How often do you actually get a full tank fill?

[Still Kicking]

I tell coworkers ... no quicker way to piss off a customer than to give them a short fill. It costs nothing extra in practical terms to fill a tank to working pressure. Basic customer service.

I tell customers .... your tank is full but will cool down. If you're not in a rush, look around the shop and I will top it off to working pressure.

As for rentals i check them but the renter is also responsible for checking the proper function of the gear they rent including a full fill and signs paperwork that they are happy with it.

As for dropping a whip in the water bath .... put a leash on it so it can't reach the water (also for safety if a fitting blows).

 

[lexvil]

I generally consider anything under 3500 a short fill, find a shop that will do it right and get to know the people working there, I get quick water bath fills to 3700/3800 all of the time by filling near the dive sites, the valley fills take 2 days to get a 3400 fill so I just don’t go there.

 

[Belzelbub]

At the local shop I use most often, I have never gotten a short fill. Over 3600 is the norm. Occasionally it will be in the 3800 range. I usually fill with EAN, so before I leave, or even pay, one of the employees will check pressure and mix with me witnessing. I think in one instance it might have been a little short at that check. The employee noticed and took it back to top off. I didn't even have to ask. In that case, the issue was actually due to a valve that was leaking slightly. They took care of that and filled my tank.

 

[Johnoly]

What I really like is ...Gas is different than liquid. So if you fill a clear container up with water and it overflows, you can say it's full and more won't fit inside.

But gas is great because even at just a few psi it over flows out the opening. But unlike water, you can keep stuffing in more and more and more gas so it's never really full. {kinda lol }

 

[Arkman]

This is a constant struggle for me and my buddy at my local shop. We don't really have an option for another shop, there is only one. I try dropping my tank off and leaving it for a while, but that doesn't seem to help.

I have HP 100's that are rated to 3500 (Older PST tanks). They put a sticker on there that says fill to 3442. I don't care about the 48 psi, but it is weird that they didn't notice that they are actually rated to 3500. Werid.

It has been common for me to get a 2800 to 2900 fill. Which, in a set of HP100 doubles, that's a lot of gas I'm missing. For my typical diving, that is probably 30 to 40 minutes worth of gas.

My buddy has LP85s with the + stamp and one of the last times they filled they told him the plus stamp brings it up to the stamped pressure. Not 10% beyond that. And the plus is only good for the first hydro, so would only give him a 2,200 fill, rather than a 2,640 fill. Even though they were the ones that got the + put on the tank at the last hydro. That was a part time fill guy, not the owner...

We've had better luck lately after having the conversation that we need FULL fills. But only if the owner is there, the others just dont do it. They hot fill to the rated pressure (or so) and then let them cool, they don't top them off.

Does have a guess what a set of double HP 100's rated to 3,500 would need to be hot filled to, in order to cool to 3500? I know it kinda depends on temps and stuff, but just roughly.

 

[inquis]

Does have a guess what a set of double HP 100's rated to 3,500 would need to be hot filled to, in order to cool to 3500? I know it kinda depends on temps and stuff, but just roughly.

Ballpark 3700-3750 psi. That allows for a 100-110°F tank cooling to 3500 at 70°F. The two big contributors are how fast is the fill and how empty it was to start.

 

[Divin'Papaw]

Does have a guess what a set of double HP 100's rated to 3,500 would need to be hot filled to, in order to cool to 3500? I know it kinda depends on temps and stuff, but just roughly.

Without running the calculation, easily 3750-3800 range I believe.

 

[GiraffeMarineSalvage]

Short fills can be frustrating but what I get most anxious about is getting moisture in my steel tanks if a shop (especially in humid warm locations..) almost only ever fills aluminum tanks because the air may not be as dry as it should be.
I've never run a dive shop or gone over a small dive shop's financials but in general I view almost every small dive shop filling tanks themselves (as opposed to scaled up to support multiple dive shops) as generously providing a service that more likely than not is subsidized by the rest of their business if one takes into account all the costs of labor, compressor maintenance (both consumables and longer term) and electricity. So for a full fill of my steel 120s I am both picky on where they are filled and like others have said I give them time to have topped off when their compressor has to normally run.

 

[macado]

I was not going to weigh in here as I have my own compressor so it's been a while since I have gotten a short fill and if I do I can only blame myself however It's really not too complicated.

I say that as somebody that used to occasionally fill tanks at a dive shop when I was bored (It was not my primary job function but if I was teaching a class and the owner/shop staff was busy I would fill tanks for people). The deciding factor usually depends what pressure the banks are at if you're not filling directly off the compressor. If banks are over ~4000psi then it's pretty easy to ensure a good fill. Obviously this is a very simplistic overview as it depends on the size/volume of the banks and how many tanks I have to fill. The shop kept their high pressure bank at 4500psi. If your shop is keeping their banks at 3500-4000psi then you might struggle to get consistently good fills.

Pressure₁ / Temp₁ = Pressure₂ / Temp₂

Some very basic math following ideal gas laws (not accounting for z-factors or gauge pressures).
Let's assume your tanks are "hot filled" to ~3900psi at 120f and we want them to cool down to room temperature (70f)

Pressure₂ = Pressure₁ x (Temp1 / Temp2)

Temp₁ = 120°f → 322.03 kelvin
Temp₂ = 70°f → 294.26 kelvin

Pressure₂ = 3900psi x 294.26 / 322.03 = 3563 psi
You're looking at ~337psi drop but let's round up to 350psi-400psi for extra posterity. If I messed up the math feel free to correct me. I wont be insulted. I didn't factor in z compressibility or absolute pressure but it's accurate enough.

TL;DR - Fill tanks to 3900-4000psi. They will cool down to ~3500psi. No fancy math required and your customers will be happy. If someone complains about a 200psi "over fill" well I'm happy to drain some gas out but nobody ever took me up on that offer.

 

[fred32176]

My LDS usually fills my steel 100s to 3400 psi and the tank is room temperature when I pick it up. I have had a tank filled only to 3200 psi but I stopped by the shop while the tank was hot and I didn't want to wait for it to cool and be topped off.

Tanks provided by dive operators are often AL80s filled to 3000 lbs.