How often do you actually get a full tank fill?

[Moby Dickins]

As the proud new owner of a beautiful 100 HP steel tank I'm looking back on my rental days, and just about never was it filled to spec. Of course, once in the cold water the psi would droop ever lower.

For more experienced tank owners, how often does your tank actually get filled to spec? With adiabatic heating during the fill process the internal PSI will only drop as it reaches ambient temperature.

Is the rule of thumb to buy a 100 when you need 90 cubic feet, and a 120 when you need 100?

 

[DOBY]

Two option are available to help with getting a “full fill.” The tank can be filled in a water bath to help keep it cool during filling, or the tank can be filled to working pressure and then topped off back to working after it cools.

Overfilling so it drops to working pressure once it cools is not a recommended option.

 

[Divin'Papaw]

As the proud new owner of a beautiful 100 HP steel tank I'm looking back on my rental days, and just about never was it filled to spec. Of course, once in the cold water the psi would droop ever lower.

For more experienced tank owners, how often does your tank actually get filled to spec? With adiabatic heating during the fill process the internal PSI will only drop as it reaches ambient temperature.

Is the rule of thumb to buy a 100 when you need 90 cubic feet, and a 120 when you need 100?

I get a solid HP 100 fill almost 100% of the time. I only use high volume, reputable shops in South Florida which is where I do all of my diving. It is EXTREMELY rare to get a short-fill. Actually, I don't recall the last time it happened. Rather, I typically have 3550-3800 after the tanks have cooled fully.

 

[johndiver999]

You need to have serious talk with the shop and get a confirmation of what their attitude is.

At the one I go to, they pretty much always slam them up to 3800 and they have a water bath to keep them somewhat cool. I have more problems with them filling the 2400 psi tanks to 3000, but about every 5-th time, they accidentally fill my LP to 3800. I don't expect a great level of competence from the people who actually fill tanks.

 

[Divin'Papaw]

You need to have serious talk with the shop and get a confirmation of what their attitude is.

At the one I go to, they pretty much always slam them up to 3800 and they have a water bath to keep them somewhat cool. I have more problems with them filling the 2400 psi tanks to 3000, but about every 5-th time, they accidentally fill my LP to 3800. I don't expect a great level of competence from the people who actually fill tanks.

I think we use the same primary shop

 

[Moby Dickins]

You need to have serious talk with the shop and get a confirmation of what their attitude is.

Just to clairify, short fills are not my experience with any local shops, because I don't have enough experience with local shops. This is based on my experience as a vacation rental person who never saw an HP tank above 2800 psi. I posed the question because I'm curious how it translates to filling at the local dive shop.

 

[Scuba_Jenny]

The place I've been going to for the past couple years mostly fill my tanks to the correct pressure. Because I check my tanks every time, they have learned that a "happy fill" = they don't have to take the tank back for a topper. Too many times in the beginning of me going there, the tanks were slightly under pressure. I'll attribute it to previous employees were clueless. Some still are, and they get to lug the tanks back and do the job correctly..

 

[jborg]

Overfilling so it drops to working pressure once it cools is not a recommended option.

Why not? AFAIK the standards explicitly allow for this; the working pressure is defined for a standard temperature (~20 ℃), and there is a separate maximum temperature the tank is allowed to experience. I'm pretty sure that temperature is higher than the output of most compressors, often ~70 ℃.

 

[sea_ledford]

Two option are available to help with getting a “full fill.” The tank can be filled in a water bath to help keep it cool during filling, or the tank can be filled to working pressure and then topped off back to working after it cools.

Overfilling so it drops to working pressure once it cools is not a recommended option.

Wet fills are no longer recommended. Too many dropped fill whips into the water and straight onto your tank, which introduces water. Plus it is hell on the tank fillers back.

It isn't over filled if it is at correct pressure once it is at room temp.

What is probably happening with OPs tanks is they are getting filled with other AL80s, so only filled to 3000, maybe 3200 warm. But because they are steel, they heat up faster during filling (thinner tank walls), so they are lower than the AL tanks they are filled with. That might be because the fill station is regulated to 3200 psi, or it might be done manually by the filler. Either way, make sure you tell them that you have HP tanks and the fill pressure is 3500(ish). They'll tell you if they can fill that high or not.

 

[Divin'Papaw]

All sorts of recommended/not recommended options listed above that contradict each other. Everyone seems to have an opinion when it comes to tank filling procedures. It seems to have the most widely varied "recommended best practices" than about any other part of the dive industry.

The one shop in South Florida that uses a water bath that I am aware of is a VERY high-volume shop for fills, especially on weekends and over holidays. Not using a water bath would slow their turn around significantly. I use them all the time and have never had a wet fill. My HP steel tanks pass VIP and hydro consistently and I've been using them for over 7 years now. In the entire time I've been in South Florida (9 years now), I've never had a HP steel fail VIP, hydro, or require a tumbling or whipping.