Johnsonbar vs throttle
 

Well here is something else I thought you all might find interesting about prototype steam locomotives. That is should the johnson bar or throttle be used to control speed. After some research here is what I found:

Given if we were talking about a modern locomotive such as a Southern Ps-4 the answer would be quite simple the Johnson Bar. The answer as to why is multiple, and makes the assumption that you are running an engine that is of medium to large size, has superheaters, and piston valves. If you were to ask that question in 1901 the answer would be for the most part completlely different.

My experience in live steam is mainly with wet or saturated steam engines with a d-valve, you can eqaute these engines pretty close to live steam size engines. They run pretty much the same, the more you open the throttle the more response you get. You don't normally hook these engines up much.The benefit of trying to adjust speed would have been little, the expansive forces were just not there like an engine which puts alot more superheat into the steam. Typically you would hook up the engine for two benefits, 1 to get more speed because you were getting back pressure, 2 to save steam. It was common while running to hook up normally within 100' or so of pulling out of the station, and before the running brake test and then never again.

Superheated engines however are run completely different, although there are a number of changes that make how these engines run a complete different experience. A superheated engine would be typically started by moving to full gear, then cracking the throttle to allow balancing psi. to encompass the throttle valve. After the valve reaches balance you would give it a hefty pull, at that point you would typical do one of three things, close the valve becuase you have either started to slip or are now moving with enough speed, keep the valve the same because you are moving fast enough and gaining quick as you would like, or give it more throttle. Again once moving you normally hook up some, since these engines almost all had power reverses that was not a chore that took both hands like my smaller older engines. Again typically you would be at full throttle shortly after starting, short of loosing traction, in which case you back down just as any other steam engine. As your speed increases and you want to get going faster you hook the engine up more, allowing the back pressure to be reduced and the exapnsion to be more effective. If while running you need to slow down and it was more practical then a brake application you would drop down some notches. Reducing the throttle had a lesser effect then that of a saturated engine, and because of the expansive forces would often not be noticed. The other thing is that if you shut off all the time your fireman will have a hard time trying to keep the fire light and bright. Typically you would run then full trottle or in the drifting notch, keeping just enough steam to the chest to keep lubrication and the clyinders hot. One big problem with the piston valve and superheating was that lubrication would disappear and cause carbon build up. Superheat was not a new thing when used on the railways, it was not implemented right of way because there were not suitable lubricants that could handle superheated steam in railway use.

I cannot speak for overseas, but I found that all but the largest and most powerful engines in the states did not have chest gages, but would more often in the day have a pyrometer. Keeping hot dry steam was the goal for the engineer to be running the engine in a manner that saves the most fuel and water, the chest gage was of little importance since it was typically near boiler psi anyway. The only exception would have been compound engines, or engines which run to simple engines such as the challenger.

At any rate whilst slowing down to a stop on either type of locomotive its more desirable to drop air psi on the brakes(and bailing the engine off) and make an application and drag the brakes while the engine is working instead of drifting to a stop. Typically not shutting off untill just before you want to stop. Most always while running you want the train slack pulled out, so keeping the engine under power is desirable, you can also run it all in, but its not as easy to start up again and run the risk of doing a knuckle check. Slack action is one thing that countries in euorpe don't deal with the same as they often pull their cars tight against buffers and don't have draft gears as we do in the states and other countries that use similiar set ups. The trains by 1920 were in the states large enough that procedures for running had changed to include handling the engine in a manner conducive to not break the train.

One other thing that I think most live steamers understand but I feel I should state is that no two types of engines run the same, you have to talk in terms very broad. A passenger engine would run entirely different than a freight engine of the same vintange, and a mike different then a mountain or atlantic.

In live steam its simply not very practical to control speed with the johnson bar, when running I generally run as far back as I can but if starting on a hill or with a heavy train I'll drop it into the corner... then once I get rolling start notching back. On my locomotive the fuel savings arent really that noticable, but on a locomotive such as Joe Holbrook's 4-6-2 its amazing how noticable notching back saves fuel.

Any questions please ask and I will try and elaborate. Also I welcome anyone else to chime in and give their opinions, I certianly am not an expert on these things, but as I research things like this for my Ps-4 project, I think that you all might find it interesting so I post it.
- Andrew