Question Internal volume of gas transfill hose (whip) with analog gauge

[LFMarm]

I am refining a calculation sheet to see how many CCR tanks I can refill with a cascade of doning tanks. I know that most likely it will not make a big difference, but I would like to include the internal volume of the whip that gets lost every time a transfill is done. Anyone has an idea of internal diameters / volumes of something like this:

It's 60 in | 1.5 m long with standard DIN fittings; it has a 2 in | 5.1 cm gauge with boot; the hose has a 5000 psi | 350 bar working pressure.

 

[rob.mwpropane]

Can always install a valve to avoid expensive gas loss? @tbone1004 would know the math

 

[Johnoly]

1/4" inside diameter hose Times 30 inches = .001 cubic feet at ambient pressure.

You can factor in psi,temp, elevation, sunshine/cloudy, day of the week, mother's maiden name, and it's still just a rounding error compared to total volume as you can see above.

 

[tbone1004]

Volume a cylinder for a 60" hose with 1/4" ID is 2.95ci, plus a couple inches for fittings so 3.25ish cubic inches is .00188cubic ft so call it .002 for less digits. If you want to be pedantic you can always fill it with water and get the actual water volume but I'd bet we are within 5%.

If you equalize at 3000psi, that's 206 bar, call it 200 for easy math, 200*.002 yields roughly 0.4cf inside the hose when it equalizes at 3000psi, plus or minus a bit for rounding errors, exact length and ID, etc but close enough. Goes up a bit if the pressure is higher, goes down if pressure is lower so ~0.25cf at 2000psi. Adding a line valve on the receiving side will stop the vast majority of that gas loss since you'll only be bleeding what is in the fill block itself.

 

[inquis]

Do you intend to drain the CCR tanks each time? If not, the difference from assumed level will overwhelm the lost whip volume in any calculation.

 

[LFMarm]

Thanks all for chipping in. Not surprised that this is negligible but easy to add to my Excel.

Yes, I drain every time my O2 tank for air travel. During the dive trip, I never go below 10 bar to avoid water ingress.

 

[JohnN]

I am refining a calculation sheet to see how many CCR tanks I can refill with a cascade of doning tanks. I know that most likely it will not make a big difference, but I would like to include the internal volume of the whip that gets lost every time a transfill is done. Anyone has an idea of internal diameters / volumes of something like this:

View attachment 795552​

It's 60 in | 1.5 m long with standard DIN fittings; it has a 2 in | 5.1 cm gauge with boot; the hose has a 5000 psi | 350 bar working pressure.

Measure with a micrometer
Mark with chalk
Cut with an axe
Hammer to make it fit
Paint to cover up the mess