Valve Gear Varieties

Just as long as the coupling rods are still a good fit. Tom Rolt wrote a good description of it's deficiency when everything had worn loose.
Pat

 

One must never forget Chapelon super-power!

There is also the vintage "Bellerophon" 0-6-0T, which has outside Gooch valve-gear driven from the third axle.

Germany like Britain used a number of different solutions for driving the inside valve-gear of a 3-cylinder engine. The Prussian G12 2-10-0 (DRG Class 58.10), of which over 1400 were built 1917-24, used Henschel conjugated valve gear. The Reichsbahn standard classes, as you say, had forms of inside valve gear for the middle cylinder. The Bundesbahn Class 10 4-6-2 of 1957 used an outside crank on the rear coupled axle, similar in principle to the Czechoslovakian arrangement.

https://en.wikipedia.org/wiki/DB_Class_10

http://www.railfaneurope.net/pix/de/steam/10/10_001e.jpg

 

Well, no-one claimed it was an arrangement with lots of finesse!

Baxter has two notches each way in its reverser, which correspond I believe to about 75% and 35% cut off, or thereabouts. But I suspect that was more than enough variation for a life in Betchworth Quarry!

Tom

 

Whilst agreeing that Fletchers patent led to a valve gear that was compact, the real advantage of it and reaso was that it allowed the rear wheels of an 0-4-0 to be situated behind the firebox, something that was virtually impossible with Stephensons. This led to a more stable design of loco with, effectively, a wheel at each corner. More conventional 0-4-0's inevitably have a short wheelbase with a relatively long rear overhang which leads to an inevitably rougher ride. Anyone who has had the privilege of riding on Dolgoch will not doubt the suggestion that the loco provides a smooth, steady ride with no tail wag although the volute springs on the rear does give rise to a bit of a vertical motion.

 

Understood.
I was looking at a picture of 'Bodmin' recently (no, not the Bulleid one), which looks to me like a standard-gauge version of 'Talyllyn' as first built, which shows the firebox hanging out behind the trailing axle. I can understand why the good Captain commented on 'Talyllyn's' riding.
Pat

 

Was thinking we had discussed it before:

https://www.national-preservation.com/threads/paint-froth-question.1043098/page-4#post-1986126 et seq

BTW, why is that threads that start specifically to discuss paint froth invariably degenerate into serious locomotive discussion ...

Tom

 

You've a better memory than me, Tom, and reading those posts it seems that Dolgoch may have been unique so not a case of a wheel at each corner for most of the patent locos.

 

I'll bring it back round then...

What's the best colour for valve gear to be painted in?

 

Holcroft also reports on the Class Z 3-cylinder 0-8-0 tank where there was not room for conjugated motion to drive the middle valve, and they arranged a modified version of Walschaerts where the combination lever was driven from a second eccentric rather than from the crosshead; I think the 3-cylinder Maunsell moguls were also like this when the conjugated gear was removed. This is a probably a more straightforward way of driving the middle valve when it is beside the cylinder than conventional Walschaerts.

Another post mentions the German standard 3-cylinder pacifics. The same arrangement was introduced by Robinson on the Great Central when he rebuilt Atlantic 1090 with three simple cylinders, i.e. the inside cylinder drove the front axle but the inside gear worked off the second axle. The advantage would seem to be that the expansion link for the inside gear is in the same transverse position as for the outside gears. I think this was the first locomotive in the country with three sets of Walschaerts motion.

 

I find this fascinating, after 200 years qualified engineers and learned enthusiasts are still discussing the merits and improvements to be made to various types of gear.

Thought Experiment.

There is no chance of this happening but has anybody any constructive thoughts about this.

The older ones among us remember cars with the tiresome "choke" to often be used to get smooth starting and running. Cars nowadays have automatic chokes and cruise control, which work perfectly well.

Could a computer be used to get perfect valve events, with use of the following parameters. Current speed, required speed, forward or reverse, gradient, load, etc. Also is there any chance that the "O" rings produced today could be used as piston/valve rings, I am fully aware that "O" rings have failed on some space vehicles, but by and large they seem to work perfectly well,
Lastly could ceramics have their uses in the cylinders and valves.

I am quite prepared and happy to be shot down in flames for this herecy.

 

You could certainly get a computer programme to signal the opening and closure of the valves, but then you have to come up with the mechanical means to do the actual opening and closing quickly and accurately enough. The car's choke was easy; we had automatic chokes long before computers.

 

Two stroke motorcycle technology ought to do the trick, at least for a few weeks until the hostile nature of the steam engine environment catches up. The rotary disc valve might have potential.