Re: Superheated vs Saturated

A superheated engine has the same tractive effort as a saturated engine. One of the saturated Mudhens (like 460) had the same tractive effort as a superheated one (like 463). Tractive effort is a function of steam pressure against the piston.
Superheating the steam gives it much greater expansive properties, even though the actual pressure is the same. This allows you to get more work out of same amount of steam. This greatly increases efficiency and raises the horsepower rating of the engine. So in theory, a saturated engine can start and pull the same size train as a superheated engine. The superheated engine will pull it faster and use less fuel and water to do the same work.
When Knotts put 464 back together in the 1970's, the pulled the superheater out of it for maintainance reasons. In order for a superheater to work, you have to get significant amounts of steam running through the elements within the superheater tubes, plus be working the engine hard enough to pull a draft through the tubes to heat up the steam. Knott's never worked 464 hard enough to make use of a superheater. Both 340 and 41 were always saturated steam (along with the rest of the D&RGW's 2-8-0's.