Anyone tried filling empty CO2 cylinders with liquid CO2? (Vulcan mind meld style)

Discussion in 'Sand Casting' started by Mark's castings, Nov 7, 2019.

  1. Has anyone direct experience with transferring liquid carbon dioxide from one cylinder to another?. I'd like to transfer the contents of a 6Kg cylinder to another one. I understand the source cylinder is upside down and uphill of the receiving cylinder and you connect the two valves with suitable high pressure line of 1000 PSI working pressure and open both valves. What I'd like to know: does the liquid CO2 just run downhill into the receiving cylinder to get a full transfer of the liquid gas?.

    I've made some custom fittings for the Australia only "Type 30" food grade CO2 fittings: 0.860" 14 TPI to adapt to 1/4" tube 20 TPI brass 45 degree flare fittings and I plan to use 1/4" soft copper tube which has a working pressure of about 1900 PSI (CO2 is about 850-1000 PSI).

    The plan is to have the receiver cylinder out of sight around a concrete wall with the valve open and crack open the source cylinder valve.
    Last edited: Nov 7, 2019
  2. OMM

    OMM Silver Banner Member

    I have watched them fill my nitrogen tanks in a very similar manner. But I don’t know what other safeguards they have implemented or pump. My LP is filled the same way with a small pump... I am guessing you won’t get all of it, but you will get the liquid.
  3. Hi Matt, on an impulse I rang a scuba shop and asked if they could pressure test a CO2 cylinder: once there at the shop they took one look at the design and said while they could take my money, it would fail the test. It turned out to be a 1980's vintage cylinder of an aluminium alloy that develops fine stress cracks around the swaged neck and would no longer be gas tight. The cylinder had been full to begin with and lost gas over five years of sitting, it was due for re testing in 2009.
    Last edited: Nov 9, 2019
  4. Melterskelter

    Melterskelter Silver

    That cracking potential is just plain scary. It sounds like you prudently made a phone call that might have saved you from potential disaster. I have not and would not try the sort of transfer you describe. But after reading here about the known potential for some aluminum tanks to develop cracks, I really would not try it. I am glad you reported on this. It is good for me to be reminded of the amount of energy stored in compressed and liquid gases and the potential for its instantaneous release. Ouch!

  5. Petee716

    Petee716 Silver Banner Member

    Tank integrity aside, wouldn't the flow just stop once the pressure between the two tanks equalize?

  6. Peedee

    Peedee Silver

    I have to agree with Denis, re-filling tanks makes me want to take a step back to think about it, not to say it can't be done.

    As for the physics unless one tank is higher pressure than the other then a pump would be needed as mentioned above. (I think)
  7. It was a bit too risky the more I thought about it, I found a source of new steel 6Kg cylinders for $85 AUD, it just remains to find out how to ship it as "dangerous goods".

    These Australian made 1980's vintage aluminium cylinders with the problem can be spotted by the valve body having a tapered thread according to the scuba tank guy who identified it from across the room. I spoke to Peter my foundry mentor, he said they were 601 alloy and like aeroplane propellors, the castings are a gummy to machine alloy more suited to forgings. He said as the scrap aluminium gets hot enough to soften in the furnace there is some interesting separation of layers around the necks of the cylinders as if the metal de-laminates and is pressed together again in distinct layers during manufacture. The red brass valve bodies were also a source of cyanide like gas poisoning from the teflon seats being burnt.

    There are transfer refill kits sold online for filling up the soda stream CO2 cylinders and paintball cylinders. My local gas supplier charges extra for a CO2 cylinder with a siphon tube to take liquid CO2 from the bottom of the cylinder so it appears to be a legitimate refill technique although I don't know if equal sized cylinders will fully transfer the liquid CO2. I guess it somes down to the properties of the CO2 liquid and whether it will flow down a 1/4" tube and allow gas bubbles back up.

    As I understand the principle it will only be practical with gases in liquid form such as propane, CO2 and so on: you have to get the liquid to flow into the destination cylinder and maybe some gas back uphill to the source tank.

    Last edited: Nov 8, 2019
  8. I found a description of the issues with aluminium gas tanks: mine is an old pre 1990 CIG listed as being at risk, it also has a now banned tapered valve into a parallel thread neck. Even if it didn't have the tapered valve it's recommended to limit pressure to 600 PSI while liquid CO2 pressures are about 1070 PSI on a warm summer day.

  9. Peedee

    Peedee Silver

    I have a dislike for tapered threads, based on a fault we had on Piper landing gear hydraulic coupling (was overtightened by an engineer and cracked quite a time later).

    1000 psi is a lot of force to be playing with it's just how dramatic the failure is, split and vent or crap flying all over the place!
  10. That's the problem with planes, stuff has to work right every single time, whatever it's history. Better materials tend to be very slow to be adopted in aviation over materials with properties that are well known. I came so close to filling an aluminium with all the warning signs: the guy at the scuba tank shop asked me if the cylinder had been full and leaked the contents over time, which it had.
  11. Jason

    Jason Gold Banner Member

    That and the blood sucking attorneys start frothing at the mouth! You're lucky you had the right dude at the tank shop. Imagine if you had some wet behind the ears millennial punk too busy screwing with bookface to pay attention to the words coming out of your mouth!:eek: We had a guy come into the hanger yesterday telling us the FBO just fried his airplane. Dumbass line guy hooked up a 24vt external power cart to his 12volt airplane. I'm standing there at the plane with the line guy and pointed to the 12volt only placard on the very little door he had to open to connect the 24vt cart to. Can you say, Dumb looks are still free? :rolleyes:
  12. A lot of the rather complex 60's-80's vintage electronics communications gear I worked on had unique connectors internally to prevent such a mixup. I would have thought planes would have a dedicated 12V and 24V connectors to make it hard to do.
    Another CO2 cylinder update: I grabbed my old 6Kg extinguisher and shook it a few times, there was no detectable sloshing of liquid CO2 so I fired it and got a cloud of white spray that petered out almost immediately. The thing was almost empty and would have been useless if I had a fire to put out.
  13. Jason

    Jason Gold Banner Member

    If this isnt pretty obvious, I dont know what is.

  14. That's the thing, they went to the effort of making it a polarized plug but didn't make one pin fatter than the other for 12 volts and the other way round for 24 volts, in effect making it a detector test for dyslexic / illiterate line staff.
    I'd been wondering today what damage that plane has copped to the electrics, it's going to be expensive to repair but hopefully confined to the battery and a fuse or two and not something like instruments or radios. I see Piper
    planes have a specific 12 volt connector that is different to that NATO AN2551 28 volt connector.
  15. Jason

    Jason Gold Banner Member

    Oh yeah, the dreaded piper single pin. That thing has screwed me in the past.:rolleyes:

    Looks like it just has a couple of fat ass wires and that was it. I think the contactor might be screwed but wont know until we get power back on it tomorrow.
    Mark's castings likes this.

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