Re: NNG: Scenes at Steamtown

Officially that form of Walscheart Valve gear is called "Indirect Motion". It is "indirect" because in motion the eccentric rod from the eccentric crank to reversing link is moving in the opposite direction of the valve stem. You see this set up on lots of locomotives with Walscheart Valve gear and slide valves, like #26. In this set up, the radius rod is in the upper portion of the link in forward motion. You will also see it on switch engines.

The normal way is to have the radius rod in the lower portion of the link when in forward motion. This is preferred on road engines. If the Johnson Bar linkage should fail at speed, the radius rod will drop to the bottom of the link. With Direct motion gear, it simply falls to full stroke. With Indirect motion, the engine will drop into reverse! Switch engines were constantly going forward and backwards, so it made little difference.