For hot fill method, or whenever the tank is hand warm, it should have max+100~200 psi, so that when in cold water it gets to max psi.

 

[Brett Hatch]

Hi, welcome to Scuba Board.

Some common dive shop compressors aren't really able to push gas higher than 3000 PSI. If theirs is like this, they simply will never be able to completely fill that tank. If you have never had a good fill from them, then you might ask if their compressor can do it. A steel HP100 filled to 3k contains 3000 / 3442 * 100 = 87 cu ft of gas. Which ain't the end of the world, but you might consider selling or trading it for a low-pressure steel tank if that's the only local option for fills. 2200 is ridiculously low though, there's not much excuse for that.

(I do plan on asking them if I can use one of their full tanks to check and make sure that it's not my SPG, but I thought I'd start here in the meantime)

It's worth checking the SPG out, since it could be faulty. But if your SPG is all good and the LDS does have a high-pressure compressor capable of doing 3442, then it's more of a cultural problem. Agree with @boboqa 's advice to check the pressure before you leave every time, and if it's below 3442, ask for a top-off. If they give you any guff about it, then the hell with them, find another shop.

That's my 2 psi anyway, your mileage may vary.

 

[Marie13]

When I used to have HP tanks some shops in the Chicago area were unwilling or unable to fill them to service pressure. They were only interested in filling AL80s. I went elsewhere.

 

[Divin'Papaw]

Sounds like a classic short fill. It's all too common in the Midwest. Your situation though sounds completely unacceptable. I used to regularly get 3200-3300 fills in my HP100s, but 2200-2500 is ridiculous. I'd suggest you buy an inexpensive pressure checker and test your tanks before you leave with them. If they're too low point it out and politely but firmly ask that they be topped off.

 

[CT-Rich]

What you are getting is a hot fill. They pump it up over the target pressure and hand it back to you. When it cools off (compression of air creates heat) the tank should be close to its rated pressure. It Doesn’t usually work that way and you get a short fill.

Two suggestions:
First, leave the tank over night. The can fill it, let it cool off and top it off properly at its rated pressure.
Second, check the tank at the shop. If it not completely full, ask them to top it off for you.

As has been pointed out, the shop may not be able to properly fill the tank, then it is time to find another shop. Tank fills drive all other sales, because that weekly visit gives you a chance to shop for other items, expecting a proper fill is good business for the shop.

 

[ajtoady]

I am very forntunate to have unlimited access to a Bauer system capable of 5000 psi. I slow fill my HP tanks to around 3600 and usually end up at 3400 or so. Hot fills will short your fill considerably but, 2200, is a bit extreme. My thoughts are, if they are shorting you, they are aware of it and should be called out.

 

[Divin'Papaw]

The only way to get a quick (hot) fill in a HP tank is to significantly overfill it (3800-4000) or use a cold water bath.

As mentioned the other option is to leave it and have them fill it and then top it off after it’s cooled.

One of the shops I use regularly in FL has a cold water bath the tanks are filled in plus they fill them to 3700-3800. In about 10 minutes I’ve got an ice cold tank with 3500-3600 psi. They never short fill me. My starting pressure on the boat is always in the 3500-3650 range.

A second shop I use keeps them overnight. They fill them, let them cool and then top them. When I pick them up they always have between 3450-3600. Again, a good solid fill.

Two ways to skin the cat.

 

[rob.mwpropane]

I would think that the statement made by @CT-Rich; "tank fills drive all other sales" would be a pretty good indicator of how the rest of the shop is ran. If they can't or aren't willing to fill a tank to it's capacity (without saying anything in advance) then they probably aren't giving great service in other areas. 2200 in a 3442 is appalling, shameful really.

The best shops in my area hot fill 3442's to ~ 3900 from a bank. They fill slower (5-6 min) and I'm usually left with 3400 or so when cooled.

There's always the 3rd option, buy your own compressor I'll praise mine right up until she breaks, then I'm sure I'll be on here crying about it!!

 

[Barnaby'sDad]

I am very forntunate to have unlimited access to a Bauer system capable of 5000 psi. I slow fill my HP tanks to around 3600 and usually end up at 3400 or so. Hot fills will short your fill considerably but, 2200, is a bit extreme. My thoughts are, if they are shorting you, they are aware of it and should be called out.

This. If they’re shorting you by that much, they’re aware of what they’re doing. Find another shop to fill, if possible.

Just getting tanks filled can be a major hassle in some places. In particular for HP tanks at shops that mostly fill AL80’s. One place I used I think is just too lazy to run their booster system. ~3,000 psi fills “on the reg” even for fills that aren’t hot.