Re: Spool/Piston Valves vs Slide Valves

Kevin et al -

A spool valve and a piston valve are the same thing; the steam pressure pushes equally
against the rings in all directions. With a slide valve, the pressure is in one direction -
down against the top of the sliding plate - as pressure increases, so does friction.

Superheated steam being dryer than non-superheated further increases the friction and exacerbates the problem, which is another reason why - in MOST cases - when superheaters were added to an engine slide valves were replaced with piston or spool valves. This was usually done by replacing the entire cylinder saddle, but in some cases spool valves were attached to the top of the old cylinders to replace the slide valves, as shown by the photo posted on [ngdiscussion.net].

- Russ

p.s. O-K, I admit it - the above is an over-simplification. But I don't have access to the relevant illustrations, and nowhere near the skill (nor the time) to reproduce them here.



Edited 3 time(s). Last edit at 12/20/2010 11:37AM by Russo Loco.