Why are there differences in steam locomotive throttles? IE why are some mounted on the roof and have a vertical appearance vs those mounted on the rear of the firebox that have a more horizontal appearance?
I've been searching the internet and can't really come up with an answer.
Thanks
Modeling the N&W freelanced at the height of their steam era in HO.
Daniel G.
Cheers, the Bear.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
The horizontal throttles are connected to the throttle valve by a rod that goes inside the boiler to the steam dome where the valve is located. The vertical levers are connected to a "front-end throttle" valve that is located at the forward end of the boiler by external linkage.
More here:
http://everything2.com/title/front-end+throttle
Dave
Just be glad you don't have to press "2" for English.
http://www.youtube.com/watch?v=zQ_ALEdDUB8
http://www.youtube.com/watch?v=6hqFS1GZL4s
http://s73.photobucket.com/user/steemtrayn/media/MovingcoalontheDCM.mp4.html?sort=3&o=27
Agree with steemtrayn. Not sure whether there were exceptions.
Tom
Yes, there were. N&W K1 locos had a verticle throttle handle that connected to the throttle valve in the steam dome.
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That's why I hedged a bit when I answered.
Actually, the K1 in the photo has a throttle rod that runs outside the boiler, in common with front end throttles. I think a (near) horizontal throttle handle generally connected to a throttle rod that entered the backhead and ran inside the boiler. But I'm on shaky ground here & will defer to anybody who can give more reliable info.
Nice engine photo, by the way.
If you will look close enough, the throttle rod exits the front of the cab and goes directly to the steam dome, not the front of the engine
Here is the inside cab view. Note the throttle in the upper right hand corner.
Thanks guys. This helps a lot.
Would it be safe to assume that the locomotives that have the throttles that are in the steam dome (vs the smoke box) are non-superheated?
dale8chevyss Would it be safe to assume that the locomotives that have the throttles that are in the steam dome (vs the smoke box) are non-superheated? Thanks
I would suggest that whether the throttle/regulator was in the vertical or horizontal plane was up to the individual locomotive builder’s design, depending on the location of the steam dome, the routing and complexity of the throttle linkage, and the mechanical advantage required to manually move the valve in the steam dome.
Be careful -- you're getting 'salty' with where the throttle valve is before you should.
Modern American locomotives don't have the throttle in the steam dome; they have what is called a 'front-end throttle', which is a cam-operated arrangement of poppet valves at the other end of the dry pipe from the dome. This is most easily actuated by linkage external to the boiler shell (although it could be run under the lagging/cleading on the outside of the boiler shell).
As a peripheral note: many larger locomotives have an intermediate lever in the throttle linkage that reverses the direction of actuation for half the linkage run. This is to neutralize the effect of differential expansion between the boiler structure (to which the cab attaches for support) and the linkage itself.
There are some locomotives that have both a dome throttle and a front-end throttle (one of them I believe is the Russian P36 class 4-8-4). I do not know how this arrangement is controlled (other than that it would be unwise to work both throttles with a common linkage) but would certainly like to find out.
Whereas there are power assisted reversing levers, or Johnson Bars, I have been unable to ascertain if any throttles were.
There were air-assisted throttles; the ThrottleMaster advertised in '40s editions of railroad trade magazines was an example. The infamous PRR T1 used a Franklin Precision air throttle, for which drawings still exist.
WizlishModern American locomotives don't have the throttle in the steam dome; they have what is called a 'front-end throttle',
Thankyou for correcting the error of my ways. Just proves that a little knowledge can be dangerous.
Another thing to note is that if an engine has a front end throttle it is therefore super heated. The reason to have a front end throttle is the steam still comes from the steam dome and is fed through the super heaters then the valve is after. With the super heated steam preheated it gives the locomotive a faster start with more energetic dryer steam. And for the sake of explaining for those that may not know, super heating steam is useful because it basically ups the pressuse of the steam making it more energetic with out putting more strain on the boiler itself. Free higher energy raises efficiency, or at least more power for no extra fuel cost.
Flickr: https://www.flickr.com/photos/60361449@N02/
Anthracite Modeler - YouTube
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One of the things we historians of the steam locomotive have to consider is the fact that we have the advantage of looking back over some one hundred-fifty years of locomotive development.
That word development is crucial in our discussions of the steam locomotive because at any given point in time there was a broad range of locomotive designs from different builders in use and the ages of the locomotives varied greatly since some fifty year old, hand fired, non-superheated engines could be working right along side the latest "superpower" from Lima or Baldwin.
The variety of locomotives depended largely on what the needs of the particular railroad were and the preferences of the Superintendant of Motive Power and Chief Mechanical Officer were. If it weren't for the likes of Paul W. Keefer or J. T. Wallace we may never have seen the New York Central Hudson or the Pennsy K4.
In just the sheer numbers of locomotives (the Pennsy had 7,556 on the roster in 1924; 4,848 in '46!) there is going to be quite a bit of room for variation.
