CO2/Argon big tank to little tank transfer

It is called Cross-filling, and it used to be quite common, but due to insurance reasons most shops and suppliers are forbidden from doing it.
I have a cross-fill hose for neutral gasses and one for oxygen.
The hose is a very special stainless steel braid, teflon hose, good to about 6000 psi.
These are the same hoses used on tank manifolds.
You connect each end of the hose to a tank. Open the empty tank's valve, all the way. Then open the full tank's valve all the way. The sound is quite ...surreal, as the gas rushes into the empty tank. It takes about 1 or 2 minutes for the pressures to equalize.
As a demonstration of basic physics, you will find that that the source tank gets colder and the recieving tank gets warmer.
Once the pressures have equalized, close both valves and very slowly undo one of the hose fittings. You will get a blast of high pressure gas from the hose when you break the connection, but that is just what was in the hose.
Western Enterprises sells the hoses. Any welding supplier can order one for you.

"Ernie Leimkuhler" wrote: (clip) The hose is a very special stainless steel braid, teflon hose, good to about 6000 psi. (clip) ^^^^^^^^^^^ I do this all the time with oxygen. Instead of a hose, I have two regulator/tank fittings hooked together with a high pressure elbow. The welding supply counter man who helped me set this up suggested just barely cracking one of the valves, so the fill takes place slowly. This minimizes the heating in the tank being filled.
If you close off and disconnect while the tank is still hot, you get less fill.This really only matters after the supply tank starts to get low, since that means I am not getting a good fill on my small tank
Ernie, why does it matter which valve you open first?

Good question. It is just how I was showed how to do it many years ago.

Could it be related to pressure direction? Avoid high pressure on outside of tank valve while closed? Just guessing.
Pete Keillor

Thanks, but I wonder what got the insurance companies all fired up over the practice.
I actually just saw my local distributor refill my 60ft^3 O2 bottle using the method described.
Thanks again,
d> >

I would guess opening the low pressure cylinder (empty) first lets you check the transfer setup for leaks with lower pressure gas.

The concept that semi-trained people were handling tank refills got the insurance companies worried.
All the Seattle welding suppliers stopped doing it several years ago. All the tanks go back to the plant for refill.

Any time a tank is refilled it is supposed to be checked for hydro date and a visual inspection. Most people either don't know to do this or just don't do it out of laziness, therefore worried insurance companies.
Shawn

It would be nice to have a pressure gage teed into the charging hose. This would be must have item if your were charging from 350 cubic foot with 3000 psi to 40 cubic foot cylinder rated at 2250 psi. The best time to cascade charge is from full cylinder to empty cylinder. The small cylinder might be used for protable welding or reserved for when large cylinder runs out.

if you want to figure the gauge as a nicety, i would consider evacuating (vacumm) the empty tank to be required

As described, you would put a small amount of contamination (from the air in the hose) in the tank being filled. I would leave the fitting a little loose on the tank being filled and gently crack the valve on the source tank briefly.
Ted

"Ted Edwards" wrote: (clip) I would leave the fitting a little loose on the tank being filled and gently crack the valve on the source tank briefly. ^^^^^^^^^^^^^ Another reason for doing this: If the hose has been lying around, and anything combustible has got inside, sudden application oxygen at tank pressure could cause an exposion. (Say a spider is living inside, for example.) I was taught by a welding-shop supervisor to attach theO2 regulator to the tank, but not to fully tighten it. Then crack the tank valve, and finish tightening the fitting to stop the leakage. If anything starts to go wrong, your hand is already on the wrench, so you can loosen it quickly. The same procedure would apply to the transfer hose. In fact, I would suggest blowing a little O2 through it by cracking the supply valve briefly, before attaching the empty tank.