The sound of a steam locomotive

The LMS 2P's originally had them , i believe. I seem to recall David L. Smith reporting that the GSWR men were upset at their removal in the Stanier era.

 

To the drivers, they were a wonderful invention as they gave a very free running engine with steam off. To the engineers, they were a maintenance requirement, but even more so was the problem that, should a by-pass valve stick open, the engine was a total failure as live steam would be admitted to both ends of the cylinder.

 

In 1996 I scrounged a lift on GMAM 4122 from the station/junction to Voorbaai shed which was only a short distance ,but I noticed that the driver had what looked two pull out regulator handles ,although he only spoke mostly Africana he muttered something like bypass valve. Presumably this was pulled out on the long steep downhill grades . Photo attached showing clearly the by pass valves ,also one of the Red Devil.