Had a bit of fun turning my Jensen #65 into a very primitive tandem/cross compound with my PMR #3 mill engine:
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However due to the low pressure i was running at (around 15 PSI) it is not really very effective and the PMR had very little power and you can see it is running a lot slower. Still it was fun to experiment and i might try again using one of my Stuart's which has a 3/4" bore as the low pressure cylinder instead of the 1/2" bore that the PMR has. I guess if i wanted to be really adventurous i could try putting the Stuart off the PMR exhaust to make a triple but i foresee problems with condensation and water carry over and keeping everything hot.
I reckon someone could make a tandem or cross compound from Jensen parts since you could mate the 7/16" cylinder of the 65# with the 3/4" cylinder of the #20 and have and extended piston and valve rod going through both.
Anyway here is my video of the Jensen #65 & PMR #3 running together:
https://www.youtube.com/watch?v=X8ydHOPzO2k
Now that is rather cool there Philip.
I think the PMR 3 is running rather faster than I'd have expected considering that starting with such a low pressure going through the Jensen, there could be very little if any expansion left available in the steam feeding the PMR.
Nicely done that!
The PMR is running surprisingly well Phillip.
Now there's a fun little set up and "efficient run"
You sure are having fun, Philip...!!!
If you want to make it act like a true compound, you can have some fun by having an identical sized pulley on each engine and belt them together so they turn as one.
Gil
I must admit it was fun to experiment and it is a good demonstration of economy of steam and that there is still enough energy to turn another engine over. As has been pointed out they need to be coupled together to be a true compound and i will try what Gil suggested as both engines have similar sized pulleys, however due to the low pressure there is very little expansion going on and you would need over 60 PSI to notice any efficiency. I actually got both engines to run on as little as 7 PSI showing on the gauge in that setup.
I was thinking you could maybe modify a Jensen #55 to act as a cross compound by swapping out the engine units and fitting a #65 and #20 cylinder assembly, the main problem you would have is that the stroke difference of those two engines is 3mm so some modification/fabrication would be necessary.
Had a go with my Stuart 10V which also worked on around 12 PSI, although it did run slower than the PMR which i expected given the larger bore:
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Actually, if you only wanted to make the two engines run at closer to the same speed, at our toy steam temperatures and pressures, you'd likely get closer by reversing compound theory and feeding the larger bore engine with steam fresh from the boiler with the smaller bore then run off of its exhaust. Still be a rather serious mismatch I'm afraid.
Actually, if you only wanted to make the two engines run at closer to the same speed, at our toy steam temperatures and pressures, you'd likely get closer by reversing compound theory and feeding the larger bore engine with steam fresh from the boiler with the smaller bore then run off of its exhaust. Still be a rather serious mismatch I'm afraid.
That is good point Daniel, another thing that might have helped is an intermediate receiver between the two engines. One good thing with the Stuart is that it had drain cocks which made it much easier to warm through and clear the condensate.
Couldn't resist giving this a go with my most recent acquisition:
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What engine is that on the left? Very pretty
Is it a Microcosm?
nice little test run there Philip, I like it.
Ditto !
Thanks for sharing Philip.