Herb Kelsey Wrote:
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> ... Engines with piston valves and Stephenson
> valve gear often had the piston valves inboard to
> line up with the gear and most outside mounted
> valve gears, like Walschaerts and Baker, link to
> the outboard piston valves. The aforementioned
> K-27's [454, 456, 458 & 461] had their piston
> valves actuated by Stephenson valve gear when
> they were first installed and had to be modified
> with a crossover link when Walschaerts gear was
> installed ...
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See my old drawing of a K-27 with "inboard" valves and Walschaerts valve gear on [
ngdiscussion.net].
Note the addition of a 'crossover link' or rocker arm to the above four engines, versus the direct linkage to the top of the lap-and-lead lever on the "outboard" piston valves of #463 as pictured here on 09/15/09
:
To illustrate the other interpretation of your question - inside vs outside
VALVE GEAR as opposed to inside vs outside
ADMISSION, note that #315 has inside (Stephenson) valve gear and outside admission "D" valves in her square steam chests, whereas all of the surviving D&RGW 2-8-2's have outside (Walschaerts) valve gear and inside admission piston valves in their cylindrical steam chests. The above photos illustrate the latter, while it is easy to see that #315 is quite different externally - the Stephenson valve gear is between the frames and there is no outside eccentric crank nor any other visible valve gear except the rocker arm and valve stem (which are almost completely hidden in the shadows under the running board):
In summary, here are the four usual combinations:
Inside (Stephenson) valve gear with outside admission slide valves
* (common on older engines like Eureka and #315).
Inside (Stephenson) valve gear with inside admission piston valves
** (early 1900's - first rebuilds w/ superheaters, e.g. K-27's, etc.).
Outside (Walschaerts) valve gear with outside admission slide valves (relatively rare***).
Outside (Walschaerts) valve gear with inside admission piston valves (most 'modern' steam locomotives
****).
- Russo
* Also called "D" or "hat" valves because of their shape - like a Bowler hat, with the live steam outside and the exhaust steam inside.
** Usually the result of adding superheaters to an older engine
; slide valves did not work well with the dryer, ofter higher pressure steam.
If these rebuilds kept their inside valve gear, then the new cylinder saddles would be cast with "inboard" piston valves to line up with it.
*** C&C/SP 4-6-0 #18 in Independence, Ca., is an example. IIRC, C&C 2-8-0 #1 was similar. (Would DSP&P's Mason-Bogies qualify??)
**** Baker valve gear was also fairly common
; Young, Southern and other outside valve gears much less so.
Edited 4 time(s). Last edit at 12/17/2009 04:49PM by Russo Loco.