Inside valve gear

And yet many Gresley designs have outside valve gear driving the inside valve, and that can be set up to work satisfactorily.

 

Gresley was prepared to accept a degree of inaccuracy with the inside cylinder valve events which Churchward and Collett were not. In the same way when Holcroft designed conjugated gear for the first Maunsell southern 3 cylinder locomotives he arranged the conjugated gear so that it bypassed the valve rod expansion, but for whatever reasons it wasn't repeated and the Southern engines ended up with 3 sets of gear. Its all about the specific compromises each each CME is prepared to accept in different areas of the design.

There's a sentence in Cook's Swindon steam "GW locomotives had extreme regularity in their exhaust beats, and we certainly could not permit of anything like two beats and a woofle which was noticeable on some rival lines." I do believe such an exhaust from a particular rival line (not the LNER) is audible to this day!

I'm not sure many (?any) of us are really in a place to say definitively which compromises were right and wrong, but we can be aware that such tradeoffs existed right through the designs. We enthusiasts have a habit of picking and choosing certain - usually externally visible - design factors as being vital and ignoring other less exciting factors, but we should at least be aware its a lot more complicated than that.

 

The 15xx was intended for Newport Docks, unfortunately it turned out to be too wide to be usable there, so they ended up
the Eastern end of the GWR main line.

( Presumably they were inspired by the WWII U S military shunters and interestingly the Southern before it brought some of these
did produce an outline design to build their own version of something like them. )

 

Re. the 15xx Class; what I read some time back about their origin was that it came from the directors, who strongly objected to panniers with great big domes hauling ECS into Paddington, and said they looked ridiculously old-fashioned. How true that is, I've no idea. Mind, when I think about the bat-brained decisions I've seen some directors make during my working life . . . who knows?

 

When the middle valve was inspected it was found that the valve had been hitting the end cover. Therefore they changed to using three sets of valve gear.

 

There is an anecdote to that effect in Cook's book. As the GWR continuied to build and design tank locomotives with steam domes my personal opinion is that its an amusing anecdote that has grown in the telling. Rather more to the point was that if a larger boiler than the P class was required on an 0-6-0 tank, they could either use the domeless Std 10, already in very successful use on the 2251 class 0-6-0 with the same size cylinders, or else design a complete new boiler.

 

In view of the GWR's preference for as many standard components (and hence standard tooling) as possible, that sounds a far more likely explanation.