I eventually gave up on getting the 6000 PSI cylinders (and then replacing/trading them as they got down to 4200 which I considered too low to fill from) and went with an adapter to the intake filter housing that converts my 4500 PSI compressor to take gas from regular 2300 PSI welding N2 gas through a standard purge regulator. Keep the output / flow of the purge regulator at 1 atmosphere into the compressor, the compressor doesn't know the difference,
You could even use duct tape to seal the low pressure N2 hose to the intake of the compressor and then put the compressed N2 into you 4500 PSI tanks.
Note that I am doing the same thing with Helium, using welding supply tanks and a purge regulator through my compressor to my SCBA 4500 tanks,
The nice thing is, I use down to 100 PSI out of the welding supply tank, no wasted gas left in the tank when I return it, it all was compressed to 4500 ans is usable in my air rifles.
You could then just buy your low pressure nitrogen bottle outright. Refills are cheap.
Well, it's a nice theory but then reality comes along and crushes it.
Used to be in the Houston region when you brought your empty owner tank to a gas supplier (usually a welding shop but back then Linde had a gas plant in Freeport that would fill cylinders too) they would use a Cascade system and refill you bottle either while you wanted or by the next day pickup.
BUT about 10 years ago all the welding supply shops and the big commercial outfits STOPPED doing on site fills. I was told it was due to insurance regulations at my usual supply the first time it happened to me.
What everyone wanted you to do was swap bottles... Now I had paid for new bottles and had doubts about giving them up for bottles of unknown hydro date AND my proof of ownership would disappear as they were not going to give me anything to prove the replacement bottles were mine. They said I would not be charged a rental fee, just swap bottles each time and pay for the gas. This might sound good but what if those people leave the company or it changes hands? And no one remembers the arrangement? If you ever do this GET PAPERWORK that you will own whatever bottles you end up with but I sure don't know how you do that!!!!!
I know this is a problem because it happened to me years ago. I had bought bottles from a company and a few years later they went bankrupt. I had moved to another state in the meantime and one time I brought my bottles in to get filled and the store employee noticed the ID / name on the necks and confiscated my bottles as 'belonging to that bankrupt company' as per DOT orders.
Since I had five bottles confiscated you can be F'n sure I tried to fight, I got my ownership purchase papers out of my files as proof and even took them to small claims court but lost anyway as my bottles were listed in Federal bankruptcy as that companies property on their master property list and that overrides my "worthless" receipts. Some GD clerks had never updated the lists or something or the lawyers used the wrong list, it doesn't matter because what it taught me is that unless you have a 'smooth neck' bottle it's never totally yours.
On the 6000 PSI bottles, I was amazed that no one carried them on my side of MAJOR INDUSTRIAL CITY Houston, they'd have to be special ordered each time and the waiting time was weeks! Mind boggling for that to be the case because generally ANYTHING is available in Houston (from the robes of a Congressman to the Congressman inside, so to speak, haha). Much easier to just get a std N2 purge gas bottle at the welding supply, go home and pump/transfer it to my tanks and then return it.
Another experience people are having is sending their bottles off to be hydroed and not getting the same bottles back. I happen to have a relationship with an aircraft service center that does speciaty hydros and I'm still getting my bottles done there BUT others locally have gotten ratty bottles back instead of their nice ones and the big industrial hydro companies did not have a clue where their bottles went. They got a bottle in and sent a fresh hydroed bottle back and are no longer set up to keep track of any one bottle amongst the thousands on their loading dock. Welcome to the future.
