Thats another daft thing to do because you don't know how much of the liquid you are getting into the one being filled. You need to invert the supply cylinder then fill the reception cylinder with a U bend in the supply hose while it sits on a set of scales until you get the right amount. Then that doesn't work very well with the consumer bottles because they have a spear to try and stop the liquid getting out the valve because the valve seals arn't designed to handle liquid hydrocarbons.
And even then if you have opened the recieving cylinder and air has got into it or you haven't flushed out you lines. As you fill it you may get a bang when the partial pressure of the O2 in the receptical goes up to high enough level to flash burn. This might not occur until the cylinder has sat in the sun a bit or been stuck in the back of your car for a period.
They arn't filled to the top maybe only half full and then if you fill it then throw it in the back of the car it will then heat up and there will be no room for expansion. I think they are rated up to 20 bar at 50 deg C if there isn't enough volume to compress sitting ontop of the liquid its quite easy for them to explode (not in the burning way but like a balloon)
All the ratings are lots of 2's from memory
Last edited by mad_jock; 11th Jun 2012 at 08:41.