Pneudyne wrote:The only mention that I have seen of an air-operated throttle on a conventional American steam locomotive was in connection with one of the Union RR 0-10-2 locomotives. But that was probably a couple of decades back and I have not retained the link.
I have found the reference. It was mentioned in a thread in the “old” Railroad.net forum. That thread was “Multiple Working of Steam Loco's”, and ran from late 2002 into the first quarter of 2003. To quote therefrom
“The Union RR switchers [0-10-2] that were shipped to DM&IR in late 1940's had this air operated throttle installed.
“The Union 304/DM&IR 604 on display at Greenville, PA had this throttle until put on display. We replaced the air-brake looking handle with a conventional throttle lever and removed cylinder from steam dome.”
I looked through King, “Locomotives of the DM&IR". There was no mention of air-operated throttles in connection with the ex-Union RR 0-10-2 fleet. However, the following was said (on p.208) about the ex-DM&N S6 class 0-10-0 switchers:
“During the 1940s, “Pneudyne” air throttles were applied, affording fingertip control, a feature which enabled smoother starting of these powerful engines when handling cuts of loaded ore cars often weighing over 10,000 tons.”
Possibly the same modification was done to the Union 0-10-2s when they passed to DM&IR, and for the same reason. One may reasonably infer that the air throttle had specific utility in this case. One could also extrapolate to the notion that the air throttle might also have been of utility on road locomotives that were inclined to be slippery when starting heavy trains, perhaps because they had overly optimistic factors of adhesion.
The Pneudyne was a Westinghouse product, although whether the name was trademarked I do not know. Possibly Westinghouse offered an air throttle assembly in competition with the Throttle Master. Or perhaps the latter used a Westinghouse Pneudyne actuator as such, rather than an own-build clone.
Re the idea of operating steam locomotives at wide open throttle (WOT) as much as possible, and controlling speed by adjusting the cutoff, as I recall Wardale advocated this and furthermore suggested that the throttle levers should have no notches, other than the final WOT notch, over the upper part of their range, thus forcing engineman to use WOT unless they wanted to hold the throttle lever at some lower setting. I imagine that would have been resisted as not particularly practical, as there would likely be some situations where somewhat less-than-WOT would be desirable.