Valve Gear Trivia

[Dick_Morris]

I was looking at the Baldwin Steam Locomotive Standards that Little River Locomotive Company reprinted. The valve spools specified for Baker gear were somewhat different than those for Walscherts to compensate for differences (errors?) in the Baker gear motion. (I learn some important things in the bathroom.)

[Phill]

Dick,

Good question.... As I have had VERY LITTLE to do with Baker valvegear, I am not certain as to where the error lies. I do believe that the use of the bell crank adds an error to the motion of the valve gear. How they compensated for this is, at this pressent time, beyond me. None of my books have much to say about Baker valvegear. *sigh* We've lost so much knoledge....

Cheers,

Phill.

[Dick_Morris]

I looked again and it looks like I was led astray by a note which says, "Valves operated by Baker valve gear, do not travel the same distance each side of center between ports, and dimension "A" provides for this uneven travel."

I anyone wants to puzzle it out, I'm posting the bushing drawing.

[David Powell]

I am certainly no expert on valve gears( the maths of complex geometry is beyond me) but I do have a lot of experience in making models go. At present i have 2 engines to the Martin Evans Caribou design with Baker Valve gear. To get a good performance with the first one took a lot of " whittling" which included inceasing the angle which the main swinging link could move, decreasing the lead by making longer valves and resetting the return cranks and of course modifying the length of thr rods between the return cranks and the linkage. I thought that perhaps this all was needed because there were some mistakes in the manufacture of this particular model, however, the second unfinished engine I bought, which is of Immaculate workmanship obviously exactly to the drawings, shows on air almost the same characteristics of the first before modifications. I will not start modifying things until I have given it a fair trial as is but I am sure some changes will help. I spend quite a lot of time on valve setting and " whittling" on my models and feel the performance I get is ( usually) well worth the effort. Most Valve gears respond well to treatment, though sometimes one cannot get an engine to run exactly as well forwards and reverse in which cases I do not worry about reverse so much but concentrate on the most used direction and the usual condition, that is does the model spend most of its time in full gear or most notched up and get the best running where most used. Good safe steaming to all. David Powell

[Phill]

I had a quick read of my books, and, they all indicate that the error comes from the use of the bell crank, and that it's incurable in the valve gear. It is posible to correct it through the bobbin proportions for one direction of travel. A slight worsening of the problem in the other dirrection may be noticed......

I always use a valvegear analisis program to determin exactly what is happening. That way I can make adjustments to erradicate some of the errors. The best program I have, unfortunately isn't available in a windows format. Fortunately I have an old computer the I run DOS 6 on, just for a couple of programs like this one.


Cheers,

Phill.