Valve Pilot workings?

[train18393]

Exactly what is a Valve Pilot, and briefly how does it work. I understand pretty well how a steam engine works, but I am always learning. I think it monitors the speed of the engine, but what happens when the drivers slip? Does it record the speed in the cab, or just indicate the speed in the cab, and stop the locomotive if it exceeds the max speed as set by the company. I have mostly seen it on Niagras, Hudsons and various NYC engines. Of course that could be because I have the most books and vidoes of the NYC.

Is it somehow connected to the ATS equipment?

Thank You,

Paul

Dayton and Mad River (Model) Railroad

[tomikawaTT]

If my memory isn't too badly at fault, the valve pilot was a mechanism designed by a NYC engineman, which may explain why it was common on the NYC and less common elsewhere.  Its purpose was to monitor the cutoff setting of the valve gear and provide the engineer with information on how to optimize it - and thereby operate most economically.  It had little to do with speed (except that operating at speed with too little cutoff wastes steam) and nothing at all to do with ATC.

Chuck (former NYC fan)