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Steam Stationary Engines, Traction Engines

Stevenson Links


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Old 12-19-2012, 08:20:08 PM
Rob Bryce Rob Bryce is offline
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Default Stevenson Links

Hello,

I've asked around to find out if you get more power (or economy) when crossing your rods on your Stevenson link valvetrain, or if you get more power (or economy) when you run them straight.

I've received 3 different opinions.

So I thought it'd be an interesting topic here! What is the general consensus?

--Rob
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Old 12-19-2012, 09:03:42 PM
Joseph Graziana Joseph Graziana is offline
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Default Re: Stevenson Links

If the valve opening is the same their will be no diffrence if it changes travel distance then their will be a change.
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Old 12-19-2012, 09:33:30 PM
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16GaarScott 16GaarScott is offline
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Default Re: Stevenson Links

Rob, "Audels Engineers and Mechanics Guide 1" by Frank Duncan Graham has a very good explanation of the link mechanism. Actually, the whole book is good for reading about steam engines. The slide valve, valve gears, governors etc. are covered. Written very well and easy to follow.

On pages 322-326, crossed vs. open rods, is covered in detail.

You can read it online or download a pdf file at

http://openlibrary.org/books/OL70527...hanics_Guide_1

If this link doesn't work do a search on openlibrary. org and it should come up.

I was fortunate to find an original (but well-used) on ebay recently. I think there are reprints out there also. Steve
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Old 12-19-2012, 10:22:16 PM
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Gary K Gary K is offline
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Default Re: Stevenson Links

Open Rods and Crossed Rods. In considering this question, the eccentrics are supposed to point toward the link when the engine is on dead centre, regardless of where the crank may be. In Fig. 236 the rods appear to be crossed, but a little consideration will show that when the crank is turned to the opposite centre the eccentrics will point toward the link and the rods will be open.

Effect of Open or Crossed Rods on Lead. “Hooking up,” or moving the reverse lever toward the centre notch, increases the lead when open rods are used, and decreases the lead with crossed rods.

Putting the reverse lever in the middle notch will stop an engine having crossed rods, but with open rods there is always some port opening even in mid gear and the engine will not stop unless it is loaded.

Courtesy of CLARKE SCHOOL OF TRACTION ENGINEERING





An interesting and very useful feature of the Stephenson valve gear is that with “open” eccentric rods, the lead increases towards mid-gear. This is due to the angularity of the rods and the effect is greater the shorter the eccentric rods. If “crossed” eccentric rods are used, the lead would decrease towards mid-gear, an undesirable feature in railway locomotive.

Courtesy of LOCOMOTIVE VALVE GEARS


Gary K

---------- Post added at 09:22 PM ---------- Previous post was at 08:44 PM ----------

Figs. 236 and 237 show open rods, and Figs. 238 and 239 show crossed rods.




Gary K
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Old 12-21-2012, 12:54:13 AM
GreasyIron GreasyIron is offline
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Default Re: Stevenson Links

Quote:
Originally Posted by 16GaarScott View Post

You can read it online or download a pdf file at

http://openlibrary.org/books/OL70527...hanics_Guide_1

Steve
Link worked great. I merely skimmed over the topic at hand, but it looks like there is a ton of information throughout - I'll have to read it through some day.
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