Transferring 75/25 from a large bottle to a smaller one?

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I have a small bottle on my cart that I use with my Millermatic 211.  I have a full size bottle sitting in the corner that I haven't used.  I came across a hose the other day that was made to connect the two bottles together.I know the bottles will level out if I hook them together.. but do I risk throwing the 75/25 percentages off by getting air in it over time by doing this?  The reason I would like to do this is to avoid having to run to the store when the small bottle runs out during a project.Thanks
Reply:You won't change the percentage as long as both cylinders start out with the same mix to begin with.Note however there are a few important things to keep in mind when trying to do this. Number one all the parts for this rig must be rated for high pressure. Home Depot fittings will grenade literally at the kinds of pressures that the rig will see even if the cylinder is only 1/4 full. At best most are only rated to maybe 250 psi, not 2000 psi. The cheap cast fittings will shatter throwing fragments everywhere just like a grenade, and you are standing at ground zero when you open the valve and let the HP gas in. High pressure fittings are not inexpensive and a basic set up can easily add up to almost $100+ in no time at all. Last time I added up all the parts for a 4' whip it came out pretty close to these numbers ( $30-45 in CGA fittings, $40-60 for the HP hose, and $15-30 for the HP fittings), and you still need some way to bleed down the lines when done to relieve the pressure to get the lines off ( the bleeder assembly's we used were $75-100 last I checked)...Number two you have to remember that cylinders equalize based on pressure, not volume. High pressure will drop fairly rapidly as you equalize the cylinders. If you had 2 282  cf cylinders and one was full the 2nd 100% empty,  they would equalize out the same. the 1st time at 1/2 full  and the 2nd time at 1/4 full. If one is a 282 cf cylinder ( full) and the 2nd is an 80cf cylinder (100% empty), The 1st fill would get you 65 cf in the 80 roughly when they equalize. The 2nd fill would get you roughly 45 cf in the 80 and the 3rd "fill" would get you about 36 cf, the 4th about 30 cf, the 5th about  23cf... So you get a 3/4 full 80, 2 half full 80's and maybe 3 1/4 full 80's for all the hassle and expense. There are uses for this, but over all it's not the most practical way to do this sort of thing. It works much better when you have several large cylinders and "cascade fill" starting the the cylinders with the lowest pressure and working up, but that means you need multiple large cylinders. It's not a bad way for someone who regularly runs large cylinders to "top off" say a small 20 cf cylinder they use occasionally. As soon as you get a new large "full" cylinder in, you top off the small one before it gets empty and then use up the rest of the gas from the large cylinder with the machine.Last NEVER try this with O2 unless you have had the training to work with HP O2 fills. Even a small bit of contaminant in the lines/valves can cause a fire/explosion. Even if everything stays clean, simply trying to fill too fast can cause the system to ignite from adiabatic compression and friction. EVERYTHING will burn in the presence of 100% O2 under the right conditions. You already have a fuel ( the lines/ valves etc) you have the O2, all you need is enough heat, and the ignition point of all materials drops dramatically as the O2 pressure goes up.I spent a lot of years transfilling cylinders and doing these calcs for fill volumes is one of those things I had to do daily. My numbers might not be exact this evening, but they are close enough to give you a good idea what to expect if you choose to go this route..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:is it possible to get contamination , moisture from humitdity or anything just from the fittings and lines alone?  shouldnt a 100% empty bottle be like 120% empty from the vacuum pulled on it in order to be clean.?        thermal arc 252i  -  millermatic 350P -   miller XMT, cp300ts, 30a 22a feeders, buttload of other millers, handfull of lincolns, couple of esabs  -   Hypertherm 1250 G3
Reply:Originally Posted by StainlessI have a small bottle on my cart that I use with my Millermatic 211.  I have a full size bottle sitting in the corner that I haven't used.  I came across a hose the other day that was made to connect the two bottles together.I know the bottles will level out if I hook them together.. but do I risk throwing the 75/25 percentages off by getting air in it over time by doing this?  The reason I would like to do this is to avoid having to run to the store when the small bottle runs out during a project.Thanks
Reply:Originally Posted by dave powelsonI trans-fill with HP set for inert gas mix. I won't discuss the parts used, etc.-here, since too manyyahoo's will figure they know how to mess with HP---on the cheap and have zip clues as to whatthey're messin' with.
Reply:A transfill system can be purchased complete at BR welding supply. Building your own without having any experience is very dangerous. This is the one I bought and works perfectly.http://www.brweldingsupplies.com/sho...r-kit-td-1.cfmWeld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:A lot of great knowledge and experience in the replies.  ThanksSounds like too much trouble for me.  Here is the hose I was referring to with different ends on it right now.https://www.weldingweb.com/images/editor/attach.gif Attached Images
Reply:I bought a "jumper" made of all copper from the LWS back in the early 80s,  It had both fittings and a 2 or 3 foot line.   I used it to fill a 20 cf bottle from a bigger one for jobs on the road.   It workes fine.   My LWS now said "dont' forget a 320 CF bottle comes at up to 2700 PSI.   The smaller tanks 80 cf and down are only built and tested for 2200 psi.I use it occasionally.DavidReal world weldin.  When I grow up I want to be a tig weldor.