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Setting Valves with Stephensons Crossed Eccentric Rods.
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Author:  Dennis [ Thu Aug 05, 2010 7:50 am ]
Post subject:  Setting Valves with Stephensons Crossed Eccentric Rods.
Can anyone tell me whether there is any difference in setting valves on a locomotive with Stephensons Valve gear with crossed eccentric rods than one with normal eccentric rods. Crossed rods is where the bottom eccentric rod is the fore gear eccentric rod and the top rod is the back gear eccentric rod, where normally the top rod the fore gear eccentric rod and the bottom rod is the back gear eccentric rod.
Do crossed eccentric rods mean that the valve gear is set differently?
Author:  Kelly Anderson [ Thu Aug 05, 2010 8:58 am ]
Post subject:  Re: Setting Valves with Stephensons Crossed Eccentric Rods.
.
Author:  Dave [ Thu Aug 05, 2010 12:10 pm ]
Post subject:  Re: Setting Valves with Stephensons Crossed Eccentric Rods.
Are you working on a small tank engine with the eccentrics on the front axle and the valve gear working through a rocker arm towards the rear? That is the setup I've seen most with crossed rods. Your question brought up some interesting memories.

dave
Author:  Dennis [ Fri Aug 06, 2010 3:26 am ]
Post subject:  Re: Setting Valves with Stephensons Crossed Eccentric Rods.
Thank you Kelly you have described the scenario of what was happening exactly, that is diminishing lead the closer to got the valve was to mid gear.
At Full Gear the lead was 3/4"
At 75% the lead was 5/32"
At 50 and 25% cut off, no lead at all.
This amount of lead is consistent in fore and back gear and on front and back dead centres.
My problem was that in all the instructions I have on setting valves with Stephensons valve gear locomotives not one mentions the scenario with crossed eccentric rods that lead decreases the closer you get to mid gear..
Dave the loco is an 1886 Fowler 0-6-0 tank with outside eccentrics 150 PSI, 6 square feet of grate area and 11" x 18" cylinders.You can just make out the motion.
Image
Its a thirsty hungry machine.
A video can be found on YouTube http://www.youtube.com/watch?v=8NJDZlldYaE
Author:  Dave [ Fri Aug 06, 2010 10:20 am ]
Post subject:  Re: Setting Valves with Stephensons Crossed Eccentric Rods.
No smiley face.......thanks. Blue is about right, though......

Nice little girl. Probably designed for full-gear moving of a lot of weight very short distances, like the industrial tank engines I referred to above using something inside and similar, but facing the other way.

There's a very small 4-4-0 in private hands in Texas with outside eccentric Bagnall Price gear that looks something similar. Outside disk eccentrics were very uncommon on this side of the pond.

dave
Author:  Dennis [ Sat Aug 14, 2010 6:40 am ]
Post subject:  Re: Setting Valves with Stephensons Crossed Eccentric Rods.
Thank you for your replies, the information is much valued.
Another question that you might be able to answer.
This 1886 vintage locomotive has no drawings or dimensions other than those for the new boiler.
With Stephensons valve gear with crossed rods are the eccentrics set at an angle of retard or advance?
Is it possible to measure this angle whilst the eccentrics are fitted to the loco.
The reason I ask is i want to collect all relevant information and put the information into into a valve simulation program http://www.avocetconsulting.com.au/modeleng/ then play with the length of the D Valve which currently has about 1 inch of Lap.
I have about 1/16th of an inch at 100% cut off, 3/16th of an inch lead at 70% cut off and none at 50% or 25%. I want to see if by reducing the length of the D valve in small increments whether it will improve my lead any and whether I might get some lead at 50% cut off which I would then set as the running cut off.
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