We had a brand new 27.5Kva generator delivered and the man in charge could not wait to start it up.
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This genny is air start but of course it had no air in the tank until it had been started. It was started with the attached starting handle and the air pump engaged and then when 600lb was in the tank the engine was switched down. Later it was started up again using the air start motor which made a funny noise but no one took notice. At that point I started a service of the machine and found no oil in the air start motor. Decided to strip it and found one piston with a broken ring so decided to make another as there was no chance of spares.
I found one of those racking base stands and gave it a rub with a file and it seemed soft enough so turned up a new ring and split it and heated it up and then put it on the piston and re-assembled the motor. Remembering to put oil in as well ! Started up again with no funny noise and as far as I know still going strong.
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clive
Hello Rob,
What steam pressure are you operating at?
Do you have an estimate of the superheat?
I agree with Tom G that cast iron rings on cast iron cylinders is the traditional method.
In today's world, other metals like steel or brass might also be possible.
Teflon might be an option if the pressure and temp are not too high.
My experience with Teflon O rings in hot oil piping flanges is that 500 F is the upper limit. This was with the O rings captive in grooves. In a sliding seal situation, the limit is probably lower. One issue is that Teflon starts to distort around 500F. When you remove the seal after exposure to high temp, you probably will not be able to re-install the seal.
Not sure where one would find the proper size CI rings except to make them.
I am told that back in the 's mechanical engineering students were required to take fairly extensive machine shop classes.
At the U of Minnesota, one of the projects they did was to fabricate new piston rings for a Ford Model T engine using cast iron sewer pipe as the source material.
I dunno - could work, but I am not sure how one would go about it.
If you run iron on iron, you will need cylinder lubrication. Maybe you already have this. Cast iron is usually porous enough (due to the carbon flakes) that it holds oil well and does a good job of polishing itself when running against an iron cylinder. For a small model engine, a "pressure pot" feeder on the steam line, holding a few drops of oil, is probably enough. You have to periodically refresh the oil charge because under the heat of the steam, the oil is slowly emulsified and carried away with the exhaust steam.
Another item that you probably know: Traditional steam engine design has a slight relief in the cylinder bore at top and bottom center. The relief only needs to be 0.010" or so on the radius. The idea is that the outer ring slightly overruns the relief with each stroke, and thereby does not generate a ridge on the cylinder. The usual overrun of the ring is about 20% of the ring width. Without the relief, steam engines can really get to pound as wear accumulates in the crank and cross-head bearings. (I guess the Teflon rings would not need a relief). If you decide to install CI rings (or other metal rings), you might want to think about boring in a relief at each end of the cylinder.
Post some pics if you get a chance.
I would be interested to see the engine.
Regards,
Terry S.