walschaerts valve gear issues

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trainman154
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walschaerts valve gear issues

Post by trainman154 »

Hi I have a 7.25 inch gauge model locomotive that I am restoring( just a note that I am not the original builder of this locomotive). I pulled the valve out of the locomotive to lap it so that it would seal properly and that went all fine. The issue came when I went to reset the valve so that it was timed correctly. I could get it to be set correctly going in the forwards direction but going in the backwards direction the valve would only let steam go into one side of the cylinder which i am assuming will cause it to run rough.

Is there any way for me to fix this?

Thanks
318J
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Re: walschaerts valve gear issues

Post by 318J »

Rick Rowlands recently retimed the walshearts gear on his 2 foot gauge engine. He did a very thorough video explaining his process. Perhaps it may be of some sort of help?

https://m.youtube.com/watch?v=QbyAqckkN84
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jscarmozza
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Re: walschaerts valve gear issues

Post by jscarmozza »

Check out the locomotive animation at trumpetb.net, it helped me with a 1" pacific project that I am rebuilding. I had it running on air but started to adjust things and got it got it so screwed up that it wouldn't run at all. What I think I learned (please correct me if I'm wrong) is there is a difference in setting the gear with a D valve and piston valve, my project had a piston valve and setting the gear according to D valve specs didn't work, I reset the gear according to the referenced animation and got my project running again.
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Bill Shields
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Re: walschaerts valve gear issues

Post by Bill Shields »

Start at the cranks and work forward.

Any other way is counter productive.

If the cranks are not set right...you are just going in circles.
Too many things going on to bother listing them.
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AnthonyDuarte
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Re: walschaerts valve gear issues

Post by AnthonyDuarte »

Great video, but Bill is right. If the crank isn't set right the rest is pointless.

Full sized locomotives have their eccentrics keyed in place, so they're a fixed variable, but that's not the case on our models.

You can follow the same procedure outlined in the video. At front/rear dead centers, move the j-bar back and forth to check for movement in the valve stem. If there is any, adjust the crank (rather than the eccentric rod) until there is no movement in the valve. If you can't find a spot where there's no movement at both ends of the stroke, then there is an error in the eccentric rod. If there's miniscule movement but you're able to get it even on both front and back, you'll may be able to time the locomotive reasonably well but it is a compromise.

Anthony
VGC
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Re: walschaerts valve gear issues

Post by VGC »

I could offer a test if you can wait some time for the result:
Send me the valve piston positions in piston dead center position and the valve and piston position when steam inlet closing, each for forward and bakward riding, and I try to tell you what to change on your valve gear.
Online program for valve gear design:

ValveGear Constructor [EN]

Image

With automatic pre-optimization, DXF export, etc.
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Bill Shields
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Re: walschaerts valve gear issues

Post by Bill Shields »

All suggestions are assumptions that AT ONE TIME THE VG WAS CORRECT.

Cranks can slip on pins...pins can rotate in wheels..cranks can be the wrong length from day one..or have been put on wrong from day one....or all of the above.

Many locos are set up to run good in full forward and cut off/ reverse are left to where they fall
Too many things going on to bother listing them.
jscarmozza
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Re: walschaerts valve gear issues

Post by jscarmozza »

This was the criterion that I re-set the valve gear to, and it didn't work at all on my Pacific project. Oddly, this is the same method I used on my two LE Atlantics and they run beautifully, nice and square. So what's the answer? I had to turn the crank about 90 degrees on the Pacific to get it to run again, that's why I thought that there may be a difference between slide valves and piston valves.
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Bill Shields
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Re: walschaerts valve gear issues

Post by Bill Shields »

Inside admission and outside admission are typically 90 degrees offset..so this is expected.
Too many things going on to bother listing them.
jscarmozza
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Re: walschaerts valve gear issues

Post by jscarmozza »

Could you explain the difference to me Bill,this is the first time I'm hearing about it, thanks.
VGC
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Re: walschaerts valve gear issues

Post by VGC »

Bill Shields wrote: Sat Jan 29, 2022 3:19 pm All suggestions are assumptions that AT ONE TIME THE VG WAS CORRECT.
Not mine.
trainman154
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Re: walschaerts valve gear issues

Post by trainman154 »

ok I will get pictures of the valves in the positions that you asked for and I will post them here when I am able to.

Just a note that my eccentric is actually "keyed" in place so to speak with a set screw so I can not currently move the position of the eccentric.

Thanks
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