Plumbing your shop for gas

[zoama]

(Maybe my math is off, but it looks like it'd take at least 13cf just to prime a 100' 1/4" hose - much more depending on the pressure.)

Cheers,
Richard

It would take 59 cubic inches to fill a line 1/4" x 100' or about 1/29th of 1 cubic foot (1728 cubic inches). Pressure is irrelevant.

[Rambozo]

It would take 59 cubic inches to fill a line 1/4" x 100' or about 1/29th of 1 cubic foot (1728 cubic inches). Pressure is irrelevant.

Pressure of a compressible gas is totally relevant for that calculation.

[zoama]

Pressure of a compressible gas is totally relevant for that calculation.

Any pressure great enough to escape the bottle would purge the line. If I'm wrong please explain.

[Rambozo]

Any pressure great enough to escape the bottle would purge the line. If I'm wrong please explain.

True, as long as you did not let the pressure increase. But it will take the volume of the line for every 14.7 psi to bring it up to that pressure in the line. Then if you open the line you will lose that pressure and have to replace it. So for 50psi line pressure you will need aprox. 4.5 times the line volume of gas to get that pressure.

So for the example: 1/4" ID 100' hose: it would be about 265 cubic inches of gas. Or just over .15 cubic feet, not counting hose expansion due to pressure.

[zoama]

True, as long as you did not let the pressure increase. But it will take the volume of the line for every 14.7 psi to bring it up to that pressure in the line. Then if you open the line you will lose that pressure and have to replace it. So for 50psi line pressure you will need aprox. 4.5 times the line volume of gas to get that pressure.

So for the example: 1/4" ID 100' hose: it would be about 2650 cubic inches of gas. Or just over 1.5 cubic feet, not counting hose expansion due to pressure.

Any pressure great enough to escape the bottle would purge the line. The line would contain a higher volume with increased pressure but that would remain behind a quick coupling and not come into play.
As the bottle empties, the line and bottle pressure would eventually equal atmosphere together.

What formula are you using to calculate the volume ?

[Rambozo]

Any pressure great enough to escape the bottle would purge the line. The line would contain a higher volume with increased pressure but that would remain behind a quick coupling and not come into play.
As the bottle empties, the line and bottle pressure would eventually equal atmosphere together.

What formula are you using to calculate the volume ?

With good couplings you would not lose much, but if you opened the line or lost the line pressure due to leaks, that is what it would take to refill the line to pressure. Some shops lend themselves to plumbed lines, others to bottles on each cart. I prefer keeping a few different sized bottles around. Portability and backup for when I forget to get something filled.

I was so busy trying to copy the math symbols into that post, (total fail) I misplaced a decimal. You caught me before my edit.

[RichardH]

It would take 59 cubic inches to fill a line 1/4" x 100' or about 1/29th of 1 cubic foot (1728 cubic inches). Pressure is irrelevant.

You are correct - my math was off by a factor of 12 (I divided by square feet instead of cubic feet). And I agree the pressure is irrelevant to the volume of the line itself, and the amount of gas needed to purge it.

But based on experience with my air compressor, I expect that a pressurized line will bleed out overnight to equalize with atmospheric pressure, so it'll need to be re-pressurized at the next use. That amount is "wasted", and an oversized line wastes more. (I wouldn't expect it'd need to be re-purged, since the line didn't get contaminated, it just lost some content.)

As you point out, the math is not as bad as I thought. I'll need to measure the regulator's output to see what pressure it lets the output line charge to.

Cheers,
Richard