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Hi Gary, while you are thinking about silver soldering, I will make a few comments on the overall project.It is important to separate the ideas of flash steam and high speed engines. Of course, the two are often associated in a project, and for quite valid reasons, but it is not necessarily so.A flash steam boiler, sometimes called a mono tube boiler, is a boiler configuration that provides a quite large heat transfer area for steam raising, with quite low weight for the steam production achieved. But at the end of the day, the amount of steam raised is determined mostly by the burner, and how much fuel can be burned, so long as you have enough heat transfer area. I was tempted to include the word efficiently in that sentence, but not all projects are interested in efficiency. If someone wants to break a record, they want maximum power, and if burning more fuel, even less efficiently, achieves more power, then they go for it.Part of the low weight is achieved at the expense of water capacity. There is effectively no water storage in a flash boiler, so they can’t be operated like my little boilers by filling up with water then lighting the burner and start steam production. Well perhaps they could, but it would be a quite short run. They really need a feed pump, preferably driven by the engine, but again it is not the only way. The preference is because both steam consumption and water requirement, the same thing really, are dependent on engine speed, so while it is still not easy to balance the two, it is easier than if a separate pump is used.Of course, the high power to weight ratio is very desirable for high speed vehicles, whether land based or water, and when combined with a very big burner, can produce awesome power to drive the engine.But it does not have to be so. If you use a quite moderate burner then you produce only the proportionate amount of steam. You could build a quite moderate steam plant for a model boat for very sedate performance. This approach has its own chapter in Benson and Rayman’s excellent book, even though the rest of the book is a fascinating look into the world of high speed hydroplanes. I think I remember you buying it, so you will be aware of the valuable information there.In addition, it is not necessary for there to be no water storage. A moderate plant can include a pressurised water tank, with an air cushion over the water, between the water pump and the steam coil. It will smooth out the flow and give a bit of a safety factor against water failures, which might allow you to bring a model back to extinguish the burner. A separate tank like this can allow design of the plant with a much lower centre of gravity than a more conventional boiler design, which is good for stability of a model boat. Of course the fire tube marine boiler also has a good low centre of gravity.The engine is a quite separate issue. An oscillating engine as you have already built can operate quite slowly when required, particularly a twin cylinder double acting design which does not have the dead spots that the flywheel must supply the energy to carry through. Similarly a slide valve engine, or any of the other designs we usually see on this site. The upper speeds are mostly limited by the quality of balancing achieved, not easy with heavy reciprocating parts. My mill engine achieves around 2000 rpm unloaded with quite low steam pressure, with limited balancing, but I suspect that even at this speed, wear might become an issue if I pushed it that fast for long. So hardened pins and more attention to bearings might be required.Slow engines are generally characterised by long stroke compared with the bore, though not necessarily so. More significantly the steam is admitted mostly after the top dead centre, even when a little is admitted before. Your engine with the inlet valve operated by a peg on top of the cylinder has the steam admitted equally each side of top dead centre. (I wonder how a double acting engine would be implemented). More likely a twin single acting, or better still a three or more cylinder configuration with the cranks spaced equally around the shaft. Because of this necessarily early admission, the engine needs to get enough of a kick every steam admission to accelerate the flywheel to store the energy necessary to push the piston over the next top dead centre position. Otherwise the engine might just oscillate back and forth through about 340 - 350 degrees. The engine will be happier going faster for this reason, but it still does not require the extreme speed sought by the racing community, it just won’t run slowly like your little oscillator. But a quite interesting design, well worth trying.So while roaring blowlamps, extreme pressure and temperature steam conditions, and high speed racing hydroplanes, are typically based of a flash boiler, uniflow engines, and very highly developed material selection, and manufacturing techniques, there is no reason why you cannot run your simple flash plant with a more moderate burner and your current engine, which might run quite happily around 1500 - 2500 rpm (at a wild guess) but definitely not slow like your oscillator. Mind you, an oscillator is also is no slouch if you give it enough steam, as the oscillating engine design involves a much smaller oscillating mass than a typical mill engine, in both reciprocating and rotary motions. Mine go at 2000 rpm measured with a digital tacho when unrestrained and with only the little meths burner, and are really not fussed at this speed. Much less vibration than the mill engine.It is one of those things that has to be tried, but if you can tackle a little engine driven pump, perhaps with bought gears, there is no reason that you could not try your flash plant with this new engine. Keep the burner relatively gentle until you get the feel of it. But I really would not recommend the flash plant with a hand pump only, unless you have plenty of water capacity. It all comes back to heat balance.By the way, stamp collecting is only allowed during the current lockdown situation, and there is another current thread where that can be included. In the mean time you have an an engine and flash boiler to complete!MJM460
you have a cast-iron cylinder then the material to use is cast iron .