Cave fill final gas volume

[lunaire]

Hi folks,

For cave-filling LP tanks, is there any correction factor that needs to be applied after calculating for pressure?

e.g: LP 85 has ~81 cuft at 2640 psi. When overfilled to 3500psi: 3500/2640 * 81 cuft = 107 cuft. Is this correct, or is there any more significant correction factor to apply?

 

[tbone1004]

You need to use the z-factor for your final fill pressure.

@DiveGearExpress has a good article about it

Z Factors for SCUBA | Dive Gear Express®

Z Factors for SCUBA Cylinder volume is defined by the internal dimensions of the tank, and normally measured in cubic inches or liters of water. Free capacity is ...

www.divegearexpress.com

 

[lunaire]

Ok.

Recalculated for practice:

LP 85 has ~81 cuft at 2640 psi. When overfilled to 3442psi, (3442/2640 * 81) / 1.04 = 101.5 cuft.

 

[grantctobin]

Ok.

Recalculated for practice:

LP 85 has ~81 cuft at 2640 psi. When overfilled to 3442psi, (3442/2640 * 81) / 1.04 = 101.5 cuft.

At 32% yes.

 

[DiveGearExpress]

Ok.

Recalculated for practice:

LP 85 has ~81 cuft at 2640 psi. When overfilled to 3442psi, (3442/2640 * 81) / 1.04 = 101.5 cuft.

Hmmmm, If we are going to be pedantic: While an LP85 does hold a Z-factor adjusted 81 cubic feet of air at 2640 psi, you can't use that pressure ratio adjustment and then apply another Z-factor adjustment. Start with the water volume....

Ideal capacity calculation based on Faber LP85 water volume = 13.0L

(13.0 ÷ 28.3) x 3442 ÷ 14.7 = 107 cubic feet

Then apply Z-factor correction for 32% Nitrox @ 3442 psi

107 ÷ 1.04 = ~103 cubic feet at the surface

 

[lunaire]

Hmmmm, If we are going to be pedantic:
While an LP85 does hold 81 cubic feet of air at 2640 psi, don't use pressure ratio adjustment to ideal.
Start with the water volume....

Ideal volume calculation based on Faber LP85 water volume = 13.0L

(13.0 ÷ 28.3) x 3442 ÷ 14.7 = 107 cubic feet

Then add Z-factor correction for 32% Nitrox @ 3442 psi

107 ÷ 1.04 = ~103 cubic feet at the surface

What's the origin of the 28.3 and 14.7 in your calculation?

 

[tbone1004]

What's the origin of the 28.3 and 14.7 in your calculation?

14.7psi is the standard atmospheric pressure
28.3 liters/cubic ft

 

[DiveGearExpress]

What's the origin of the 28.3 and 14.7 in your calculation?

See this rabbit hole... Calculating SCUBA Cylinder Capacity | Dive Gear Express®

 

[DogDiver]

This should help.

 

[Capt Jim Wyatt]