Lp 95 comparison

[Caveeagle]

I agree with you. So why did he say what he said? He's not talking about high ;pressures. Van der Waals doesn't apply....

I just wanted to point out that the relationship is not strictly linear. I've never graphed it out, but I agree at lower tank pressures it is less of any issue. Perhaps I was splitting hairs. But in the end, we are using simplified math to estimate relative tank volumes. ...and using fairly imprecise tools.
..as Tbone stated.....fortunately, these factors all tend to add conservatism, when you play by the rules.

 

[NAM001]

recently I saw an old post here about lp 72 being filled to a particular level that would give it the same volume as an 80, 85, and 95

What is the math or is there a chart for an lp 95? If there is a formula I’m sure I can figure out now to use. Thanks I. Advance.

desired cuft divided by rated cuft times rated psi. Tihs is basic stuff but i supposed it is no longer in ow classes. since you ask about a lp95 then it is 95 cuft at (2400+10%) 2640#. so if you want 110 cuft then it is 110/95 times 2640 or 3057 psi. if yo have a lp72 that is 2250+10% and you want 80 cuft then it is 80/72* 2475 or 2750 psi. no muss or fuss about how much psi per cuft.

 

[NAM001]

And typical LP95 are
95cf / 2400psi = .0396 psi/cf
(Some charts show them at 2650psi, but that includes the 10% overfill)
.0396 * 3,000psi = 118.8cf

*i'm not advocating this... just saying this is how you look at it.

**it also important to note that relationship between tank pressure and volume is not linear. I everybody treats it that way, but its not. You get fewer breaths of gas (at a given depth) from the first 1/3 of your tank, than the last 1/3rd.

disregard

 

[NAM001]

It sounds like there are a few basic formulas the OP could learn to become familiar with. like PV=PV

 

[Scared Silly]

This is basic stuff but i supposed it is no longer in ow classes.

It is more basic than that. More like grade school mathematics ...

 

[NAM001]

It is more basic than that like grade school mathematics ...

yes but that leads to a whole other thread.

 

[Caveeagle]

Yea, I think that correction was made up thread.

I do think you have to be careful using tank rated volumes, when some might not know how the +10% factors in. Like how an OMS112 and faber108 are really the same tank. Just marketed differently.

I am sure I just confused the topic by bringing up pressure vs volume etc. (sorry). FWIW, I typically start off a dive around 3900, and noticed that first 1k psi used really seemed to be consumed a little faster than <3k psi. I am sure there are other factors, but I have strayed off topic again.

I think the OP has the answer to the original question.

 

[NAM001]

Yea, I think that correction was made up thread.

I do think you have to be careful using tank rated volumes, when some might not know how the +10% factors in. Like how an OMS112 and faber108 are really the same tank. Just marketed differently.

I am sure I just confused the topic by bringing up pressure vs volume etc. (sorry). FWIW, I typically start off a dive around 3900, and noticed that first 1k psi used really seemed to be consumed a little faster than <3k psi. I am sure there are other factors, but I have strayed off topic again.

I think the OP has the answer to the original question.

I agree, so much is taken for granted in this sport and really so little is known by new divers as opposed to many of us that have already out lived rocks.

 

[Bob DBF]

For air compressibility, and a chart, try Ideal Gas Law

On the chart 70 degrees f is about 300 degrees k.

As for 72's, an LP or MP 72 is 72 cuft at service pressure plus 10%, the old steel 72 is 71.5 cuft at 2250 +10%. The biggest problem I've seen with overfilling the old steel 72's is that the burst disk haven't been changed since the valve was first put on the tank back in the day.

I'm more apt to see an overfill due some tank monkey guessing it is an HP 100. The sizes are similar enough to confuse those that can't read. An old steel 72 at 3445#, if one were so inclined, would hold 99.5 cuft of gas.

If you need more gas, get the bigger tank. Unless you always pump your own gas, or know someone that always cave fills, there is no reliable way to have a tank overfilled.


Bob