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Re: Southern Valve Gear
Posted: Thu Nov 30, 2017 10:38 am
by NP317
Bill Shields wrote:that's cool. I have a working example of the gear that I am going to use -> but because of some minor differences between center of piston and valve seat surface, have to re-design the gear.
One thing that I have learned is that as the suspension moves up and down, so does the valve timing. I had not thought about this (previously) because the engine that I am using as my example, runs perfectly square all the time - fwd or back, any cut off.
What I found after close examination, is that the main driver suspension sits on an upper stop so that the only possible travel is DOWN in the even of something really serious happening on the track. Otherwise, the main drivers just sit there and the rest of the engine works around them, keeping the valve events really square."
One of the locomotives at Kitsap Live Steamers had Southern valve gear. During operation it experienced changing valve timing due to the suspension issues noted above. I suspect the main driver had full movement of vertical throw, exacerbating the situation.
The owner replaced the valve gear with Walshearts gear, gorgeously made, and solved the changing timing issues.
Interesting to me the different gear designs, and resulting operational variables. Humans are creative.
~RN
Re: Southern Valve Gear
Posted: Thu Nov 30, 2017 10:59 am
by BClemens
OK, the optimum bell crank angle is 15° - that can be modified at this point because the other bell crank 'arm' hasn't been placed yet. I forgot to transfer from the original drawings the center-line of the valve when this was started. So 15°...
Re: Southern Valve Gear
Posted: Thu Nov 30, 2017 11:29 am
by BClemens
NP317 wrote:Bill Shields wrote:that's cool. I have a working example of the gear that I am going to use -> but because of some minor differences between center of piston and valve seat surface, have to re-design the gear.
One thing that I have learned is that as the suspension moves up and down, so does the valve timing. I had not thought about this (previously) because the engine that I am using as my example, runs perfectly square all the time - fwd or back, any cut off.
What I found after close examination, is that the main driver suspension sits on an upper stop so that the only possible travel is DOWN in the even of something really serious happening on the track. Otherwise, the main drivers just sit there and the rest of the engine works around them, keeping the valve events really square."
One of the locomotives at Kitsap Live Steamers had Southern valve gear. During operation it experienced changing valve timing due to the suspension issues noted above. I suspect the main driver had full movement of vertical throw, exacerbating the situation.
The owner replaced the valve gear with Walshearts gear, gorgeously made, and solved the changing timing issues.
Interesting to me the different gear designs, and resulting operational variables. Humans are creative.
~RN
I tried to keep the 'right end' of the eccentric rod pivot centers as close together as possible because of this suspension/timing issue. Studying most all full sized Southern eccentric rods, they have the pivots for the radius hanger and transmission yoke very close together....couldn't do this in this instance..... The bell crank arms are the same length - hmm - probably worth working with the simulator a bit more.
BC
Re: Southern Valve Gear
Posted: Thu Nov 30, 2017 11:53 am
by Bill Shields
on my design, on a 5.7" total length eccentric rod, the hanger and radius pivots are just about 1.25" apart, which makes the linkage easy to build from a non-interference standpoint -> but makes suspension a bit more intrusive -> hence the lock it vertical up....which works VERY WELL for this particular loco - runs like a dream, tracks extremely well.
Re: Southern Valve Gear
Posted: Mon Jan 08, 2018 10:56 pm
by Bill Shields
I currently have a working animation using Fusion 360 that will allow me to manually change the cut-off then crank the drive wheel 'by hand' and observe the valve events.
it's kinda crude, but getting closer...