Stephenson valve gear
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Machining
See Turning Eccentrics in Three-Jaw Chuck
Setting
- When the reversing lever (Johnson Bar) is in mid gear position there WILL be movement of the valve spindle however it will be at a minimum.
- With the covers off the valve/steam chest then with the lever/bar centred (mid gear) the valve should just open the ports and it should be symmetrical at top and bottom dead centre respectively.
- Better to set the eccentrics at full gear so that the valve only just cracks the ports at TDC/BDC and adjust the spindle length or slide position so it is symmetrical. just as you would a non reversing engine. This adjustment can be done without taking the cover off if the boiler has some low pressure air it and tubes connected to the drain cocks are led into a jar of water. Bubbles from the tube indicates the port is just opening.
See also:
- Setting Stephenson Valves
- Allen Models of Michigan catalog contains a write-up on how to set valves for an Stephenson Valve Gear.
- "Setting Stephenson Eccentrics", Maurie White, Modeltec, December 1996. Reprinted from Big Wheel News, July 1995, journal of the Steam Locomotive Society of Victoria
- "Stephenson valve setting", Chaski.org
Finding top dead center and setting values for Stephenson gear on Allen Mogul: