Driving a compound locomotive

Somewhere in my souvenirs I have a reference to the port area of both the 8" and the 9" piston valves. I am unable to find it at the moment but I recall that there was only a modest difference between them. The 20" cylinders fitted to 2002 in 1934 had 9" valves (the K1 and K2 Moguls had 20" cylinders and 10" valves and these dated from 1912/14 - 50% of the cylinder diameter) and I suspect that the need to be the equivalent of an A1 did not cause anyone to look much further than what they had. Larger valves could well be fitted to the LP cylinders there was not the same need to consider the inside cylinders as there was in the Pacifics.

Drawing number 12654 is for the inside cylinders and it would be helpful to be able to look at this. The HP cylinders were originally 12" but they were lined down to 10" for which drawings were checked over alongside those for the superheater arrangements in Nov. '30. The maximum cutoff for the HP cylinders is given as 90% in the drawing that I have access to (that for the LP is 75%) so that is where the reference to what ought or might be achieved using this figure. The travel of the HP valves was 8 9/16".

From looking at the base numbers that we do know and looking at the results achieved in France we know what it should have been able to achieve. How close it could have got to those figures in the state t was when the project was abandoned we don't know but we can perhaps find out. But no matter what the design state of the engine if it was never driven in accordance with best practice it would always be disappointing.