Tank - Difference Between Bar And Psi

[lunaticgate]

Hi, I have a question about the difference between BAR and PSI.
Usually I use a 12l steel tank filled to 200 bar (sometimes 230 bar) but the last time in Palau I used a Faber HP100 filled to 3000psi.

Searching on the web I found this on the Faber website:

"HP steel 100

This versatile tank provides 99.5 cubic feet of gas with a 3,442 psi fill, and 87 cubic feet of gas with a 3,000 psi fill. That’s 10 cubic feet more gas than you’d get with an aluminum 80, and 17 cubic feet more gas than a HP steel 80 at the same fill pressure. So even when you can’t hook into a high-pressure fill station you can still score a hefty load of gas for extended bottom time, with a tank that’s very similar in size and weight to a HP steel 80.
Also, like the HP steel 80, the HP steel 100 has excellent buoyancy characteristics. Ranging from 10 pounds negative when full to 2.5 pounds negative when empty, a properly weighted diver switching from an aluminum 80 to a HP steel 100 could theoretically shed five and a half pounds from his or her weight system."

Now, reading the above description, seems I used a 87CU (99.5 filled to 3000psi).
Is it correct? So can I compare it with the 12l steel filled to 200bar or my calculations are wrong?

My final goal is understand my air consumption, thank you!

 

[matt_w]

87cuft is about 2463 liters and a 12l tank at 200bar is 2400 liters. Seems close enough for me. And of course their 87 is actually like 86.7 so they are nearly identical.

 

[2airishuman]

The Faber FX-100, which is what you probably used, is a 12.9 liter tank. A 12 liter tank filled to 200 bar (2900 PSI) would have approximately 10% less air than a 12.9 liter tank filled to 3000 PSI (206.8 bar).

 

[matt_w]

The Faber FX-100, which is what you probably used, is a 12.9 liter tank. A 12 liter tank filled to 200 bar (2900 PSI) would have approximately 10% less air than a 12.9 liter tank filled to 3000 PSI (206.8 bar).

You may be right, but 12.9 at 206.8 bar is more than 2667 liters which would be 94cuft and you would think they would have said that in the promo material.

 

[2airishuman]

I'm not sure how they do their figuring. Air isn't perfectly compressible, and the exact conditions of temperature and pressure that define a square foot can throw off the calcs considerably. I'm not sure if 0 bar = 0 PSI for the purposes of a standard cubic foot of air.

 

[matt_w]

I'm not sure how they do their figuring. Air isn't perfectly compressible, and the exact conditions of temperature and pressure that define a square foot can throw off the calcs considerably. I'm not sure if 0 bar = 0 PSI for the purposes of a standard cubic foot of air.

Well Faber does sell different models of hp100 that appear to hold between 99.5 and 102 cuff at.the same pressure. Best bet for the OP is to calculate the SAC for each tank and the even with the variance it is within a few %, which is much more accuracy than anyone's sac calculation actually deserves.

 

[DA Aquamaster]

Let's do some basic math.

99.5 cu ft / 3442 psi = .0289 cu ft per psi.

.0289 cu ft x 3000 psi = 86.72 cu ft.

1 bar = 14.5 psi, so

14.5 psi x .0289 cu ft = .41905 cu ft

and

.41905 cu ft = 11.866 liter.

Which makes the FX-100 an 11.9 L tank, given normal manufacturing tolerances, and not a 12.9 L tank.

However, an 11.9 L tank has less than a 1% difference in volume compared to a 12 L tank.

3442 psi = 237.38 Bar,

237.38 x 11.9 = 2824 L
237.38 x 12 = 2849 L

That's a difference of only 25 liters, or 0.88%.

It's ok to call it a 12 L tank and dive it accordingly.

 

[lunaticgate]

In the reservation they wrote "100 Cubic Foot Steel Cylinders" and I found the Faber steel tank, so I'm not sure about the model. The only parameter is the PSI, always filled to 3000psi.