Does anyone know the diameter of the piston valves on an original K4 Pacifc (and also an M1a)? I am researching for a comparison of the design and performance of certain interntional locomotives, including the French Chapelon 240P, which had the same power HP output as the K4, but only a 41 sq. foot firebox, compared with the Pennsy pacific's 70.
Chapelon's work on improving the thermal efficiency of the steam locotive came after the K4 was produced, but the K4 was still a highly successful locomotive. I know that some K4s were rebuilt with 15" diameter piston valves, so possibly Chapelon's ideas on improving the ingress and exhaust of steam to and from the cylinders may have not been lost on the Pennsy,even though so few were modified.
You might want to post this in the Steam forum also they would have more info on this. IIRC from my travels 20 years ago to the Altoona RR Museum the K4 had a 13 inch Valve the M1 had either a 14 or 15 inch valve. The M1a's were built with a 16 valve again IIRC I am not the best on steam give me diesel questions and I am your man.
The only PRR K4 diagram I have which gives the valve size indicates that it was 12".
Other sources indicate that the M1-M1a-M1b 4-8-2s also had 12" valves.
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