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Rhymney Railway R Class



Stephenson’s built the first three locomotives of the R class in 1907. Although based on the design of the Ms, they had quite different boilers with a slightly larger barrel and a Belpaire firebox, and cylinders with the valves between the cylinders rather than above as in the Ms. Two more Rs followed in 1909. The last batch of Rs, known semi officially as the AR class, were delivered in 1921 and will follow in another entry.

The Rs are commonly held to be the major influence on the GWR 56xx, although to be honest the family style was so strong between all the Rhymney inside frame types that making a distinction seems futile.
The most obvious difference between the Rhymney locomotives and the 56s is that the GWR design had piston valves above the cylinders, whilst the Rs had slide valves mounted between them. This is not, of course, evident in the sketches.


This sketch is based on a 1908 Stephenson's drawing of the 1909 batch. Later in their Rhymney lives there were safety valve and front suspension changes. The GWR changed safety valves again, and in several cases installed Std 2 boilers. I have a drawing in preparation for the Std 2 boiler, but I am uncertain of several details. That may have to wait until the AR article.

The earlier R conversions were, as might be expected, all of the pre war engines, yet the GWR drawings I have, although prepared before the first conversions were made, shows AR frames and I am not clear whether the converted Rs received the suspension and frame changes which would be needed to exactly match the drawings. 

Edited by JimC
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As noted above ideally I would include a drawing of the Std 2 fitted version of the R, but I haven't got any kind of good source drawings. On the one hand it shouldn't be hard to get something very close, especially, as noted, the GWR used the same arrangement drawing for both. On the other hand, because they are so similar, one can just look at the AR drawing and shorten the front a few inches. The Std fitted AR is in a comment on this entry. https://www.rmweb.co.uk/blogs/entry/25276-rhymney-railway-r-class-ar/


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