How low makes a difference?

[spectrum]

I am improving the more I dive. I used to be a lot worse, but, over time I have learned a few tricks to keep it low. Things like getting used to the cold water, waiting to go on air until I have control of my breathing....

I would love to have a nice long no deco dive and still have over 1000psi.

It sounds like you are on the right track. Just keep at it. You are still very early in the game.

Pete

 

[PeterNBiddle]

as I explain to my OW students the way to convert PSI to cu ft is done by dividing the cu capacity of the tank by it's working pressure to give you a cu ft per PSI figure. You then multiply that by the actual pressure in the tank to give you the actual fill.

so for a 3442 HP 120 you divide 120 by 3442 which gives you .03486. Take that times 3000 and you are diving a 104.59 tank. so you are losing 16 cu ft of gas roughly.

And this is why I dive LP tanks. Take my LP95. Fill it to what I usually do around 3200.

Using the same formula 95/2640 = .03598 x 3200 = 115.15 a net gain of 20 cu ft and not uncommon in cave and wreck fills here in the Northeast. And even if I only get a 3000 psi fill I'm still diving a 108 (107.954)

Posts like this are one of the reasons I LOVE scubaboard. I didn't grok the practical reality of a "smaller" LP tank out-performing a "larger" HP tank at the same LP PSI fill.

Thanks Jim!

 

[maniago]

Posts like this are one of the reasons I LOVE scubaboard. I didn't grok the practical reality of a "smaller" LP tank out-performing a "larger" HP tank at the same LP PSI fill.

Thanks Jim!

Well now hang on there Cowboy. If you over pump anything you get more. If the OP over pumps his 120 by the same 21% Jim is doing to his 3AL tanks, don't you think the OP will also get more to work with too? But nothings for free. There is plenty on the metallurgy of AL vs Steel tanks, so no need to belabor that here. As we say in aviation, if you exceed what the mfg specified, you've now become a test pilot. Same goes with tanks (or anything else I suppose). Yes people do it. Doesn't make it right or safe. If you decide to go there, just make sure you've thought about what your life insurance company will do...

 

[PeterNBiddle]

Well now hang on there Cowboy. If you over pump anything you get more. If the OP over pumps his 120 by the same 21% Jim is doing to his 3AL tanks, don't you think the OP will also get more to work with too? But nothings for free. There is plenty on the metallurgy of AL vs Steel tanks, so no need to belabor that here. As we say in aviation, if you exceed what the mfg specified, you've now become a test pilot. Same goes with tanks (or anything else I suppose). Yes people do it. Doesn't make it right or safe. If you decide to go there, just make sure you've thought about what your life insurance company will do...

I'm not sure you read my post exactly. I said on the same LP fill, which at 3000 PSI, as Jim points out, would let an LP95 out perform an HP 120.

Obviously if we fill both tanks to their rated fills they perform to their ratings.

 

[swimmer_spe]

I'm not sure you read my post exactly. I said on the same LP fill, which at 3000 PSI, as Jim points out, would let an LP95 out perform an HP 120.

Obviously if we fill both tanks to their rated fills they perform to their ratings.

I was considering the proper fill for my tank. I did round it up to 3500, because it is 34..... I do not remember the exact number. I also do not own a gauge that exact.

 

[maniago]

I'm not sure you read my post exactly. I said on the same LP fill, which at 3000 PSI, as Jim points out, would let an LP95 out perform an HP 120.

Obviously if we fill both tanks to their rated fills they perform to their ratings.

dude its not real. Youre playing with the math. Once you go over the rated pressure the divisor becomes whatever the pressure is. We call it an overfill but you dont get more cubes. The rated pressure is number the engineer came up with. Say 2640 and you over fill 10%. What if tomorrow he says oops. It should be 2750. Did you just magically lose some cu? Nope. Its the same. In reality the real volume of the tank is based on the yield pressure ie where it explodes. Thats a 100% fill. But they dont publish that. The numbers we use are safety factors.