• Johnson wheel?

  • Discussion of steam locomotives from all manufacturers and railroads
Discussion of steam locomotives from all manufacturers and railroads

Moderators: slide rules, Typewriters

  by ExCon90
In the Long Island forum is a link to a US&S explanation of cab signals; on the first page is a shot of the interior of a PRR steam locomotive showing a wheel with a handle in front of the engineer and slightly to his left. It looks as though it must be the reversing gear as found on many German locomotives and possibly others, and no sign of a Johnson bar. I had the impression that the Johnson bar was used on all American steam locomotives and that a wheel-and-screw arrangement was unknown here. Was that found on other U. S. steam locomotives?
And who was Johnson?
  by Pneudyne
My understanding is that NYC favoured the wheel-and-screw form of reverser, and used it on its 4-8-4s and also on at least some of its 4-8-2s and 4-6-4s.

Also I think it was used on some of the big 2-8-4s, including those of the Erie and some of the Van Sweringen group, including the C&O version.

Probably one could find other examples. So it had a minority but non-negligible application in American practice, right through to the end of steam locomotive production.

Allegedly it allowed finer control than the normal vertical lever associated with power reversing mechanisms. I think in Europe, it was also favoured because with its greater effective reduction gear ratio, it allowed avoidance of power reverse mechanisms on larger locomotives.

  by Marty Feldner
The reverser wheel in action in 1928 on a NYC 4-6-4...

https://www.youtube.com/watch?v=NgRyIaJePnQ" onclick="window.open(this.href);return false;
  by ExCon90
Thanks for that, especially the link. Learn something every day ...
  by Cowford
The Johnson bar is more commonly used to describe a manual reverser directly linked to the valve gear. Screw-type reversers in the U.S. were always (anyone correct me if I'm wrong) associated with power reversers, though quadrant levers were also used with power reversers.
  by Pneudyne
In the video linked to in the 3rd post, it appears as if the engineer was having some difficulties with the throttle control. It looked as if he had to jerk back on it quite hard to make sure that it was fully open. In contrast, rotation of the cutoff control wheel looked to be quite easy, not surprising given that the reversing gear was power operated.

That made me wonder whether there was a definite place for power operated (or power assisted) throttles. Such were certainly available, as indicated by the attached American Throttle Master items from Locomotive Cyclopedia 1950-52:
Locomotive Cyclopedia 1950-52 p.587.gif
Locomotive Cyclopedia 1950-52 p.591.gif
I gather though that power-operated throttles were not used very much. A.W. Bruce suggested that they were not liked by enginemen because they took away the “feel” to which they were accustomed:
Bruce p.179.gif
In that regard, perhaps a power assistance mechanism would have been more acceptable than the fully power operated type.

The Throttle Master actuating unit looks as if it were of the pneudyne type rather than being a simple air cylinder with a return spring. That is, control air pressure determined the position to which the actuating unit power piston would move using main reservoir pressure as power air. That way throttle valve opening would correlate with the engineer’s control valve handle position, and assuming adequate operating power (combination of power air pressure and piston size), the throttle position would not be affected by friction/stiction in the linkage and throttle valve assembly.

I understand that the Pennsy S2 steam-turbine prototype used pneudynes for control of both the forward and reverse turbines, from a single lever with a dog-leg pattern. 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.

It may be noted though that power-operated throttles (air, vacuum and electric) were found in European push-pull steam operations. And they would have been required for the proposed-but-never-implemented steam locomotive MU ideas.

Re the “Johnson bar”, nowhere have I seen any mention that it was named for an actual person. Perhaps it had a different origin?

  by Allen Hazen
Power THROTTLES may have been uncommon, but many large U.S. locomotives had power REVERSE. My impression is that (at least on some railroads, with some locomotives) standard practice was not to touch the THROTTLE for most of a run, but to control the locomotive purely with the reversing gear. (So, instead of the throttle being used to limit the amount of steam used, the limit was imposed by the valves at the cylinders: leaving them open for smaller or larger proportions of the cycle of piston travel.)
  by Pneudyne
And the fact that power reverse was developed quite early on and used very widely makes the non-use of power throttles somewhat paradoxical.

Power reverse was used quite widely outside of North America, including in the "British export" areas. South African Railways is reputed to have had the viewpoint that when it came to steam locomotives, the more American mechanical features that were icluded, the better was was the result. But the British builders were throught to be better on the thermodynamic aspects.

  by Pneudyne
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.