Walschaerts valve gear

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Andy W
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Walschaerts valve gear

Postby Andy W » Thu Feb 25, 2016 1:04 pm

Most of the locos I've built have ben Midland and therefore I'm not at all familiar with Walschaerts valve gear. However, I'm assembling some for a Midland Motor carriage and want to check I've got it right.

Looking at the left hand side of the vehicle (cab to the left), if the crank pin is at 12 noon, then the eccentric/return crank will be at 5.00 o'clock.

If I then view the vehicle from the other side, and it has travelled so that its crank pin is also now at 12 noon, would that eccentric/return crank also face 5.00 o'clock or would that point to 7:00? In other words be a mirror of the other side?

I suspect they both would be at 5:00?

I hope that's clear??????

Any help gratefully received.
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essdee
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Re: Walschaerts valve gear

Postby essdee » Thu Feb 25, 2016 1:52 pm

Hi Andy,

Looking at the official photos;

That of the motor bogie, showing the left side (cyls to left), has the return crank such that a 12oc crankpin would give a 5pm eccentric crank offset.

The right hand side has the eccentric crank at 7pm.

I have inverted the RHS view to approximate a 12oc crank position, to save you standing on your head!

All best

Steve
Attachments
Steam Railmotor No. 2233 RHS.jpg
Steam Railmotor No. 2233 RHS.jpg (139.81 KiB) Viewed 5461 times
Steam Railmotor engine (side); DY 2258; RFB 61838 (2) - Copy.jpg

essdee
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Re: Walschaerts valve gear

Postby essdee » Thu Feb 25, 2016 1:55 pm

Ha! Was stood on my own head....

Obviously that should be LHS 7pm, RHS 5pm.

BW

Steve

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Andy W
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Re: Walschaerts valve gear

Postby Andy W » Thu Feb 25, 2016 3:59 pm

Thanks Steve, I'm confused though. Both cranks look as if they lie at 5:00? i.e. when viewed from their respective sides.
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grovenor-2685
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Re: Walschaerts valve gear

Postby grovenor-2685 » Thu Feb 25, 2016 4:39 pm

While you were walking round the vehicle and getting you mirror out someone turned the axle!
That of the motor bogie, showing the left side (cyls to left), has the return crank such that a 12oc crankpin would give a 5pm eccentric crank offset.
Should be 3oc not 5oc, the eccentric pin is 90 degrees from the crankpin but with a smaller throw.
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Keith
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essdee
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Re: Walschaerts valve gear

Postby essdee » Thu Feb 25, 2016 6:56 pm

Andy,

I know what you mean, that view is complicated by the coupling rod and connecting rod obscuring the boss and crank pin, but if you look again very carefully, bearing in mind that the crankpin is inline with a spoke, not between spokes, and 'project' the line of that spoke beyond the axle to the other side of the wheel, you will see that the eccentric crank offset is to 7oc, rather than 5oc position on the LHS. As confirmation, the GA drawing you copied to me shows the valve gear on the LHS, again with eccentric crank at 7oc position. As to degree, see below...

Keith - thanks for the note about 3, not 5 deg angular offset, I do recall reading that somewhere. However, I am puzzling a bit about your mention of 90 degrees and 3oc position; not sure where that comes in? Could you amplify please?

Anyway, the photos show what was indubitably built - once we interpret it correctly!!

Best wishes

Steve

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grovenor-2685
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Re: Walschaerts valve gear

Postby grovenor-2685 » Thu Feb 25, 2016 10:15 pm

Keith - thanks for the note about 3, not 5 deg angular offset, I do recall reading that somewhere. However, I am puzzling a bit about your mention of 90 degrees and 3oc position; not sure where that comes in? Could you amplify please?

