How Cave Shops Calculate Cubic Feet

[Tracy]

Pray tell which shop?

I have no knowledge where he went, but it sounds very DO.

 

[Tracy]

Maybe it's just me and I'm missing something..... but if I bring in a tank with existing 300psi or a tank with existing 1500psi..... then they charge the same price to fill the tank to full working pressure.

Generally, technical shops charge by the cubic foot. You pay for the gas you get.
It helps promote safer reserve gas usage as there is never a reason to drain a tank down. You don't save any money by cutting out your reserves.

 

[boulderjohn]

Maybe it's just me and I'm missing something..... but if I bring in a tank with existing 300psi or a tank with existing 1500psi..... then they charge the same price to fill the tank to full working pressure.

In cave country they charge by the cubic foot. Which allows to differences in tank sizes and starting pressures. So my LP108s cost more to fill than my LP85s.

As Manatee Diver said, there is a big difference in procedure in cave country because there is a big difference in volumes. Let's say you are diving to thirds in a cave with fairly high flow. Let's say you start with doubles filled to a volume of 300 cubic feet (nearly the volume of 4 AL 80s). You swim into the current until you have used 100 cubic feet, and then turn, using far less gas on the return with the current. You go back to the shop with 150 cubic feet in the tank (nearly 2 AL80s), and they fill it back to 300 cubic feet. You do not want to be charged for the nearly 2 full AL80s that you already had. In standard OW diving, you usually bring your tank back reasonably empty.

 

[The Chairman]

In cave country they charge by the cubic foot.

If it's not air. Air has a set price per tank.

I think I'll work on my fill station today.

 

[rob.mwpropane]

Generally, technical shops charge by the cubic foot. You pay for the gas you get.
It helps promote safer reserve gas usage as there is never a reason to drain a tank down. You don't save any money by cutting out your reserves.

I knew that they did this, but I didn't know the reason why. Good stuff.

I just figured enough cave divers bitched about it and they agreed to charge / cf... but your answer is much better, lol.

 

[Lorenzoid]

As Manatee Diver said, there is a big difference in procedure in cave country because there is a big difference in volumes. Let's say you are diving to thirds in a cave with fairly high flow. Let's say you start with doubles filled to a volume of 300 cubic feet (nearly the volume of 4 AL 80s). You swim into the current until you have used 100 cubic feet, and the turn, using far less gas on the return with the current. You go back to the shop with 150 cubic feet in the tank (nearly 2 AL80s), and they fill it back to 300 cubic feet. You do not want to be charged for the nearly 2 full AL80s that you already had. In standard OW diving, you usually bring your tank back reasonably empty.

One time I brought my doubles in to the fill station, and when they saw the somewhat low pressure reading they said, "Either you had a really bad day or you've been practicing skills in open water." LOL. Yes, it was skills practice.

 

[rjack321]

1500psi in an al80 = 48cf
Florida math lmao


(suggestion: go someplace smarter)

 

[Superlyte27]

Are Florida cave diving shops selling hot gas?

I returned to Florida caves with my transmitters and being the numbers nerd I am I decided to take a little time at the end of the week to calculate my gas usage. I was wondering if the fill card I had on file was enough to cover my week of diving. When I went to close my tab at the dive shop I already had my cu ft usage in a spreadsheet on my phone and it was much less than what the shop calculated. So I asked how they calculate it. The answer was something like:

We record your starting pressure, then fill your tank to rated pressure and record the cubic feet used. Then we let it cool and top it off recording that additional volume.

An example to illustrate:

You bring an AL80 in with 1500psi. They fill it to 3,000 and add 40 cu ft to your bill. It cools down to 2,700 in the water bath and they top off to 3,000 and add another 8 cubic feet to your bill. You end up with only 40 cu ft of additional gas, but they sold you 48.

Do other shops do this?

I record your starting pressure…
If you came in with an LP85 with 1800lbs, I’d fill to 4000 and charge you for 3600, which is what it would cool to.

 

[Superlyte27]

There’s actually another thread in the last few days regarding bad practices of a dive shop in the exact area. You might search it out to see why no one is using bad dive shops. It’s also a reason I might consider resurrecting a fill station nearby.

 

[lukeb]

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