How often do you actually get a full tank fill?

[Scott G. Bonser]

What gear was designed for 2250? Sure there were some 1800 psi co2 bottles converted for scuba use back in the early early days, but I don't know of any commercial gear made for that.
Most of the early scuba tanks were 2475 psi and gear was designed for the tank pressure available at the time.

You can fill to whatever pressure make you happy, but I don't think your gear design is the limiting factor.

Good observation. I have gotten fills up to 2500psi and felt confidant that that pressure wouldn’t wear down my vintage gear. Before I knew better I got fills to around 3000 and had no trouble but my USD Royal Aquamaater was made in either ‘71 or ‘72 ( one of the last few years they were made ) and had no indication of excessive wear. It was later found out from numerous sources that if you were diving double-hose regulators that tanks should only get filled to 2250psi for best performance and less wear and tear. I am no expert but overwhelming advice regarding my tank fills are taken into consideration as parts for some of my vintage equipment is difficult if not impossible to find. When diving my single-hose regulators, I have gotten fills to 3500+/- psi w/no issues. I have never tried out ‘converted’ industrial gas tanks as I am leery of residues and reactiveness even if tanks have been cleaned and evaluated for contamination. Thanks for your input and ‘Good Diving’ to you

 

[sena_akutsa]

all cylinders we have in our Club are steel, rated 235 bar (3400 psi)
To stay on safe side, our neighbor (shipyard owner) set the shut switch to 210 - 220 b

Fortunately, the employee who fills has time to top-up as we dive on Saturdays.
Starting with 200 bar (3000 psi), the only choice we have is the volume: 12L, and 15L;
we all cope with that, as our nowaday's priority is to get a second Zodiac and more Regs.

 

[halocline]

With regards to the water bath, I wonder if some of the people posting on this appreciate that it is the air temperature, not the tank wall temperature, that determines the pressure at a given volume. The water bath won’t keep the air from heating up, but it will help it cool faster because the tank will absorb more heat from the air if it’s in a cold bath. AL tanks generally have much thicker walls, but AL is a more efficient conductor of heat than steel, so in terms of which type of tank cools faster, I don’t really know. What I do know is that even if the tank is kept cold in water during the fill, and then removed right away when it’s filled, it will still heat up. So I doubt that filling in a water bath makes that much difference, unless the tank continues to sit in the water for some time after the fill is complete.

 

[Johnoly]

not the tank wall temperature, that determines the pressure at a given volume.

In your great post you've listed most of the dozen or so variables that fillers encounter. Probably the worst is the loaded up pickup truck filled with tanks that BAKED in the hot noon 90 degree sun while they sat for lunch. Then wanted all those tanks filled for an afternoon dive and screamed at the dive site because they cooled to 2900.

Most shops will store tanks for later pickup so the diver doesn't have to wait while filling. Our SE Fla high fills shops are doing 150-250 tanks per day in 8 whips ice baths. The chilled/ice bath is normally used in many of these high volume fill stations and they don't store diver's tanks, the customer waits & takes. I rarely see an ice bath at a normal LDS. Depending on the dozen heat variables the ice bath lets them gain enough psi thru heat reduction transfer &, total fill time to get an cooled EAN AL80 @3200 in just under 8 minutes. (ohh yaa>>how dare you ask for a different mix from the 36 bank on a summer holiday weekend with a line of tanks out the door, lol! )

 

[CT-Rich]

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 drop my tanks off to be filled at the shop and pick them up a day or two later. I put them on the shop gauge when they come out (before they are paid for). If they are light, I ask them to top them off. You don't have that happen many time for them to realize life is easier if they give me a proper fill from the start. I am never rude and if they say the bank is low, I accept it with a smile. I very seldom have issues with how good my fills are. They know my expectation and I don't give them a reason to dislike me.