What is the correct pressure when PST 120 filled hold 120 cu ft?

[in_cavediver]

Did you guys add 14.7psi to each value to make them absolute pressures?

Absolute only matters if the specs are absolute. In theory, that 14.7 PSI would not act on the bearing surface. One side of the yoke, 3442 PSIG or 3457.7 PSI. The other, 0 PSIG or 14.7 PSI (ambient pressure). The delta P is 3442 in both cases.

Then again, if 14.7 PSI would make any real difference, your way to close to the failure point and really ought to rethink it.

Mike

 

[LUBOLD8431]

Yes, but you realize your calculation is no different then his? Multiplication and division are distributive. (3000/3442)*120 is the same as 120/3442*3000 and any other ordering. The only real difference people will see is error from a calculator. That is limitation of the hardware used not the physics or the math.

Mike

Yeah, I know its the same thing, but my way makes more sense.

 

[Otter]

Yeah, I know its the same thing, but my way makes more sense.

3000/3442 = the % full x 120 (the capacity of the tank). What does your mean again :1poke:

 

[padiscubapro]

Yes, but you realize your calculation is no different then his? Multiplication and division are distributive. (3000/3442)*120 is the same as 120/3442*3000 and any other ordering. The only real difference people will see is error from a calculator. That is limitation of the hardware used not the physics or the math.

Mike

Remember those are IDEAL calculations, the volume actually varies based on the gases varying compressibility at various pressures, temperatures AND what gas you are puttting into the tank.. Gases with higher oxygen percentages will have a larger free volume of gas available (in general) put some Helium into the mix and the capacities drop..

FOR AIR Below 2050 psi you have more than calculated, for a 3000 psi AIR fill divide the output by 1.032, for a 3442 psi fill divde by 1.051, for 3500 divide by 1.054..

In the PST specs they dont specify the gas.. and if its actually the REAL capacity not IDEAL.

Following calculations are for STP
Lets assume its an ideal calculation of capacity so at 3442 it holds 114.18 cuft of AIR, if it was 100% oxygen (not that I would fill o2 that high) it would be 125.39 cu ft, for 100% helium it would be only 107.29

SO until PST publishes the figures stating what gas they used, what temperature it was at and if its actual gas delievered all calculations are best guess estimates..

WIth the liquid capacity we could figure out what the real amount of gas is.. This is how its done in the metric system and then it could be adjusted for gas compresibilityif you wanted to get anal...

 

[LUBOLD8431]

3000/3442 = the % full x 120 (the capacity of the tank). What does your mean again :1poke:

Whatever, too tired to fight... I give up.

 

[Warren_L]

3000/3442 = the % full x 120 (the capacity of the tank). What does your mean again :1poke:

Charles is correct - multiplication and division is distributive. Simply, 120/3442 x 3000 breaks the calculation down to cubic feet per PSI times the total PSI you wish to achieve. Same result, really.

 

[The Chairman]

Uh, in_cavediver... the was put there to show how silly the debate is getting. I was not recommending that we convert to absolutes (pressure AND temperature) in order to see how many angels can dance on top of the valve. It is way COMMON for manufacturers to round their figures UP. Steel 72s only hold that volume IF they are plus rated and filled to the plus rating... even then they are shy .6cf. An AL 80 holds less than that @ 3000psi % 80 F, but it varies for each tank manufacturer. I would imagine the same holds true for any tank.

Tank volumes are guesstimates ONLY. If you are trying to figure your consumption down to the cf, then you have really missed the whole point.

 

[padiscubapro]

Uh, in_cavediver... the was put there to show how silly the debate is getting. I was not recommending that we convert to absolutes (pressure AND temperature) in order to see how many angels can dance on top of the valve. It is way COMMON for manufacturers to round their figures UP. Steel 72s only hold that volume IF they are plus rated and filled to the plus rating... even then they are shy .6cf. An AL 80 holds less than that @ 3000psi % 80 F, but it varies for each tank manufacturer. I would imagine the same holds true for any tank.

Tank volumes are guesstimates ONLY. If you are trying to figure your consumption down to the cf, then you have really missed the whole point.

for most AL 80s, 77.4 is the norm....

 

[Otter]

Whatever, too tired to fight... I give up.

I know, just goofin.

 

[GDI]

You can find out what the cu ft of a tank will be at any fill pressure by knowing the baseline of that tank and then some simple math. Baseline = (Cu ft / rated fill pressure) *100
And you will have the cuft per 100 psi = Baseline