Hey, I did not mention 3 or 5 deg angular offset! You said 5pm, since 5pm is the same as 5am I corrected it to 5 o'clock, and then gave the correct figure of 3 o'clock.
Getting away from the clock face, and assuming for now that the axis of the engine is horizontal, GW style. then if the crankpin is on the vertical centreline of the wheel, eg at the topmost position, then the eccentric pin will be on the horizontal centreline, the vertical and horizontal centrelines being at 90 degrees. Measuring from the wheel centre to the pin centre, then the crankpin distance will be larger than the eccentric pin distance.
If you unzip this file then click on the relevant app inside you will see it. There is a button to set the wheel to any desired angle, either 90 or 270 will put the crankpin at the top so you can see where the eccentric pin then is.
valgr10a.zip
(1.24 MiB) Downloaded 138 times

On the other side everything is just lagging or leading by 90 degrees but the relative positions are the same.
Regards

PS. Plenty more simulations here http://www.billp.org/Dockstader/ValveGear.html
Regards
Keith
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essdee
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Re: Walschaerts valve gear

Postby essdee » Fri Feb 26, 2016 9:12 am

Ah, thanks Keith - now I have had time to sit down and read through all, I understand where you are coming from.

Didn't even register that I had used pm!

Andy - I searched the files but cannot find a better illustration of the LHS of the motor bogie. Incidentally, I have a couple of shots of the mouldering remnants of the surviving railmotor, in trailer form, being George Dow's ex holiday carriage from Machynlleth. Having stood, tarpaulined, under cover for a period, in Feb 2014 it stood outside NRM's Shildon exhibition hall under shredded remnants of tarpaulin. No idea what plans there are for the future - assuming the bodywork survives long enough.

Best wishes

Steve

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Andy W
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Re: Walschaerts valve gear

Postby Andy W » Fri Feb 26, 2016 9:53 am

Thanks gents, I think I've got the principle now. The eccentric crank pin ends up on the horizontal line. I think I confused everyone with my 5 0'clock/7 o'clock nonsense.

And yes Steve I should read the GA more! That's what they're for!

Here's my interpretation of the eccentric cranks. Is this right?

Valve gear cranks.jpg
Valve gear cranks.jpg (581.67 KiB) Viewed 5249 times
Make Worcestershire great again.
Build a wall along the Herefordshire border and make them pay for it.

essdee
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Re: Walschaerts valve gear

Postby essdee » Fri Feb 26, 2016 12:28 pm

!! Nearly there..

Have another look at the pics and that GA, Andy.... or simpler, just swap your bottom line captions!

You see now why I consider anything more complicated than an inside cylindered 4-4-0 as Baroque? Walschaerts is just plain Rococo.

Have fun, and we will compare notes/crank settings at Wakefield ('goes off to check his own, anxiously'),

Steve

Philip Hall
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Re: Walschaerts valve gear

Postby Philip Hall » Fri Feb 26, 2016 1:44 pm

I find it interesting that the crankpin end of the return crank in the photograph is finished flush, like so many of them I've done where the crank is soldered to the crankpin. I know it's down to individual prototypes being different but quite nice that I'm not totally doing it wrong!

Philip

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Andy W
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Re: Walschaerts valve gear

Postby Andy W » Fri Feb 26, 2016 2:35 pm

Not even Rococo, more cubist with a twist of post modernism!
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grovenor-2685
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Re: Walschaerts valve gear

Postby grovenor-2685 » Sat Feb 27, 2016 3:21 pm

I knew I had an article somewhere with relevant diagrams, of course it was in the last volume I looked at.
Model Railways November 1974 by Dennis Allenden. A coule of the pertinant diagrams attached.
washaert-1.jpeg

washaert-2.jpeg


This issue also has an article on the Midland Business Carriage 2234 that was a conversion of the railmotor, a small drawing of the original railmotor is included but not good enough for details of the engine.
Regards
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Keith
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Andy W
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Re: Walschaerts valve gear

Postby Andy W » Sun Feb 28, 2016 9:19 am

Thanks Keith that's really useful. I've learnt a lot during this project ~ which is surely what it's all about. Chaps like you and Steve D are a blessing to the hobby.
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Build a wall along the Herefordshire border and make them pay for it.


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