Posted by: Mike Clark
I know nothing about locomotives or thermodynamics and little enough about Stanleys but one difference which may be of significance is that the Stanley boiler is at a very high pressure and feeds throttled steam through a steam pipe which is much smaller relative to the cylinder volume than the steam pipe in a locomotive.
Stanley used a high pressure so as to produce a large volume of steam from a small boiler, throttling the steam and using it in the cylinders at much less than boiler pressure. David has commented on this in another place where he said that in normal running on flat roads his car needs only 150 psi and that steam chest pressure only goes up to anywhere near boiler pressure when climbing a very steep hill.
Clearly having an engine which is much too big for the boiler’s continuous output is what gives the Stanley its magnificent torque and acceleration but is it an efficient way of using steam? Does the steam waste a lot of its energy being expanded through the throttle and inlet system down to 25 percent of boiler pressure before it even gets to the piston? It would be interesting to know what percentage of boiler pressure was found in the steam chest of locomotives under average running conditions.