How low makes a difference?

[swimmer_spe]

I dive with steel 120s. They are filled to ~3500psi. If they only filled it to 3000psi, how many cu ft would I loose? How much could I loose before I would notice it?

I am an airpig.

 

[lonebrave]

120cf @ 3500... at 3000, that would be about 102xf (120*3000/3500)....as to how much before you would notice, that's your call.

 

[swimmer_spe]

So, I get almost 10 percent less...

 

[Dr. Lecter]

13-15% less and change, depending on whether they're 3442psi or actual 3500psi.

 

[swimmer_spe]

13-15% less and change, depending on whether they're 3442psi or actual 3500psi.

3442 psi, but I could not remember the exact number.

 

[idive2]

I dive low pressure tanks so maybe not an exact comparison. As a low pressure tank owner we usually get
a bit more than service pressure depending on the shop. After getting used to a bit more and than recently
getting actually a bit less than service pressure I can say the difference is very noticeable. Actually receiving say
300 psi more or 300 psi less in a low pressure tank is a greater percentage change in a low pressure tank. The upside
is the extra psi is a greater gain.

 

[spectrum]

I dive with steel 120s. They are filled to ~3500psi. If they only filled it to 3000psi, how many cu ft would I loose? How much could I loose before I would notice it?

I am an airpig.

First off you need to reserve 500 for the sake of shabby gas planning. This means you get to dive 2500 or 3000 PSI of air. The 500 PSI equates to a 1/6 reduction.

 

[Jim Lapenta]

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)

 

[TSandM]

You've already gotten the answer about the drop in volume with the drop in pressure. I just wanted to add that there are ways to work on dropping your gas consumption . . .

 

[swimmer_spe]

You've already gotten the answer about the drop in volume with the drop in pressure. I just wanted to add that there are ways to work on dropping your gas consumption . . .

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.