Talk:Slide valve

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D slide valves[edit]

First of all we need an article on slide valves in general. This wasn't / isn't it! Maybe we then choose to merge this article into one section within that article, but we need general slidevalve coverage first.

D slide valves are almost always misunderstood. The "classic" slide valves aren't Murdoch's D slide valve. That's something distinct and separate, worthy of its own coverage. Pretty rare too.

Those who haunt the Commons might have noticed that I've recently organised some cats and uploaded some scanned images. You might find these useful. Haven't yet found a free image of a Murdoch valve though. I've no time to contribute anything these days. Andy Dingley (talk) 15:49, 11 June 2009 (UTC)

I am not sure you have got this right, Andy. Firstly, D-slide valve seems to be what Americans call an ordinary slide valve. See, for example: Yoder, J. H.; Wharen, G. B. (1993) [1917]. Locomotive Valves and Valve Gears. Leamington Spa: TEE Publishing. ISBN 1 85761 026 1.  Secondly, as I understand it, the slide valve as applied to a steam engine, in whatever form, is attributed to Murdoch, but we would need a reference for that, one way or another, and to know how it evolved. Confusingly, This picture shows something that looks to me very much like an inside admission piston valve, while the curious wording of the extract from the patent (which admittedly I have not seen any more of) seems to describe an outside admission piston valve. Globbet (talk) 20:24, 11 June 2009 (UTC)
The common "short" slide valve is Murray's invention. Murdoch's is the "long" or D-shaped slide valve. Both date from around 1799 and it's unclear which came first. The crucial difference is that Murray's seals along one large flat surface the length of the valve (i.e. along the sides too). Murdoch's seals around the back of the valve instead, through a D-shaped seal at each end. Murray's needs the ability to plane a large flat surface on the cylinder (see Rolt for the costs involved in doing this). Murdoch's needs two smaller seals, but they're also an awkward shape and can't easily be tightened down with a stuffing box.
What Americans get up to is their problem. The name "D slide valve" certainly gets mis-applied everywhere, but it's still wrong if it's a slide valve with a single flat sealing surface. Andy Dingley (talk) 01:05, 12 June 2009 (UTC)
I found the on-line scan of Dalby's Valves and Valve Gear Mechanisms[1](I now want a 1906 original). This says that the Murray patent was 1802. I now have a reasonable grasp of Murdoch's arrangement. I had not understood that it was D-shaped in cross-section. The drawing of his model carriage now makes more sense. Just need to explain it more clearly here, and probably to be prepared to defend the nomenclature. Globbet (talk) 21:47, 12 June 2009 (UTC)
Problem with the patent dates is that both valves are known to have been in use for some years beforehand. The steam carriage is also thought to have used a simplified version of Murdoch's "tubular" slide valve, rather than the developed (still tubular) D slide valve. Jamieson's "Elementary Manual" of 1898 has a very clear drawing of the long D, and this is reproduced in Hills' "Power From Steam" (which is worth buying, if you don't already have it). Andy Dingley (talk) 22:56, 12 June 2009 (UTC)
Glad you liked the Commons scans. Must sit down and do the descriptions yet...

The "Slide Valve" link at the bottom would appear to be returning a 404 error and forward on to a default page. — Preceding unsigned comment added by MDodson (talkcontribs) 04:29, 22 February 2014 (UTC)