I'm having trouble dealing with my usual O2 suppliers (long story), so if I attain some M tanks from a new supplier, i'm looking looking to take the O2 from a CGA-540 (M tank) to CGA-870 (E tank) and the quickly return the tank when empty.  My question is, will the pressure equalize once the PSI is equal in both tanks?

I bought a trans fill (CGA 540 3K psi) trans fill hose. When refilling M tanks starting at 2K psi in a welding T tank, the first M tank will stabilize at about 1.5K psi, the second M tank will end up about 1K psi stable. At this point, you can fill several E tanks off the welding T or K tank at 1K psi using a yolk adapter. This is how I cope, medicare won't cover my O2 when my blood O2 levels are fine. It's a shame they don't cover CH as a O2 tank necessity

PS, I tried that vitamin regiment Batch suggested and it was of no help or it made it worse, this is why I stay away from most of the homeopathic crap and keep my O2 supply up and ready for the impending doom that always comes to beckon.

Pain free wishes to all the CH sufferers out there, hang in there and happy holidays to you all.

Warning, you must be very careful when working the high pressure O2 valve and listen to it methodically, you don't want to get the O2 moving fast enough to go liquid (freeze) and blow out (freeze crack) the inner PTFE hose (no static electric build up issues with O2 like CO2). If you get transferring O2 too fast and you hear liquid O2 drops forming in the valve (popping) to the transfer hose, slow the hell down on the outlet valve and be patient! If you are not adaptive or knowledgeable about how to cylinder transfer into the gas manifold hookup at pressure, don't do it!

Let the hose temperature acclimate after the transfer, transferring O2 can can freeze the PTFE core in the braided stainless steel covered hose and leave it super stiff, and covered with ice, it gets that damn cold! Liquid O2 is far colder then liquid CO2 that instantly becomes dry ice at ambient air pressure, and supreme caution is of the utmost importance, like fueling a rocket tank properly!

I pay $33 for a 2K psi T size welding tank, there was a $185 10 year lease on the T tanks each and I have 2 of them so I always have one to return while I finish one off.

E tanks are 1,200 psi, M tanks and welding tanks are 2,000 psi, you wouldn't want to transfill an E tank from a M or larger tank until the M etc tank is below 1,200 psi or you may have a O2 bomb that kills you. That much O2 released at once will almost assuredly start an uncontrollable fire from the smallest spark source. Remember Grissom, White, and Chaffee from Apollo one! Do the transfill out in an open ventilated space, IE open garage.

The CGA 540 to CGA 540 tranfill hose was special order from weldingsupply.com , about $60 special order hose adapter with shipping cost included in the base price. (special order, NO return hose item)

The CGA 870 E tank to CGA 540 tank adapter is available on ebay for about $40 before the shipping costs. My medical O2 supplier charges $25 for an M tank and $15 per each E tank, thus why I refill them from a welding T or K size tank. Those medical suppliers suck for delivery time, I load My empty welding T tanks in my truck for transfer and avoid the delivery charges. Medical O2 is a rip off if you don't have health ins that covers the O2 costs. The M is not in the picture, but the medical M size tank is between the K and L size tank, and slightly larger then the Q size in the picture below.

As a military veteran, I could probably go to the VA for assistance. As an old soldier, I won't take $ from the VA when there are men my sons age in wheel chairs from IED's ETC. I'm too proud to burden my government for my CH. It's bad enough that I'm already on the SSI disability dole because of my CH.

Medical E tanks may be rated at 2K psi, but the crappy valves won't hold that pressure. The E tanks my medical provider supplies are 1200-1400 PSI and they rarely hold that pressure for more then a month. The E tank yolk valve sucks at holding pressure.

No matter what, I always have several M tanks charged up and the T tanks to bleed off. I don't know about Mark but I go through a crap load of O2 when I'm in bad head busting mode. No E tank will even come close to beating off my CH demon when I'm in torture mode. An E tank is nothing to me, I could just sit in the corner with a hot pack on my head and be better off by the time the pain runs it's 30 minute course. An E tank is dead at 15 LPM in no time like 10 minutes and I'm back to punching my blithering head. I got a prescription for lidocane from my Nero that you squirt up your nose on the HA side, it really helps a lot !!!

No matter what you do, those welding T tanks will save you from impending suicide. Been there like many and know what a KIP'er 8-10 for 2 hours feels like. Last month I went through 4 T tanks and now I'm back on the O2 every 2 hours all night long. I got lucky because my last medical O2 supplier abandoned 8 M and 6 E tanks, so I keep refilling them off the welding T tanks.

Like Mark in his link, I purchased a 2.5K PSI high flow welding regulator that is infinity adjustable on the output manifold. Those medical regulators suck because they can't push the O2 through a long supply line and fill the capture bag properly. My Med / aviation regulator only has 10-15-20 LPM on the high flow, it's too hard to find a point that's right without wasting O2. The welding regulator has a variable spin regulator that can be set to any output you desire to keep the accumulator bag full without wasting O2 from the bag. If you don't have a bag type O2 accumulator, one can be assembled with minimal parts from the local medical supplier. I tape a 1 gallon ziploc bag onto the flow plate valve and use a asthma inhaler mouth piece with the air slot taped off. Use the good 3M white electrical tape.

This breather apparatus has lasted me 10 years with a new bag every few years of use time. The masks are garbage if you have a weeping eye and your nose is running like a faucet.

This O2 regulator in the picture was $85 on amazon and the green O2 bayonet medical hose fitting adapter was $3 for a bag of 5.