How much air does an LP85 hold at 2400 PSI?

[Ghetto Diver]

the old lp76 and the newer lp85 are very similar because the old lp76 was quoted at 2400 psi (and didn't come with a plus rating from the factory).

Mine has a factory +, so...

 

[CaveSloth]

Mine has a factory +, so...

I think mine does too.

 

[tursiops]

Wow. Ok well then I guess I’ll start telling them I have an LP76 and save some money since it seems the tank size can’t actually be determined.

The tank size CAN be determined. The tank can be filled with water, and the volume of water measured. Then some algebra. You do NOT want to do this now, but it would be pretty easy at the next hydro. After all, they fill the tank with water to test it....
You can also get another data point by weighing the empty tank with no valve on it. then you go to the manufacturers tables and look it up.....pressure, weight, diameter, length.
right now we are guessing because they are doubled up so hard to weigh.

Here is some cylinder data:
SCUBA Cylinder Specifications – Huron Scuba, Snorkel & Adventure Travel Inc. PADI 5 star IDC in Ann Arbor, MI
The only 2400 psi steel tank with 7 inch diam and 26 inches long is the OMS 85, which I think (not sure) was made by Faber.
Some more data:
http://vzafc.rkvln.servertrust.com/v/vspfiles/photos/Faber-Cylinder-Specifications.jpg
The only 2400 psi steel tank with 7 inch diam and 26 inches long is the L85DVB, shown as 13 liters water volume.
Both of the tanks above weigh 31 pounds empty, no valve.

One more way to approximately sort this out: Fill the tank (2400) with air and weigh it in water.
Drop the pressure down to (say) 400 psi and weigh it again; call 2400-400=P. Remember air weighs about 0.08 pounds/cuft, at standard temp and pressure.
The difference in weight (W) is the weight of the air: P/2640 * X = W/.08, or
X=W*2640/P/0.08.
Example: Let P = 2000 psi, and W = 5.2 pounds. then X = 86 cuft.

 

[runsongas]

Mine has a factory +, so...

26 inches tall not including valve and boot?

 

[CaveSloth]

Can't I just weigh the whole doubles set before and after filling? Then I would have a PSI difference and a weight difference. Making up random numbers here:

Hypothetical BS numbers:

Before filling: 1500 PSI, 78lbs
After filling: 3500 PSI, 88.3lbs

10.3 lbs of air = 2000 PSI

Therefore...

13.6 lbs of air = 2640 PSI

Therefore...

Tanks would hold 170cf at 2640, or 85cf each... (like I said, bs numbers)

 

[Ghetto Diver]

26 inches tall not including valve and boot?

Yes. Actually 26.5" if I recall.
This is why I made my post to begin with as it seems it is a match to the op's.

 

[runsongas]

the lp76 is something like 83.5 cf with the + rating overfill. for practical purposes it is nearly identical to the lp85. the capacity was just quoted differently.

 

[Ghetto Diver]

No..the stated volume is 75.8 at 2640 (with the +).
Fuzzy pic taken with a potato lense, but its there..tank is narrow though.

 

[tursiops]

Can't I just weigh the whole doubles set before and after filling? Then I would have a PSI difference and a weight difference. Making up random numbers here:

Hypothetical BS numbers:

Before filling: 1500 PSI, 78lbs
After filling: 3500 PSI, 88.3lbs

10.3 lbs of air = 2000 PSI

Therefore...

13.6 lbs of air = 2640 PSI

Therefore...

Tanks would hold 170cf at 2640, or 85cf each... (like I said, bs numbers)

Should work. But hard to weigh....do it in a swimming pool?

 

[BrackaFish]

I believe that the OP should be able to look at the stamped marking on the tanks to determine the size. All 4 of my Faber LPs have BS85 or BS95 stamped on them.