HP, LP? what this all about

[H2Andy]

well ... if you open the valve, the gas inside will flow out until there's a pressure equalization ... so ...

if the inside and the outside of the tank are equally pressurized, that means that inside the tank there is some gas left? equal to whatever volume the tank is ... so, for example, in a 12 ltr tank, there will be 12 ltrs of air inside

(i better be right on this one)

 

[xiSkiGuy]

While we're on capacity.....
Does the rated (US) capacity of let's say 100 cubic feet include the first atmosphere of volume that will never leave the cylinder except under a vacuum?

Yes I know this is nit picking but it just occurred to me that this must approach 1% on an 80 CF cylinder.

Pete

If you hook up a regulator to a tank that only contains "ambient" (above water) pressure, what does the SPG say?

 

[spectrum]

If you hook up a regulator to a tank that only contains "ambient" (above water) pressure, what does the SPG say?

Well it says zero of course, that does not answer the question.

 

[H2Andy]

Well it says zero of course

exactly, of course!

(good answer)

 

[xiSkiGuy]

Well it says zero of course, that does not answer the question.

I would assume that because we call that same tank "full" when that same SPG reads 2640 (or 3000, or 3300, or 3442) that it does not include ambient. But I'm just assuming. :no

On the other hand, tank capacity naming in the US is just picking a number that is close and sounds cool. For example: are you sure those 104s and 108s are 4cf different when the exemption version of both is called a 130? :huh: My point being that ambient isn't that significant when the names of the tanks aren't necessarily exact either.

 

[H2Andy]

for the record, i don't really know the answer

but zero has the right ring to it!

 

[spectrum]

for the record, i don't really know the answer

but zero has the right ring to it!

For the record I know don't either.

It was a serious albeit trivial question though.

 

[Jimmer]

On the other hand, tank capacity naming in the US is just picking a number that is close and sounds cool. For example: are you sure those 104s and 108s are 4cf different when the exemption version of both is called a 130?

Perfect example is my OMS LP108's, which very clearly have "112 cubic feet" stamped on the shoulder

 

[Colliam7]

Does the rated (US) capacity of let's say 100 cubic feet include the first atmosphere of volume that will never leave the cylinder except under a vacuum? Yes I know this is nit picking but it just occurred to me that this must approach 1% on an 80 CF cylinder.

It seems it would have to (include the residual volume). Oooh, this is just like pulmonary function testing, isn't it? What is the LV, the FVC, and the RV (residual volume)?

If a nominal 100 cf tank (E7 steel 100) is rated to hold 100 cf at 3442 PSI, and holds 89 cf at 3000 PSI, and 80 cf at 2640 (data from tank websites) then the conversion factor is between 0.03030 (at 2640 PSI) and 0.02905 (at 3442 PSI) cf / PSI, with the difference in proportions being practically immaterial. Multiply 0.02905 by 14.7 PSI, or 0.03030 by 14.7 and you get between 0.427 and 0.445 cf. That means the usuable capacity is about 99.55+ cf. Even if you assume that the rated capacity does NOT include the residual volume, the usuable capacity changes by an insignificant amount - 100 cf vs 99.55 cf.

 

[xiSkiGuy]

Perfect example is my OMS LP108's, which very clearly have "112 cubic feet" stamped on the shoulder

That's a great example because that OMS 108 is actually a rebadged Faber 108 and TDLs tank chart lists both as "actually" having a 108cf capacity.