Why did GWR steam locomotives have comparitively simple external valve gear?

[SquireBev]

Something I've always wondered, but which really struck me at Kidderminster this morning when I was able to compare a GWR Hall Class with an LMS Ivatt Mogul, is why GWR engines have very simple valve gear compared with LMS or LNER designs. Even the largest GWR designs appear to only have the main connecting rod on show, while even fairly modest LMS and LNER designs have a lot more going on.

Are the GWR machines actually mechanically simpler engines, or is it simply that the rest of the workings are hidden between the frames?

 

[AM9]

The standard practice on 2-cylinder GWR loco designs* from GJ Churchward onwards, was to have external cylinders with inside valve gear. When the larger express classes were built they were fitted with 4 cylinders but the externalcoupling/connecting rod only appearance was maintained by deriving the valve motion on the outer cylinders from the inside mechanisms.
* 0-6-0 tank classes had inside cylinders only so only coupling rods were visible.

 

[SquireBev]

Aha, I see. Thank you.

So was it a primarily aesthetic decision? Presumably it would have made maintenance more difficult.

 

[AM9]

Aha, I see. Thank you.

So was it a primarily aesthetic decision? Presumably it would have made maintenance more difficult.

The GWR was a very image-concsious railway so the near uniform appearance of locos might have been part of the marketing, especially if it enabled the size of each faster generation to be emphasised. Churchward was always held to be the father of the (then) modern GWR, so maybe his successors, Collet and Hawksworth paid dues to that epithet.

 

[edwin_m]

Was it also related to standardization? It's well known that many parts were shared between loco classes, to the extent that there have been preservation projects to re-create "lost" classes from bits of others where there are many preserved examples. I wonder if always going for inside valve gear was part of this, or of the related policy of finding something that works and sticking to it, which basically meant GWR locomotive technology didn't really advance much after the 1920s because it didn't need to. Stanier (having come from the GWR) was also a fan of standardization but he probably had more scope to start with the clean sheet with the LMS designs, including valve gear that was more easily maintained.

 

[Taunton]

There were a number of types of valve gear, and for each of them the decision whether to put them inside or outside the frames. The "Other Railways" gradually moved to outside, the GWR did not. The GW held to a very standardised set of mechanical parts, used in various combinations, so once Churchward seemed to have reached the optimum they just carried on.

Most of the developments after 1900, like Caprotti gear, claimed to offer advantages, but in practice did not live up to this.

 

[geoffk]

Stephenson valve gear, as used on GWR two-cylinder locos, was normally placed inside the frames, the exception being the now preserved LMS "Black Five" 44767, named George Stephenson (although the gear was actually named after his son Robert!)