# sliding rod eccentric



## Kermit (Jan 13, 2009)

I'm not even sure the name eccentric can be applied to this mechanism.








Has anyone used such a set up to operate a slide valve? The book I got this from was on the Kinematics of solid bodies, not exactly a steam engine topic but the author made reference to locomotives in his explaination - most of which I didn't follow very well.



Kermit


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## Philjoe5 (Jan 13, 2009)

Kermit,
That looks like a conventional eccentric - eccentric strap set up. The eccentric has its center offset from the crank center, and the strap has a rod connected to it to give the oscillating horizontal motion. This pic may help ???






Cheers,
Phil


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## deverett (Jan 13, 2009)

It is what is known as Hackworth's Valve Gear and was used on a few classes of British (and perhap other) narrow gauge locomotives in the 19th Century.

It was not particularly steam efficient, especially on the rough narrow gauge railways, but was easy to erect by the small companies that built this type of loco.

Some pictures of 5" gauge locos built with Hackworth gear can be seen at 

http://www.blackgates.co.uk/body_sweet_pea.html

Dave
The Emerald Isle


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## Kermit (Jan 13, 2009)

Thanks! The name "Hackworth" was what I needed . Got me lots of google returns with that one.


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## Captain Jerry (Jan 13, 2009)

If you are interested in valve gear design, you should visit http://www.tcsn.net/charlied/ and download the software. Although written for DOS, it runs fine on my Vista Laptop. 

Not only does it provide full motion animation of many valve gear designs, it allows you to slow the speed, stop at any position, it allows you to fiddle with the ALL of the parameters, including port dimensions, rod lengths, frame dimension, valve timing, etc. Of course you have to keep things real. If you make the con rod longer, you also have to move the cylinder a corresponding distance. You can change the eccentric throw and observe what that does to timing. you can use the dimensions to validate your own designs and the software will produce accurate of charts of valve open/close and a lot of other variables that you might want.

You have to download about 15 files and decompress and set them up but there is a control program that lets you select you choice of mechanism from a chart. Really good stuff.

Jerry


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## ChooChooMike (Jan 13, 2009)

Definitely download that software (free). It's fun just to try out the different valve types, vary the parameters, etc. The animations reflect the parameter changes too !

Recommended 

Mike


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## Kermit (Jan 15, 2009)

This is NOT like a regular eccentric. The offset rotational axis causes more time to be used, as referenced to the crank, for the slide valve mechanism to move one direction than the other. In the picture I have above the difference is almost 2 to 1. Or at 60 RPM it takes 660 milliseconds to go from right to left and only 340 milliseconds to go from left to right.

That should have allowed, with proper selection of offset, for a much better timed slide valve operation and therefore more economical operation of the steam engine its attached to. Right?


Keeping myself confused to avoid comprehension,
Kermit


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## Kermit (Jan 17, 2009)

I made a complete diagram of one rotation of the crank. This one shows a 3 to 1 time differential. Definately not a simple strap on eccentric where timing is concerned. SO, (needle pulling thread?) What to do with such information...

Maybe I'll build it. It seems simple enough machining for a true noob to perform and have a smallish percentage chance of success. 

I give thanks to the Finger Engine/Motor Thread for this idea.

Keeping myself entertained is sew easy, 
Kermit


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## Philjoe5 (Jan 17, 2009)

Ah the light comes on - now I see it. The eccentric pivot slides, therefore, is not fixed. And that gives different +x, -x distances. I'll have to add this to my collection of mechanical movements. Thanks Kermit for asking the question

Cheers,
Phil


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