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THE BASIC BOOSTER MODULE
The basic booster module consists of an appropriate hydraulic cylinder, cleaned and adapted for HP gas use, and plumbed using HP hoses and fittings, so it feeds from one tank and outputs to another. Check valves on the input and output lines to keep the gas moving in the right direction. Thereıs nothing special about the design. Itıs the same basic circuit youıll find inside any piston compression device, from a bicycle pump to a shop compressor. Operation is automatic. As the piston is cycled back and forth gas is alternately admitted in from the supply tank though the input check valve, compressed and driven out through the output check valve and on to the fill tank. Sounds easy, but the tricky part is finding a way to apply enough force to move the piston up and down. If one is boosting the gas to, say 3000 psi (200 bar) in a 2² (50mm) bore cylinder, itıll take a little over little short of 5 tons/4500 kg (3.14 x 3000 = 9420 psi) to do it.
Some people get nervous at the thought of using a hydraulic cylinder with compressed gas because of the fear that, since the cylinders normally operate with oil, some oil might find its way into the air. This isnıt a problem, if the cylinder is properly prepped - a hydraulic cylinder is physically no different that the cylinder on a Haskel or a compressor - itıs just a cylinder with a piston. Once it has been properly cleaned and dedicated for use with compressed gas, it is no more likely to attract contaminants than a ³real² booster. Two one-way check valves are used, and mounted to the cylinder port on both sides of a pipe tee, and hoses run from each check valve to a suitable yoke or other fitting to connect them to whatever tanks are going to be used.
Anyone experimenting with devices like this should be aware that, if one is flexible and creative, a lot of the stuff that is needed may be available from a scrap dealer or junkyard for a fraction of what it would cost new. Junkyards and scrap metal dealers tend to be hidden away out of sight, but there are more of them about than one might realize, and it can be well worth the effort to search one out.
For example, where I live, out in the country, I have two choices - a little scrapmetal yard in the next town, way off the main road, and a big metal recycling operation in the nearest city an hour away. The backwoods place haggles and often prices stuff by the item, mostly by whim, and the big recycler sells it by the pound - 50˘/lb for stainless, and 28˘/lb. for iron and steel (which includes junk machinery and hydraulics). The backwoods place tends to hold onto useful stuff almost forever, or at least until itıs sold or gets too rusty to sell. Thereıs a row of old buses full of such stuff, and if you dig around long enough you can often find what you need. The stuff moves fast at the big yard. Thereıs a back lot of huge machine tools and such, but basically they are in the business of turning old metal into scrap, not selling second hand machinery. If something looks interesting it gets stuck aside for a few days, but then it gets sent to the crusher if no one grabs it pretty soon.
To get the good deals there, youıve got to make it a regular stop, but when you do find something you need itıll be a bargain. I once asked the guy why there was so much machinery there that seemed perfectly usable. He explained that with the high cost of bringing in a tech work on the stuff, it was often cheaper for big companies to scrap the stuff and buy new every so often rather overhaul or even clean it.
That yard, I should mention, is an unusually friendly one for its size. Theyıll let a customer wander around, dig through the piles, and will usually stop whatever they are doing for a few seconds to try and remember if theyıve got what you are looking for. Thereıs also a cadre of regular customers, drifting in and out, and they can usually point the newcomer in the right direction. Other similar yards Iıve been to wonıt give you the time a day, and have no interest in selling piecemeal to the individual. So itıs often necessary to check out several scrap yards before finding a good one. Generally speaking, the smaller yards will be the easiest to deal with because the bookkeeping is less formal and the folks who run them rarely adverse to pocketing a little extra cash.
One thing to watch out for if shopping for a used cylinder for a booster is that a cylinder must be in pretty good shape to hold air - a beat up one that will work OK with fluid in it may be a real leaker on air. The key things are the condition of the bore and the rod. If either of these are pitted or scored the cylinder will leak or seal life will be drastically shortened. Unfortunately, thereıs no way to check the inside without pulling the thing apart, but the condition of the rod is usually a pretty good indication of the condition of the rest of the cylinder. However, if a cylinder has been left outside with the ports unsealed and water has gotten trapped inside the bore could easily be ruined while the rod is still perfect - especially because the rod is usually hard chromed, and resists corrosion, while the inside cylinder bore is bare steel. Note that if both sides of a double-acting cylinder are not going to be used the condition of the rod isnıt important. For most of the basic booster configurations only the condition of the bore matters, since the piston seal is doing all the work.
My booster is built almost entirely out of scrap parts. Both cylinders, the frame members, and the powerpack all came from the scrap yard, most of it at 28˘ a pound, and the rest haggled for on a per item basis. The hoses and check valves are new, and the other valves and fittings are a mix of new and used. You take your chances, of course. The first cylinder I bought looked great, but turned out the cylinder tube was badly corroded inside. Oh, well, Iıd only paid $10 for it. I bought another, for $15, that worked fine. Later, when I upgraded from the bottle jack and was looking for a larger cylinder to use as a drive, I found a pile of fairly clean cylinders that were all missing parts. One was a 3² version of the first one Iıd bought, but missing the rod. However, the rod appeared to be the same size as the one on the first cylinder, so I bought the incomplete one for $5 (with a little moaning to the guy about how the first one had been no good) and built one good one out of the two, leaving me with two good cylinders and a pile of spare parts, for a total of $30. This wasnıt as much a long shot as it might seem - one of the nice things about the tie rod cylinders is that thereıs a large, if unpredictable, degree of interchangeability between cylinders.
A little rooting about can turn up all sorts of other stuff, too. Some old blueprint machines that looked too new and office-y to be off any use turned out, on closer examination, to have HP SS QR fittings and gauges inside, as well as some lovely little 8 cf 3AA steel tanks, one of which Iım now using for an argon drysuit bottle.
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