Lp 95 comparison

[db_cooper]

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.

 

[Caveeagle]

Be really careful over-filling the typical LP72. There is plentiful debate to had around the discussion on over-filling of LP steel tanks , but I think very few would disagree that's the older 72s should be given extra care.

But in general terms...

72cf / 2250psi = .032 cf/psi
.032 * 2500psi = 80cf

I have seen LP72 that got the + stamp at hydro for a 10% overfill.
72cf @2250 psi +10% = 2475psi *.032 =79.2cf.
..so you are pretty much right there. ...but I personally won't go too much above that.
*now there are more modern iterations of a LP72, that are stronger tanks,,

 

[Caveeagle]

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.

 

[rongoodman]

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

My understanding is that their capacity is 95cf@2650psi. Other LP tanks are rated in a similar manner.

 

[Caveeagle]

My understanding is that their capacity is 95cf@2650psi. Other LP tanks are rated in a similar manner.

Yea, I think you are right about that. It can be confusing because nearly all my tanks have 2400 stamped on them and not all of them have the + stamped on them.

http://www.indianvalleyscuba.com/se...ction/information/CYLINDER SPECIFICATIONS.pdf

This chart seems to back up the nominal ratings (i.e. LP 95). Seem to include the +10%.

So just do the same math with 2650 to get your psi/cf.

You can also see on the chart that actual capacity it not always consistent with the nominal ratings. For example a Faber 108 and OMS112 are the same tank. The chart above and the Huron valley chart disagree with the actual capacity. FWIW, I suspect a typo on the IVS chart. The OMS nimonal ratings already include the +10% where the faber standard does not (in this case).

So it's best to do your own homework, double check everything, and always be conservative in gas planning.

 

[tbone1004]

@Caveeagle the 72's are 72cf at 2475 psi, 2250+10%
the non-linear compression doesn't really start coming into play until the mid 3000's so it is pretty darn close to linear, but either way the non-linear compression just adds conservatism.

A LP95 has ~95cf at 2640 psi. A LP72 would have to be pumped up to 3300 to have similar capacity. I regularly fill mine to 3000 and have no problem doing so *their hydro pressure is still 3750 and have to be able to withstand many thousands of hydro cycles*, and 3000 gives me about 85cf which is a nice gas buffer over AL80 divers if I'm diving singles

 

[tursiops]

You get fewer breaths of gas (at a given depth) from the first 1/3 of your tank, than the last 1/3rd.

?? Can you please explain this further?

 

[Trace Malinowski]

?? Can you please explain this further?

Because divers typically waste 4 or 5 to make sure each regulator works prior to diving.

 

[tbone1004]

?? Can you please explain this further?

assuming a 90cf tank at 3000psi for easy math. You would assume that for each 1000psi, you would get 30cf. From 0-3000 that is basically true, so you'd have 60cf at 2000psi, or 30cf at 1000psi, but you would only have say 110cf at 4000psi.

At 2000psi it is essentially linear, at 3000psi it is off by 3% which is still pretty irrelevant. At the 3600psi cave fills, it is off by about 6%, and at 4300psi *true 300bar*, it is off by 11%. So at 4000psi, you think you would have 30cf more than you did at 3000psi, but in reality you would only have about 20cf more.

 

[tursiops]

assuming a 90cf tank at 3000psi for easy math. You would assume that for each 1000psi, you would get 30cf. From 0-3000 that is basically true, so you'd have 60cf at 2000psi, or 30cf at 1000psi, but you would only have say 110cf at 4000psi.

At 2000psi it is essentially linear, at 3000psi it is off by 3% which is still pretty irrelevant. At the 3600psi cave fills, it is off by about 6%, and at 4300psi *true 300bar*, it is off by 11%. So at 4000psi, you think you would have 30cf more than you did at 3000psi, but in reality you would only have about 20cf more.

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....