Hi everyone, so I was examining pictures of various steam locomotives when I noticed a strange characteristic of certain locomotives’ valve gear. I was looking at a picture of an L&N ‘Big Emma’ 2-8-4 in particular when I noticed that the reverse arm (located on the locomotive’s left side when looking at the front) is facing the opposite direction of usual Walschaerts setups.
Now typically the arm takes the shape of an L, but these examples were flipped. The arm in this particular setup is a backwards L, with the long side pointing to the cab. The valve gear frame is also a bracket that extends behind the expansion link, rather than in front of it (a triangle frame) or past both ends of it (a bar frame). This arrangement exists on a number of other modern steam models, including MoPac’s 2200-class 4-8-4s, Frisco’s 4-8-4s, and the B&O’s mighty EM-1s, among others.
So, what’s the reasoning behind this difference, and how does this setup work? How does the arm pull the gear into reverse? If the arm is facing backwards, then wouldn’t pulling the reach rod just cause the lifting link/mechanism to go down rather than up? I’m confused. If anyone could clear this up I’d appreciate it, thank you.
If you go to the Trains Magazine collection forums and post your question the steam and preservation forum, you will probably get at least one answer.
Very few people even look at this forum.