Valve Gears - please explain to a Numpty

Brilliant! Thank you.

 

Thank you everyone

Now to think of some more questions!

 

There's a Don Ashton analysis of the (4)4767 Valve gear here. http://www.donashton.co.uk/html/44767.html Mr Ashton seems of the opinion that in the end it wasn't a direct copy of the Swindon layout.

 

If you follow links on Don Ashton's website there are computer simulations of Walschaerts' and Stevenson's valve gear available. It is quite informative to watch the animations. Although Don is mainly concerned with the design of valve gear for models he, and others, have put a lot of effort into studying valve gears. I used the simulation programme created by Dr Allan Wallace and entered the dimensions for the Southern moguls. This gave an analysis of the valve events which matched that on the valve gear drawing so I am convinced it is an accurate model. I am also extremely impressed by the quality of the original design, especially as they probably worked out the valve events using a wooden model.

 

Mr Ashton's suggestion that the basis for 4767's construction is unknown is not consistent with Eric Langridge's story as related above, and since Mr Langridge was a senior draughtsman at Derby DO at the time, there is no reason to doubt his words.

I certainly would not though challenge Mr Ashton's analysis of the gear as applied to the loco.

 

I think he actually said that little appears to be known. It would seem the Langridge comment was unknown to him when he wrote that.

A lesson, perhaps, of the Thompson thread is that there is valuable information scattered about in all sorts of obscure and unlikely sources, and perhaps only if you gather a large body of reasonably well read people do you have a chance to capture them all. You then have the problem of disentangling entrenched opinions and misconceptions, original or modern, from the truth of the available information, but that's a better problem than not having the information at all.

 

A couple of Swindon Engineering Society lectures on the subject, given by the chap responsible for implementing the gear used on the 'Stars':—

No. 70 - Valve Motion Developments, W. H. Pearce - 03/04/1906

No. 73 - Stephenson versus Walschaert Valve Gears, W. H. Pearce - 18/12/1906