Inside vs outside admission vs indirect motion with Walschaert valve gear Inside Admission: The steam from the boiler enters into the piston by passing by the inside edge of the valve (like the center of the spool valve) Outside Admission: Steam enters the piston by passing by the outside edge of the valve (like a Slide/D-Valve or a spool valve where the exhaust is in the center of the valve and steam from the boiler is on the outside edges of the valve) With direct motion Walschaert valve gear for inside admission, the eccentric crank follows the crank pin and the radius rod attaches to the lead and lap lever above the connection to the valve crosshead. When the link block is in neutral, the movement of the valve is from the crosshead (through the lead and lap lever) and the valve movement is a parallel movement to the piston. The 2-8-2 and 2-4-0 have direct motion inside admission. With direct motion Walschaert valve gear for outside admission, the eccentric crank leads the crank pin and the radius rod attaches to the lead and lap lever below the connection to the valve crosshead. When the link block is in neutral, the movement of the valve is from the crosshead (through the lead and lap lever) and the valve movement is opposite from the movement of the piston. The 4-6-0 has direct motion outside admission. With indirect motion, instead of having forward being in the lower part of the link (below center) where the motion of the valve is the direct motion from the eccentric rod, forward is in the top part of the link where the movement of the of the radius rod is opposite the movement imparted by the eccentric rod. For inside admission Walschaert this means that the eccentric will lead the crank pin. Soo #1003 has indirect Walschaert valve gear with inside admission. As a side note, for Baker Valve Gear, there are changes in the valve gear between inside and outside admission so for inside admission it is a direct motion valve gear but for outside admission it is an indirect motion valve gear.
Posted on: Mon, 17 Nov 2014 01:42:27 +0000
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