Brass Question

[NW Modeling List]

Dome throttle engines have a really long path from the throttle to the cylinders, more so if they are superheated. This could be 85 feet (throttle to super heater header, then four passes through the super heater unit, then the path to the cylinders). Front-end throttles have a significantly shorter path - maybe four-five times shorter. Benefits include quicker response to throttle openings and closings and less pressure drop from the throttle to the cylinder with the front end throttle. So a sharper running engine.

With a front end throttle, Auxiliaries, such as air pumps, stoker motors, and even whistles can use superheated steam - even if the throttle is closed (as John said, the the throttle is downstream of the superheater). This is a significant efficiency improvement, and reduces chance of water condensation for those appliances since the steam is about 2-300 degrees hotter.

From a maintenance perspective, front end throttles protect superheater units from being burned when the throttle is closed since those units are filled with steam to absorb the heat. In a dome throttle locomotive, the superheater units are dry when the throttle is closed, so there is no medium to remove the heat of the fire (dome-throttle locomotives try to mitigate this by putting a damper at the end of the superheater flues to divert firebox gasses to regular flues). 

The steam delivery system is a fascinating topic!

Matt

> On Jan 9, 2025, at 10:19 AM, NW Modeling List <nw-modeling-list at nwhs.org> wrote:
> 
> Front end throttles are after the superheater. Dome throttles are before the superheater. There are several impacts of what the change does operationally and thermodynamiclly.
> 
> John Rhodes
> 
> 
> On Thu, Jan 9, 2025, 10:10 AM NW Modeling List via NW-Modeling-List <nw-modeling-list at nwhs.org <mailto:nw-modeling-list at nwhs.org>> wrote:
>> Pardon my ignorance, Mr. Jimmy, but what does that do exactly. If you don’t mind answering, I would appreciate it. I don’t know a lot about steam engines, but I’ve never heard of that.
>> Sent from my smart phone cuzz I’m just high tech like that, know what I mean?
>> WALLY 
>> 
>>> On Jan 9, 2025, at 05:41, NW Modeling List via NW-Modeling-List <nw-modeling-list at nwhs.org <mailto:nw-modeling-list at nwhs.org>> wrote:
>>> 
>>> David, your model is missing a continuation of the throttle rod between the back of the sand dome and the equalizing lever on the boiler.  
>>> 
>>> The Y5s were to my knowledge the only Ys that used this particular throttle, so your supposition about the class of your model is correct. Not all Y5s used this throttle though. Later Ys (and As/Js) used an American front end throttle - it’s spotting feature is the large access plate behind the stack (and the throttle actuating lever just below it on the right side of the smokebox). 
>>> 
>>> Matt Goodman
>>> Columbus, Ohio
>>> 
>>> Sent from my mobile
>>> 
>>> On Jan 8, 2025, at 10:38 PM, NW Modeling List <nw-modeling-list at nwhs.org <mailto:nw-modeling-list at nwhs.org>> wrote:
>>> 
>>> 
>>> It is a Bradford Front End Throttle.
>>> 
>>> Jimmy Lisle
>>> 
>>> 
>>> 
>>> Sent from my Verizon, Samsung Galaxy smartphone
>>> 
>>> 
>>> -------- Original message --------
>>> From: NW Modeling List <nw-modeling-list at nwhs.org <mailto:nw-modeling-list at nwhs.org>>
>>> Date: 1/8/25 7:20 PM (GMT-05:00)
>>> To: NW Modeling List <nw-modeling-list at nwhs.org <mailto:nw-modeling-list at nwhs.org>>
>>> Subject: Brass Question
>>> 
>>> Hi society,
>>> Does anyone know what this little thing in front of the smokestack is? This is supposedly a Y5.
>>> David Baker
>>> <1000005460.jpg>
>>> 
>>> 
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