Tank Capacity and Long Hose Question

[GLENFWB]

Two questions.

When I get a cave fill on my LP 108, I do not know what cubic foot of air that gives me. At 2640 PSI it is rated around 108 cubic foot. Anyone have a formula they can give me to figure out how many cubic feet I have at 3500 PSI?

Also, I have an Atomic B2 regulator that I need to fit with a 7 foot hose. It has a unique fitting on the end that goes in to a swivel...I am trying to avoid an adapter to eliminate another failure point. Anyone know where I can get a 7 foot hose for an Atomic regulator. My web searches haven't turned up to much.

 

[willardj]

Two questions.

1.When I get a cave fill on my LP 108, I do not know what cubic foot of air that gives me. At 2640 PSI it is rated around 108 cubic foot. Anyone have a formula they can give me to figure out how many cubic feet I have at 3500 PSI?

108/2640=.04x3500=143cf for dubs x2

2.Also, I have an Atomic B2 regulator that I need to fit with a 7 foot hose. It has a unique fitting on the end that goes in to a swivel...I am trying to avoid an adapter to eliminate another failure point. Anyone know where I can get a 7 foot hose for an Atomic regulator. My web searches haven't turned up to much.

Call Scubatoy's

 

[ucfdiver]

First find your baseline.....
108(tank size)/2640(rated pressure)=.0409psi per cu/ft.

So you then take .0409 and multiply it by the fill pressure .0409*3500=143.18.

Typically you'll just memorize that the baseline for 104/108/112 is 8.2 per 100cuft which makes the math easy. If you're gas matching with Lp120, 104, or 95's, just subtract 100psi for each larger tank size (50 for singles) and forget all the math (since you don't have a calculator in the water anyways).

Just an example, if you have 3600psi in LP95's, and your buddy has 3600psi in LP104's, here's how the math works out-
LP95s @ 3600= 129.54*2cuft
LP104's @ 3600 = 141*2cuft

So we give the LP95 diver 1200psi of penetration gas, and the LP104 diver 1100psi. With 1200psi, the LP95 diver has 86cuft of gas for penetration. Now, with 1100psi, the 104 diver has exactly 86.666cuft of gas, and we didn't even have to break out a calculator! You'll find that your math is more accurate doing it with the -100psi method than if you broke the calculator out on the surface before the tanks cooled.

Also remember that as pressure increases, the actual gas per psi drops off, this was discussed in an article written by I believe Larry Green in the NSS journal, although don't quote me on that. While an interesting fact that certainly makes you think before filling your doubles up to 4200psi to gain more gas and stressing them, you've got to remember that this just pads your margin of safety even more.

 

[DeNomad]

As a rough guess I would say around 140 cubic feet, this does not take into account real gas laws, or your tank cooling off and the pressure falling after the fill.

Just obtained using proportions ie: 108 cubic feet / 2640 psi = X cubic feet / 3500 psi.
So X = 143 cubic feet.

 

[Meng_Tze]

Way to difficult guys. mind you I am not saying you are wrong.


(3500/2640)*108 = 1.326 * 108 = 143.182 cft.

3500 is 1.326 times higher than 2640, thus the compressed volume also increases by that factor.

 

[b1gcountry]

First find your baseline.....
108(tank size)/2640(rated pressure)=.0409psi per cu/ft.

So you then take .0409 and multiply it by the fill pressure .0409*3500=143.18.

Typically you'll just memorize that the baseline for 104/108/112 is 8.2 per 100cuft which makes the math easy. If you're gas matching with Lp120, 104, or 95's, just subtract 100psi for each larger tank size (50 for singles) and forget all the math (since you don't have a calculator in the water anyways).

Just an example, if you have 3600psi in LP95's, and your buddy has 3600psi in LP104's, here's how the math works out-
LP95s @ 3600= 129.54*2cuft
LP104's @ 3600 = 141*2cuft

So we give the LP95 diver 1200psi of penetration gas, and the LP104 diver 1100psi. With 1200psi, the LP95 diver has 86cuft of gas for penetration. Now, with 1100psi, the 104 diver has exactly 86.666cuft of gas, and we didn't even have to break out a calculator! You'll find that your math is more accurate doing it with the -100psi method than if you broke the calculator out on the surface before the tanks cooled.

Also remember that as pressure increases, the actual gas per psi drops off, this was discussed in an article written by I believe Larry Green in the NSS journal, although don't quote me on that. While an interesting fact that certainly makes you think before filling your doubles up to 4200psi to gain more gas and stressing them, you've got to remember that this just pads your margin of safety even more.

***** I'm an engineer for a living, and I don't follow this.

I go with MZ, keep it simple:

Fill pressure / Rated pressure * Rated Capacity = Fill capacity


If you want to do it in your head, then 3500 is about 1/3 more than 2600, and 1/3 of 108 is about 35, so the amount of gas is about 143cf

Tom

 

[b1gcountry]

Typically you'll just memorize that the baseline for 104/108/112 is 8.2 per 100cuft

Yeah, I didn't understand it because its wrong. You mean the tank factor for double 108s is 8.2cf per 100psi. So every extra 100 psi, add 8.2cf.

Tom

 

[ucfdiver]

Yeah, I didn't understand it because its wrong. You mean the tank factor for double 108s is 8.2cf per 100psi. So every extra 100 psi, add 8.2cf.

Tom

My bad, I think you'll find aside from that typo, all the other information is correct. I agree your formula is easier, however I was trying to keep it fairly close to how the NACD workbook explains it.

 

[b1gcountry]

Definitely a typo, but I was taking you at your word, and I couldn't figure it out

Read that in a way that doesn't sound mean.

 

[ucfdiver]

Definitely a typo, but I was taking you at your word, and I couldn't figure it out

Read that in a way that doesn't sound mean.

No offense taken......it's hard to figure out tone of voice over the internet.

I think once you understand how the math is done, the 100psi trick is the easiest way to gas match that I've heard of.