Superheaters and Throttle Linkage

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Superheaters and Throttle LinkageGordon
    I guess that's what the house valves were for. To prevent any build up of pressure in the cylinders

Larry Evans
Kenova, WV
  ----- Original Message ----- 
  From: NW Mailing List 
  To: NW Mailing List 
  Sent: Tuesday, August 26, 2008 5:26 PM
  Subject: Re: Superheaters and Throttle Linkage


  One thing not covered in this discussion so far is the effect on the throttle linkage of boiler longitudinal expansion and contraction because of temperature changes for the situation where the throttle in the cab would be latched in the "off" position, so I'll post some comments for the experts to take pot shots at.

  Differential changes in length between the throttle rods and the boiler as the latter heats up or cools down while the throttle is latched in the "off" position in the cab could cause the throttle valve to be either pressed harder on its seat, or to be raised slightly from its seat.  In the latter case, steam could seep into the cylinders causing an unattended locomotive to "walk away."  There are many tales about instances where this occurred.  This possibility is one reason that heavy chains were placed on the rails fore and aft of one or more driving wheels on parked steam locomotives in shops and servicing areas.

  Throttle rods passing through the boiler probably were the least affected by boiler expansion and contaction inasmuch as the throttle rods should experience essentially the same temperature changes as the boiler and have essentially the same expansion and contraction.

  It seems to me that the throttle rods on the Ms and Ws that went from the cab over top of the boiler to the steam dome would have been the most affected by boiler length changes because they were exposed only to ambient temperatures.

  Front end throttle linkages on the exterior of a boiler had a compensating lever located about mid length of the boiler. This lever was pivoted at its center, so any expansion or contraction of the boiler length would simply change the angle of the lever slightly without changing the force on the throttle seat.

  Gordon Hamilton
    ----- Original Message ----- 
    From: NW Mailing List 
    To: NW Mailing List 
    Sent: Monday, August 25, 2008 9:06 AM
    Subject: Re: Superheaters and Throttle Linkage


    Bill - 

    The As, E2s, E3s, Js (including at least one of the J 4-4-2s) K 4-8-2s, selected Ms and M-1s, all M-2s, all S-1 and S-1a 0-8-0s, selected W-2s, all Ys except the Y-1s, and all Zs were equipped with superheaters.

    Suggest you consult the revised edition of Bud Jeffries' GIANT OF STEAM; Bud has the numbers of the Ms and Ws that had superheaters.  W-2 778 pictured in August Thieme's book has a superheater.

    The presence of a linkage to the front end only denotes the presence of a front-end throttle; most of those used by the N&W were American Multiples which were located in the superheater header.  Some Y-5s used a Bradford front-end throttle which was in a dome ahead of the stack.

    All the others had the throttle located in the steam dome; the K-1s used an external throttle rod going from the cab to the side of the steam dome.  The others had the throttle rod going into the boiler through a packing gland in the back ot the boiler head, and up to the dome.  Ms and Ws had the throttle rod going into the back of the steam dome above the boiler top from the linkage inside the cab, because the engineer didn't sit behind the rear of the firebox; he sat beside it and the throttle was up on the side/top of the boiler.

    Engines with superheaters did NOT usually have a front-end throttle, but engines with front-end throttles had superheaters.

    EdKing
      ----- Original Message ----- 
      From: NW Mailing List 
      To: nw-mailing-list at nwhs.org 
      Sent: Monday, August 25, 2008 1:20 AM
      Subject: Superheaters and Throttle Linkage




      I was looking at the picture of Y-3a 2077  on the August page of the NWHS 2009 Classic Calendar and noticed that it didn't have the throttle linkage on the engineer's side to the smokebox like the Y-6's and and A's.   After doing a little bit of research I discovered that locomotives with a superheater usually had a front-end throttle which I hadn't heard of previously.   The linkage on the Y-6's and A's apparently go to such a front-end throttle.  I guess this means that the Y-3's, or at least this one, were not superheated.  I think that the actual throttle valve in a non front-end throttle situation was located in one of the domes; in the case of the Y-3a, I would guess that it would be the 2nd dome back from the stack.  The dome just behind the stack appears to be a sand dome.  My questions:  how did the linkage get from the cab to the dome that had the throttle - nothing is apparent in the photo.  Also, which N&W engines were superheated?  Were the J's? Were the K2a's?  Were the K1's.?



      Thanks, 

      Bill Mason 


        



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