Dear friends...do you remember the question about the temp used in volume calculations??..here the answer i received from lufex about the method they used for determined it...
this follows:
Dear Sir,
Thank you for your recent enquiry via our website, I apologise for the
delay
in replying to you.
I belive that you have been looking at the values given for our US
cylinder
range and so I have been in touch with a colleuague in the USA and
asked for
his comments on your query. His reply was as follows:
"We have traditionally used data published by the Department of
Explosives
(now Department of Weights and Measures, I believe). This data was
published for the compressibility of air at standard room temperature
of 70F
(21C). This data was originally printed in the early 70's and so could
be
outdated. The way the calculation works is as follows:
Take the internal volume of the cylinder divide by a residual gas
factor for
the pressure in question which gives the standard cubic foot capacity
of the
cylinder.
The data we use may be slightly different to other published values by
other
organizations. It should all be relatively close however. Also please
bear
in mind that we do some rounding of the numbers to come up with the
capacity. So although an S80 will state 80 cu ft of air at 3000 psi,
the
real number could be anywhere from 75 to 84.9.
The residual gas factor I have for air at 3000 psi is 8.763 cu in water
capacity/cu ft of air. The internal volume of an S80 is 678 cu in.
Therefore, in this case, the capacity in cu ft is 678/8.763 = 77.37 cu
ft of
air."
