Help! > Specific Engine Help
4 cyl. steam engine
crueby:
Gotcha! That helps my understanding a lot.
Okay, that looks like it will give you a balanced thrust from each of the pistons in each direction, which is good. The crank itself will be unbalanced for mass unless you have counterweights on each web, since one of the webs will be closer between two of the others. The counterbalanced webs were common, and should look good.
Charles Lamont:
Another interesting 4-cylinder loco with eight beats per revolution was the experimental 0-6-0 designed by Hookham for the North Staffordshire railway. It was intended to provide rapid acceleration for commuter traffic with closely spaced stations and steep gradients.
There is no way to make an intrinsically balanced crankshaft for this arrangement. If you put the cranks 1, 2, 3, 4 at 0, 90, 135, 225 it will sequence 1T, 3B, 2B, 4T, 1B, 3T, 2T, 4B which seems to me reasonably well distributed.
If balance is important, perhaps you should go for a straight six!
(Or three, of course).
paul gough:
Helo Chris, Glad I got my meaning across. Charles thank you for your mention of the Hookham loco, I was not aware of it and will certainly look for some information on it. If you have a couple of references handy that would be most helpful.
As to the balacing, it was primarily to do with power application to the shaft and thus the admission sequencing which you have indicated. I had thought if there was any advise on it pointing towards better balancing due to this then I could re-arrange things by inter-changing the crank settings of particular cylinders. I am inclined to go with your assessment of it being "reasonably well distributed". I am probably 'over-thinking' the issue but was curious about it. Again, thank you for your input.
crueby:
Unless you are going to run at very high speed or build it very large the balance should be fine!
paul gough:
Hi Chris, This engine is to provide something of an experimental platform. Initially it will be for comparing a reversable in-line 4 cylinder oscilating engine with 90 degree crank setting to one with 135 degree crank setting in terms of its behaviour. The first iteration will likely be as a low pressure, low speed engine, e.g. 2 to 3 bar and 40 rpm approx. This reflects the sort of operation of a full size engine of this type. Partly the 4 cylinders and 135 degree crank setting is to provide improved self starting and hopefully less vibration. I am also interested to discover what the steam demand and therefore size boiler is optimal under these output conditions. The second iteration is to split the engine in two and place them together (side by side) and integrate their output through gear drive, again comparing 90 and 135 crank settings. The third itteration after determining which arrangement is better, my intention is to explore the highest pressure and speed (rpm) this engine can deliver at a level that could be sustained without detrimental effects. Finally, I may proceed with a test to see just how far one can push this type with pressure and speed up to and including some sort of failure, which I expect will be in the trunnion retainer and seals area. To be sure, a rather lengthy exploration, though this is the sort of thing that interests me now. Regards, Paul Gough.
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