Tank Pressure and Volume

[modivin]

Can someone please straighten me out on tank volume and pressure as it relates to HP and LP tanks? I'm sure there is a thread somewhere that has the formula and that can explain how much a tank can hold relative to a certain pressure. i.e a LP 108 at xxx psi cantains xxxx cu ft......

I'm just getting back into the sport and any and all help would be appreciated and many thanks...

Mark

 

[Charlie99]

Ignoring the percent or two error caused by air not being an ideal gas the free volume of gas is just proportional to pressure.

Current Volume = Rated Volume * (Current Pressure/Rated Pressure)

Example: A tank that has 108cu ft at 2640 psi will have 108/2640*3000= 122 cu ft at 3000psi.

 

[spectrum]

The tank will hold it's rated volume at it's rated pressure. There's no formula for that, it's the spec.

Do you want to know what a given tank will hold at a different pressure?
Take an E7-80, 80 cubic feel at 3442 PSI
80 / 3442 = .0232 cubic feet per psi

so at 3000 PSI
3000 x .0232 = 69.6 cubic feet

Is that what you're looking for?

As for HP and LP each have their own specs and the math is all the same.

Pete

 

[modivin]

The tank will hold it's rated volume at it's rated pressure. There's no formula for that, it's the spec.

Do you want to know what a given tank will hold at a different pressure?
Take an E7-80, 80 cubic feel at 3442 PSI
80 / 3442 = .0232 cubic feet per psi

so at 3000 PSI
3000 x .0232 = 69.6 cubic feet

Is that what you're looking for?

As for HP and LP each have their own specs and the math is all the same.

Pete

I guess I'm looking for the volume at, say, 3000 psi overfill for a standard 95 CF tank vs the 2640 overfill.

Thanks!

 

[modivin]

Ignoring the percent or two error caused by air not being an ideal gas the free volume of gas is just proportional to pressure.

Current Volume = Rated Volume * (Current Pressure/Rated Pressure)

Example: A tank that has 108cu ft at 2640 psi will have 108/2640*3000= 122 cu ft at 3000psi.

YES! Thats the one. Was never really good at math...but that's the formula I was looking for. Thanks!

 

[Diesel298]

I guess I'm looking for the volume at, say, 3000 psi overfill for a standard 95 CF tank vs the 2640 overfill.

Thanks!

that same formula will work for that too...
i have faber lp98's at 2640 and i often over fill them to 3500
so
tank size / rated pressure =
98 2640 .037 (thats the psi per cubic foot)

now take that and multuply it by whatever pressure you have or want to nkow what you volume is say 3500 psi in that tank =129.5

i just did this a minnute ago actually...
i have double lp 98 fabers
im diving tomorow with somone who has a 120
i only have 2000 psi in my doubles.....
so 98x2 is my rated volume at 2640psi
so i get .074 multuply that by 2000 (current psi)= 148 cuft...
so ill be good

good? questions.....more examples...
i love dive planning.. its a sickness.......

 

[Skeeter1097]

A ip121 at 2400lbs = 121ft of gas. fell it to 3600lbs and you have 165. The same as 2 80"s or close to. But most shopes well only fell it to 3000 you stell have 145 or close to

 

[A. Dale Fox]

This is an interesting series of mesages and replys. While the math is correct, the law is not. In the United States it is illegal to overfill a cylinder beyond its authroized service pressure except for the 10% excess fill authorized for certain "+" cylinders.

 

[Walter]

Dale, are you a friend of Jill Robinson's?

 

[Drew Sailbum]

Well hello Dale! I took my PSI Cylinder Inspector course from you a couple years ago here in Cayman. Welcome to the board.