David Weinshenker wrote: > > > Seems like the best way is going to be to have some 6000 psi bottles > and a valve manifold, and cascade-load the flight pressurant: Start by > filling the flight tank from bottle #1... for the first several fills, > that will get it up to 4500 psi; once bottle #1 drops below 4500 psi, > bottle #2 can be used to top it up. When bottle #1 gets empty, have it > refilled to 6000 psi and use it for #2, and move the former bottle #2 > to the #1 station to use the rest of the gas in it. (Since the flight tank > will be much smaller than the source bottles, if #1 starts at 6000 psi > then the flight tank can be filled from it a number of times before its > pressure drops below 4500 psi and some gas must be taken from #2.)
For the Really Cheap among us, you do your cascade load in as many steps as you have supply bottles, equalizing to the lowest bottle first, then the second lowest, on up to the highest or until you reach target pressure. I often have 3-4 bottles which I tap in turn for the EZ-Rocket. For your application, one 2600 and one 6000 bottle will do for many fills- your flight bottle is what, a liter or so at 4500? A 37 liter DOT3AA6000 bottle will go a long ways when used just to take it up from the lower pressure, not from scratch. > For vehicles in the KISS/Spike category, it's going to be some while > before our flight rate is so intensive that we'll need anything more > than such a setup - which we may well be able to manifest for less tha > the cost of a scuba compressor, and which will allow us to use commercial > gases of known quality. Perzackly- nitrogen is cheap and high purity. I use a compressor and suffer the woes of cleaning the output gas because helium isn't cheap, and I use so damn much of it. Filling the 45 liters of bottles on the plane takes about 80% of the content of a $160 6K bottle of helium. You betcha I recycle, but you guys are lucky enough not to need it. I don't know how difficult it is to get 6K rental nitrogen bottles, but if you guys are interested, XCOR can sell you a 6K bottle for $400. These cost $1500 new, $600 on the used market when you can get 'em. You could put your name & address on it then send it off to Praxair or Air Liquide to be filled, probably well under $100, and not have to pay rental fees for the rest of time. In my spreadsheet, I get about 22 cascade fills of a 1 liter flight bottle from a 45 liter 2500 psi bottle plus a 37 liter 6000 psi bottle before the 6k is under 4500 psi. -- Doug Jones, Rocket Plumber (perforce) _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
