Re: Inside/Outside valve gear questions

Bill:

Inside and outside valve gear is basically that, inside valve gear is between the frames and was actuated by two eccentrics placed on the driven axle. This valve gear is named stephenson. It worked very well on 19th century locomotives as long as it was maintained which was a hassle because the mechanics had work on it in tight quarters, usually if they were lucky it was done at the roundhouse in a drop pit. When problems that developed on the road the hapless crew had to crawl under the locomotive to access it. As far as visibility from the outside there wasn't any save for the rocker arm and valve stem.

Outside valve gear became common after the turn of the century and it was actuated by a single eccentric crank which connected to the reverse mechanism and it made for a more interesting locomotive due to all of the exposed moving parts. There were several versions of the outside gear but the two most common was walscharets and baker. Two lesser used types were young which had no eccentric crank (driven from the opposite side) and southern which did have an eccentric crank.

The K-28's, K-36's and K-37's all had walscharets from the get go. The K-27's were originally fitted with inside stephenson but after rebuildings most of them were updated to walscharets.

My favorite is walscharets as its very easy to understand and was a little more common than baker. Baker had the advantage over walscharets as the reverse mechanism had no sliding surfaces that could wear out. Baker, though had a few more moving parts and some say it wasn't as smooth operating as walscharets. Some say if steam locomotives would have survived longer baker would have been the valve gear of choice.

You can goggle locomotive valve gears and somewhere there are posts that are animated where one can get a good understanding as to how they work.

This post should start a good discussion!

-'lil stan