Two Rod and Valve Gear Questions

[NW Mailing List]

Good morning, 

 

The whole debate about poppet valves rumbles on. They were claimed to be more efficient and variable to make the most of the steam expansion. The maintenance costs may have been hobbled because of the lack of familiarity with the design and operational requirements. There were some concerns over the high back pressure and these might have been overcome if the sentiment against further steam loco development had not been so strong 

 

One of the  Pennsy T1s was re-fitted with an external cam drive and I believe the project to build a new T1 is adopting this technology set. The NYC had a single Niagara fitted with poppet valves but did not seem to find favour. I believe the CB&Q also fitted one of their 4-8-4 locos with poppet valves and the UP had a design concept (FEF 4) that also featured this equipment. 

 

The Caprotti valve gear was used on a number of late build UK locos. The most notable is the Duke of Gloucester which has a three cylinder arrangement and has proved to be a very powerful locomotive since it was rescued and re-built.

 

Phil Mortimer   

 

From: NW-Mailing-List [mailto:nw-mailing-list-bounces at nwhs.org] On Behalf Of NW Mailing List via NW-Mailing-List
Sent: Wednesday, August 8, 2018 10:44 PM
To: NW Mailing List
Cc: NW Mailing List
Subject: Re: Two Rod and Valve Gear Questions

 

The boiler weight would remain the same and carried by the front and rear engines but the weight on drivers is going to change as the fuel load and water is consumed from the front & rear bunkers. Normal articulated engines have a constant weight on the drivers as the fuel & water consumed would  be taken from the tender which has no relevance to the weight on drivers or weight of the engine. The tender gets lighter but that has nothing to do with it.

 

I have no proof but I'm sure N&W steam designers as well as the major builderswere aware of the Garretts and other developments and considered them. The poppet valve mechanisms developed in Europe long before the limited experimentation in the US.

 

Roger Huber

Deer Creek Locomotive Works

 

 

On Wednesday, August 8, 2018, 8:52:48 AM CDT, NW Mailing List <nw-mailing-list at nwhs.org> wrote: 

 

 

On 8/7/2018 5:13 PM, NW Mailing List via NW-Mailing-List wrote:



They were certainly interesting to watch running. So odd seeing ll that firebox just hanging out in the breeze. Not being an expert in anything I would say the engine with thee water bunker would have to lose a lot of traction as the tank was emptied. The tender with the fuel bunker would suffer the same fate. Those could be  rather bad features. Conventional articulateds wouldn't summer that problem except the Triplex and VGN engine which were not very efficient for other reasons.

 

 

(snip)

Since the boiler weight is suspended between the two engines, would it not still have just about as much traction as a standard articulated?   Also the tender shell weight is also still on the engines rather than being drug behind. Granted full tanks and bunkers would give the best results and, since they are usually full when starting a train, I can see where that would be an advantage.    

Wonder if any American loco builders or individual roads did any research or comparisons between Garretts and our standard articulated locos ??

While not exactly pure N&W stuff, it is an interesting discussion. 

 Take care
Bill 

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