Welding Tips and Tricks

Just got a 40cf bottle (small),and already had much bigger bottle. The idea is to have a backup for when I'm about out on the big bottle. Also, easier to take on mobile jobs. I want to fill up the small bottle from big bottle. Will this work? Think I have read where folks use a vacuum pump before refilling themselves.

That's how scuba tanks are filled but you are dealing with dangerously high pressures...caution.

i am a certified commercial diver and i will tell you the big things you need to watch out for, one make sure your tank is always up to date on its certification, two you have the proper hoses and fittings to handle the working pressures, three do not fill too fast. as you increase the pressure the tempature will increase, if you cool the tank in a water bath do not exceed 400 psig per minute. if you do it dry do not exceed 200 psig per minute or the tank can overheat and explode. in my opinion it is not worth the risk of an exploding tank if you've never done it before, just send it to your lws and have them do it they have the right equipment to do it safely.

I frequently transfer Helium from one bottle to another, and recently filled several bottles from a high-pressure tube trailer. You're getting sound advice here, even though a welder might not have thought about SCUBA and SCBA.

Pulling a vacuum is not an "every time" thing for your purpose, so long as you don't let the bottle get empty and forget to close the valve. It's still required on occasion, as even the driest argon has some moisture in it and it will slowly accumulate.

Slow transfer is very important. Significant pressure changes produce significant temperature changes. At a properly metered rate, the water bath is not needed, patience is.

I have small diameter transfer hoses at work, with the appropriate CGA fittings each end. These hoses are rated for 3000 psi, minimum, since bottles can be certified for 10% overpressure, which is (IIRC) 2640 psi. I thread and tighten to the donor bottle, and hand-tight the recipient. I then crack the valve on the donor, and close it. This purges the transfer hose of all atmosphere and much moisture. I then tighten at the recipient bottle, and open it's valve fully. I transfer by cracking the donor bottle's valve, and walk away for a while.

Even done slowly, you'll find the transfer hose to be quite cold.

Steve S