Does anyone recognise this demonstration model ?

[Michael GilliganParticipant @michaelgilligan61133]

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It does look a little sad compared with the new-fangled animations … but I think it deserves its place in history.

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Did your classroom have one ?

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

[Tim StevensParticipant @timstevens64731]

I have seen similar showpieces on the wall in the railway museum in Nuremberg*. But they are rarely any use to the children, who twiddle the handle, nothing goes bang, so they move on.

Just in case you wish to visit with SWMBO, take your wallet as next door is a shop full of dirndle skirts.

Cheers, Tim

[SillyOldDufferModerator @sillyoldduffer]

Posted by Tim Stevens on 24/11/2022 17:26:33:

…

Just in case you wish to visit with SWMBO, take your wallet as next door is a shop full of dirndle skirts.

Cheers, Tim

Must be a typo? Tim surely meant to say be sure to leave your wallet at home. Taking SWMBO shopping without a good excuse for not spending money prioritised on important male pursuits is fraught with danger, I'm divorced!

Dave

[peak4Participant @peak4]

I did a simple repair on one for South Yorkshire Transport Museum, but it looks like I didn't take any photos at the time unfortunately; worth popping in if you're in the Rotherham area at weekends.
https://sytm.co.uk/

Bill

[BazyleParticipant @bazyle]

Potentially useful for giving a talk on steam engines or at an exhibition where someone is on hand to explain it. I still remember a club presentation from about 20 years ago that used such a model, though it may have been Stephenson's.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks folks … I just thought someone might recognise it from a ‘Lab Technicians Handbook’ or some-such.

It amused me enough to pay £2 for it at the Car Boot Sale

’though I am sure there have been much better buys shown here.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Might be a left over from a Mutual Improvement Class on BR or one of the preceding Railway Companies.

A very useful aid to understanding the operation of the valve gear.

(I can grasp Stephenson';s and Hackworth, but some of the others defeat me. Can never see the difference between Baker, or Heusinger and Walschaerts )

Howard

[Dave WoottonParticipant @davewootton]

I don't recognise that one, but someone might be able to answer a question that has puzzled me for years. When I was about fifteen I volunteered on the Bluebell railway, this would be about 1972. Someone turned up one morning in a transit van and donated a very large valve gear model, it must have been at least ten feet long and hung out of the open doors at the back of the van. From memory it must have been Stevensons gear, beautifully made from contrasting hardwoods, with brass and steel fittings and everything adjustable and calibrated, I thought it wonderful but others were less impressed, one suggestion was to break it up to light the fires with. I remember it leaning against a wall in one of the sheds and then it disappeared, no one seemed to know or care where. Then with the discovery of motorbikes and girls the Bluebell was largely forgotten, I did ask on several visits but the fate remained a mystery. Does anyone remember it or know what happened to it? I always thought it might have originated from Brighton works, but the late Bert Perryman, an expert on all things Brighton said it did not, although he remembered seeing it in the shed but did not know of it's fate. The assumption was that as it was so large and couldn't fit in the museum it was disposed of somehow. Would be really interested to find if it survived.

Dave

Edited By Dave Wootton on 25/11/2022 08:52:41

[SillyOldDufferModerator @sillyoldduffer]

Posted by Howard Lewis on 25/11/2022 08:19:51:

Might be a left over from a Mutual Improvement Class on BR or one of the preceding Railway Companies.

A very useful aid to understanding the operation of the valve gear.

(I can grasp Stephenson';s and Hackworth, but some of the others defeat me. Can never see the difference between Baker, or Heusinger and Walschaerts )

Howard

Or any of a multitude of Technical Schools, Technical Colleges, and Apprentice Training Schemes. Before dieselisation, steam locomotives were a major source of employment making it useful for many people to understand at least roughly how they worked.

Wot I know about valve gear comes from helping Duncan Webster refine and port his valve simulation software. (Duncan did the clever maths etc, my part was refining the software, helping with the GUI, and porting the beast to various platforms. )

The goal of a valve linkage is for movement of the piston to result in perfect timing of the valves, whilst allowing cut-off and lead to be adjusted by the driver, in both forward and reverse. Duncan's simulator makes it possible to compare the various valve mechanisms. The simulator identifies how good or bad the valve events are. Valve performance isn't obvious from just eyeballing the motion, it's necessary to analyse how and when the various levers interact throughout each cycle. It can be done by measuring the real thing, or – more conveniently – by having a computer do the maths. Lots of maths!

Various motions have been designed in the past to achieve perfection, but it turns out there are a bunch of trade-offs between efficiency, reliability, complexity, and ease of maintenance. For example:

• Stephenson produces near perfect results and is reliable, but the gear is slung between the frames under the engine. Great until it goes wrong, when it becomes horribly expensive to maintain. Faults take the engine off the road for ages and the lost revenue costs the company a fortune.
• Walschaerts events are nearly as good as Stephenson, but the motion is more complicated and liable to go wrong. However, it has the huge advantage of being hung on the outside of the loco, making it much easier and faster to fix. Walschaerts' became by far the most popular system for mainline rail because it achieves good fuel economy without spending too much time being repaired.
• Other systems produce inferior valve events and waste fuel, but compensate by being simple, robust, and easy to fix. They tend to appear on working engines where fuel economy isn't the top priority. Baker gear, which is easier to maintain than Walschaerts because it has fewer pin joints, was popular in the US until the cost of coal started to hurt! Then new engines were built with Walschaerts gear.

In the end steam locomotives couldn't compete with diesel, and the need to understand them dropped out of mainstream education. As a result lucky Michael picks up a nice model at a car boot for £2! I've never seen anything like that.

Dave

[duncan webster 1Participant @duncanwebster1]

I think by now we all know that SOD isn't very good at sums, but even he should be able to count the pins! Baker has a lot more than walschearts, what it doesn't have is the curved slotted link. It gives fairly poor valve events as well.

[Martin Johnson 1Participant @martinjohnson1]

There have been quite a few occasions at steam rallies when such a model would have been handy for explaining "How does it work?" One day I'll make one……….

Martin

[SillyOldDufferModerator @sillyoldduffer]

Posted by duncan webster on 25/11/2022 11:42:50:

I think by now we all know that SOD isn't very good at sums, but even he should be able to count the pins! Baker has a lot more than walschearts, what it doesn't have is the curved slotted link. It gives fairly poor valve events as well.

I blame my mentor for this latest cock-up! Though come to think of it my memory is worse than my arithmetic!

[John OlsenParticipant @johnolsen79199]

An advantage of the Baker gear is that it can be constructed such that you undo a few bolts and take the unit off the loco, replacing it with a refurbished one from stock. This keeps the down time to a minimum.

Heusinger and Walschaerts are the same thing, apart from the name of the individual claiming credit for the design. Baker is in essence the same thing except for replacing the curved link with a set of levers.

I seriously doubt if there is any efficiency disadvantage to any of the radial gears given competent design. Not that any design is ideal, the valve tends to to be moving slowly when we would like it to be moving fast. But the biggest problem is the inability to generate and use steam at a high enough temperature on a moving platform. Plus the difficulty of providing a condenser.

John

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