Author Topic: My scaled down version of the steam traction engine "Minnie"  (Read 1332 times)

Offline ddmckee54

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #15 on: March 19, 2019, 04:03:48 PM »
2 speed transmission in the works?  You've really nailed the sprinting speed, now you need a comfortable walking speed option.

Don

Offline Kim

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #16 on: March 19, 2019, 05:31:08 PM »
It runs well!  It seems that these little traction engines all run fast, but you seem to have it handled :)
Congratulations on running it under its own power!  That's a great accomplishment!
Kim

Offline ChuckKey

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #17 on: March 20, 2019, 01:40:57 AM »
Does it not have a regulator (throttle) valve?

Offline MJM460

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #18 on: March 20, 2019, 09:20:10 AM »
Hi Zephyrin, congratulations on getting it running on steam, a great achievement, to be pleased with it is somewhat of an understatement, I would be delighted, or over the moon.

A few posts back, if I understood correctly, you can run it forwards on air by pulling it backward when in gear, so compressing air in the boiler?  Even more impressive.  You are surely a master at these small machines.

 MJM460

The more I learn, the more I find that I still have to learn!

Offline Zephyrin

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #19 on: March 20, 2019, 09:55:24 AM »
thanks for the comments, very appreciated !
as everyone has noted, my tractor runs much too fast...even at low gear as in the video!

Yes, it do have a regulator, a sliding valve like its larger model, but not as convenient as the needle valve I put on my G1 locos...
the other point is that as soon as I stop the tractor, the idle engine speed raises to tremendous level, and risky for all these little parts, so I closes the regulator, and steam pressure get higher...making the re-start more difficult.
I clearly need a convenient way to regulate the burner.
but, as I know it works, more probably I will leave it as it is on a shelve, with a few paint touch-up...

MJM, yes, pulling it backward raises air pressure in the boiler...
I put a small spring on the steam valve to keep it tight on the port face, hence the engine becomes reversible.
Adiabatic processes I assume, but I have no way to determine precisely changes in pressure and temperature of the air !

Offline MJM460

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #20 on: March 20, 2019, 10:44:13 AM »
Hi Zephyrin, I suspect the little spring is the secret to holding the slide valve against the face to get the air compression started, however, as soon as the air pressure starts building in the boiler, the air pressure will hold the valve against the face, just as when running as an engine.

Compression in a reciprocating compressor is approximately adiabatic as you suggest, just as the expansion when running as an engine is approximately adiabatic.  If you had a pressure gauge on the boiler, it would show the pressure, just as it does for steam, but I guess a gauge would be a bit impractical on such a small machine.  At least it would look out of scale.  The temperature of the air will increase on compression, but the boiler surface area will help it cool back to atmospheric temperature.  You can demonstrate this with a bike pump if you put your thumb over the outlet and push in the handle to compress the air trapped in the pump.  And of course we all know how hot the cylinder of our air compressor can get.

Also interesting problem, how to control such a small plant.  As you say, if you just throttle the steam, you have not decreased the energy input, so the pressure just rises.  Throttling alone is a short term control measure.  However, I wonder if that slide regulator would be easier to use if it had a screw actuator so you could make quite small movements to find a position where forward speed on load and unloaded speed in neutral we’re both acceptable.  But nothing needed on the shelf, just things to ponder for the next model.

I think that machine deserves a place of pride on the shelf.  It is a great tribute to your skill, both as an engine and as a compressor.

MJM460

The more I learn, the more I find that I still have to learn!

Offline b.lindsey

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #21 on: March 20, 2019, 12:56:17 PM »
Thanks for the latest video. Quite an amazing little engine and just a beautiful restoration job all the way around!!

Bill

Offline Zephyrin

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Re: My scaled down version of the steam traction engine "Minnie"
« Reply #22 on: March 21, 2019, 09:51:33 AM »
Thanks for these kind words...
the point is that as soon as the tractor is running, it reaches lawn or flower pots before I have time to turn steering wheel, set the regulator, the butane valve, the gears, the brake, and the whistle too ! I have to move for a much larger plot !