Re: Slide valves versus piston valves

GeorgeGaskill Wrote:
-------------------------------------------------------
> Slide valves use the boiler steam pressure to
> force the valve against the valve seat, which is
> a sliding joint. This worked well enough when
> boiler pressure was not real high but as boiler
> pressures increased, it required more force to
> actuate the valves and valve and valve seat wear
> increased

. . . as did strain and wear on the valve gear. . . .

> Piston valves contain the boiler pressure within
> the spool (the valve body) and the pressure does
> not force the valve against the valve seat so they
> are easier to move and do not wear as fast.


Right, George -

When several of the K-27s were converted to piston valves, new cylinder saddles were cast.  Four of the engines retained their inside-the-frame Stephenson valve gear for a while, and the new saddles had the piston valves inboard of the cylinders to line up with the Stephenson linkage (like #461 - see [ngdiscussion.net]).  The others that were converted to piston valves also got new Wahlshearts valve gear at the same time, so the new saddles were cast with the piston valves outboard of the cylinders, like #463.

To eliminate the cost of casting new cylinder saddles, a modification "kit" was also available for a time, which consisted of piston valves that could be attached to the top of the old cylinders in place of the slide valves.  IIRC, Georgetown locomotive #111 is an example of an engine that was rebuilt in this way.  See the photos posted by F&W14 at [ngdiscussion.net] and by Shane Schabow at [ngdiscussion.net] - especially the fourth one.  It looks to me like #111 also got a front-end throttle at the same time she got her piston valves.

- Roosso



Edited 1 time(s). Last edit at 02/13/2017 01:45PM by Russo Loco.