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>I am so fed up with the problems of getting a mix fill round here (NW >England) >that I'm going to have to do it myself. Helium cylinders here (from British >Oxygen anyway) only have a 137 bar (2000 psi) fill pressure, so even >cascaded, >you're going to loose a lot. My question is this: > >Is there any reason why the outlet from a helium cylinder (appropriately >regulated, restricted etc. to approx 1 bar of course) shouldn't be >directly fed >into a compressor inlet to be compressed into the scuba cylinders just >like air? >That way you could drain the helium cylinder practically dry with little >more >than standard gear. I'm not talking about a lash-up here, proper regulator, >hoses, inlet gauge, seals etc. for safety & to ensure no air inadvertently >gets >sucked in. I'm guessing that some sort of 1 bar reservoir is going to be >needed >to smooth out the compressor's first stage inlet pressure variations, but I >can't see too many other major problems (apart from - if it such a good >idea, >why doesn't everybody do it) > >This should be a simple yes or no question and I'm not really interested in >anyone's "opinion" about it, so if you don't know what you're talking about, >please don't bother to reply. But if you do, and especially if you know of >commercially available gear or published information, I'd appreciate it. I can pass on the following personal experience: 1. I have 4 He tanks (330cu.ft) in my cascade system and the lowest tank is really low by refill time. Not much wasted gas. 2. I have my own RIX SA-6 oil free compressor and tried to regulate (with a standard scuba) regulator from some single 120 HP tanks into the compressor and then into another set of "doubles" so as not to "waste" the trimix. What a pain in the butt; took the entire day, almost blew out the diapghram of the regulator. Tried manual regulation and had too much waste. The problem is that the intake pressure has to remain at 1ATA while the cu.ft per minute rate of the compressor changes as the pressure builds. Used a vacumn guage to regulate this, but overall the waste of time wasn't worth the savings in the gas. Bottom line: Throw out gas that you don't use, don't mix until you're ready to dive in the next few days and use a cascade system as Rich Pyle described. Harold H. Gartner III 6900 Via Alba Camarillo, California 93012 home: (805) 482-9743 home fax: (805) 987-6804 office: (213) 487-6240
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