Did I get double 50's?

[elmer fudd]

Not really.

Say for example that you have a set of mystery doubles rated for 1800+ with 1200 psi in them and an LP71.2 with 2475 psi. If you just hook up a transfill whip and let them equalize, then calculate the volume of added air you can easily figure out the volume of the tanks.

In this case we'll say the tanks end up equalizing with 1662 psi. Calculating for the added volume we divide 1662 by 2475 to get .671 or 67.1%. That's the percentage of air remaining in the LP71.2. We then multiply that by 71.2 to get 47.8 cf, (the air remaining in the LP72), and subtract that from 71.2 to find the volume of the air we added to the doubles. In this case 23.4 cf.

We also know that the doubles started out 60.6% full, (1200/1980) and finished 83.9% full, (1662/1980). So we added 23.3% to their total fill. Thus, 23.4 cf=23.3 percent of the total fill, and 23.4/23.3*100=100.4 cf.

Therefore we know that the mystery doubles in question were LP50's.



Now, in this case I just calculated those number to fit an imaginary set of tanks with approximately 50 cf, (I'm sure LP50's are actually closer to something else), but you can use the same formula to find actual volume and it's a lot faster than draining your tanks.

 

[duckbill]

You are correct. Thankyou.

In fact, once you know that your donor cylinder "gave" the unknown cylinder(s) 23.4CF of air, and the difference in pressure in the unknown cylinder raised by 462psi (1662-1200), you can simply calculate how many psi represents a cubic foot in that cylinder:
462psi/23.4CF=19.74psi/CF
Then, since the cylinder(s) is rated at 1980 psi, just divide the 1980psi by 19.74psi/CF to find the unknown cylinder(s) would hold 100.3CF at the full 1980psi.

... but you can use the same formula to find actual volume and it's a lot faster than draining your tanks.

True, but would you agree that the advanage of draining the unknown cylinder would be to increase the differences in pressure values used and, therefore, the precision of the measurements and calculations by reducing the margins of errors?

 

[elmer fudd]

You are correct. Thankyou.

In fact, once you know that your donor cylinder "gave" the unknown cylinder(s) 23.4CF of air, and the difference in pressure in the unknown cylinder raised by 462psi (1662-1200), you can simply calculate how many psi represents a cubic foot in that cylinder:
462psi/23.4CF=19.74psi/CF
Then, since the cylinder(s) is rated at 1980 psi, just divide the 1980psi by 19.74psi/CF to find the unknown cylinder(s) would hold 100.3CF at the full 1980psi.




True, but would you agree that the advanage of draining the unknown cylinder would be to increase the differences in pressure values used and, therefore, the precision of the measurements and calculations by reducing the margins of errors?

I'm sure it would make things a little more precise and remove some of the potential for error. You could also take advantage of having the tanks drained to inspect them and reconfigure the manifold if necessary. Of the three sets of vintage doubles I've collected, every one of them came with the valve handle facing down and the port facing up.

 

[oldmossback]

""Of the three sets of vintage doubles I've collected, every one of them came with the valve handle facing down and the port facing up."" Elmer Fudd

Sometimes there is a good reason for the rotation of the manifold valves.....sometimes not.......I had a set of twin 45's (sportsways) that I sold to Kingairpilot.......I was using a hard plastic Scubapro backpack that had a narrow top and this fitted between the bottles with long carriage bolts and a 1'x1/4" bar attached to the band bolts; I used this for diving with an old Zegale wing I bought back in the mid 80's.......this necessitated the manifold to be rotated up as there was not enough space between the tanks and backpack for a RAM.....let alone the Mk3........

I think many twin setups when mounted on backpacks had the same issues and so the manifolds were rotated........others? I suspect they are assembled incorrectly by LDS peone's.

 

[elmer fudd]

I'm guessing that it depends on the era when they were used last. Double hose divers want their ports facing down, but for single hose divers it was probably more convenient to have them facing up.