Superheaters and Throttle Linkage

[NW Mailing List]

I've read somewhere that the front end throttle was developed (at  
least partly) to solve the problem of superheater tubes burning out  
because they were empty of steam when steam dome located throttles  
were closed.  (The steam ran from the throttle valve through the  
superheater and then into the cylinders.)  The front end throttles  
were downstream from the superheaters, so the heaters were always full  
of steam.

The tube burning issue probably related to the way a particular class  
of locos was operated and the degree of superheat.  I THINK that later  
locos had higher degrees of superheat and most likely longer tubes  
more susceptible to burning out.

The multiple-valve front end throttles may have been easier to  
operate, particularly at higher pressures (although I THINK that most/ 
all dome-located throttle valves were "balanced" , so engineers didn't  
have to work against boiler pressure).

pete groom
On Aug 25, 2008, at 6:06 AM, NW Mailing List wrote:


> 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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