Here's a sketch of the front-end throttle linkage that Wizlish refered to:
throttle_link by Edmund, on Flickr
The railroads learned of the advantages of superheated steam in the early 1900's. There were applications in Germany in 1898 and England in 1906. Tractive effort and economy were two major factors in the adoption of the superheater but increased maintenance costs had to be considered, too. One of the factors for the need to adopt a front end throttle was the fact that as the boiler diameter increased there was less headroom for a steam dome throttle.
throttle_a by Edmund, on Flickr
Not all the front end throttles were of the poppet variety. Here is a view of a Chambers front end throttle which is very similar in design to the steam dome type but designed to bolt directly to the superheater header.
Well, I'm using up my allotted bandwidth here so I'll close. These discussions are interesting and I hope that my 2¢ here will add to the good information already provided.
Thanks, Ed
Just to toss another shotgun shell on the fire, modern Japanese locomotives had dome throttles with outside linkages. They also had superheaters. I don't know what arrangements were used to keep the superheater loops from overheating.
The Russian Decapod also had a dome throttle with outside linkage - but no compensating link. I wonder what was done to prevent throttle creep.
Chuck (Modeling Central Japan in September, 1964)
tomikawaTT Just to toss another shotgun shell on the fire, modern Japanese locomotives had dome throttles with outside linkages. They also had superheaters. I don't know what arrangements were used to keep the superheater loops from overheating.
Interesting. And yet there was lotsa superheating before the front end throttles were adopted. One possibility is that the potentially overheated superheater tubes were surrounded by tubes that were cooled by boiler water. And that the heat radiated by the superheater tubes (sucked up from the flue gases) was absorbed by same. Don't laugh--it could/does happen.
The Russian Decapod also had a dome throttle with outside linkage - but no compensating link. I wonder what was done to prevent throttle creep. Chuck (Modeling Central Japan in September, 1964)
Nothing, apparently. It does argue for making sure the reverse gear is in the zero position. During operation, of course, our highly trained operator adjusts things accordingly. As, of course, we operators still do. Accordingly.
Ed
7j43kAnd yet there was lotsa superheating before the front end throttles were adopted. One possibility is that the potentially overheated superheater tubes were surrounded by tubes that were cooled by boiler water
Yes, the superheater flues were surrounded by boiler water but that didn't help cool the superheater tubes within those flues. There were front end dampers of various designs that would bypass the hot gases when the engine was drifting, throttle shut. Sometimes you could see a counterweighted lever on the smokebox near the front flue sheet.
The engine I'm familiar with, a 1918 USRA ALCo Light Mikado had a Superheater Company Type A arrangement with an internal damper and a double-lapped dome throttle with internal linkage.
Many different designs were out there so it is tough to generalize on one design. You have to look at each particular locomotive and with each locomotive, when—since over the lifespan of some engines many appliances were changed or removed alltogether.
Hope this helps, Ed
Here's a neat article on superheaters (and a bit on throttles):
http://en.wikipedia.org/wiki/Superheater
It mentions, but does not show, the damper.
Voilá! Here's the drawing that should have appeared in that article. For some reason they fogged-out all the juicy details.
Railroad_S_Damper by Edmund, on Flickr
I scanned it at 600dpi for clarity. You can see m the damper and n the actuating cylinder. Note that it operates automatically with steam pressure on the steam chest supply pipe. Very clever, indeed.
Nice view of the steam dome throttle, too. The engine I worked on had a slightly more elaborate bell-crank and linkage but the end result was the same.
Hope this clears things up, Ed
It does!
Especially if one notes that the flue gases come out of the flues, go down and through (or not) the damper, pass under that horizontal piece of sheet metal, proceed UP to hit the cinder screen and then proceed "backwards" before being ejected out the stack.
Yup, it is darn clever.
(Other) Ed
It was forty years ago but I've spent a few2 hours shoveling (more like scooping up with a coffee can) cinders out from around all those baffles and screens. With bad coal there's a pretty good chance of getting things clogged up in there.
The removable plates at k would allow you to rod out the plugged superheater flues with a 3/8 or 1/2" length of black pipe and blast 100 pounds of air into it. Talk about getting a soot bath!
It was forty years ago, too, that I could squeeze my way past that throttle to get inside the boiler for dry-pipe inspection and staybolt work.
Glad to pass on the information, Ed
(also) Ed
FYI.This Locomotive, No 278, has an operating Smoke Box Damper.Watch behind right steam pipe after time 3:45.https://www.youtube.com/watch?v=pzAqg94Qfuc
and here esp after time 4:40
https://www.youtube.com/watch?v=bnQF5eo_ojM
Thank You.
You can see m the damper and n the actuating cylinder. Note that it operates automatically with steam pressure on the steam chest supply pipe.
Correct, except about superheating increasing the pressure. Actually, the steam pressure remains the same as at the surface of the boilerwater but the temperature of the steam is increased by the amount of superheat that is added. While the boiler's "wet" steam temperature might be about 340 degrees or so, the superheater's "dry" steam temperature might be as much as 750 degrees! More heat means more energy and means more power. The heat is already available so its free power, except for the cost of the superheater units, etc. The superheated steam required special lubricants (ordinary petroleums would ignite) as well as the use of piston valves instead of the older "D" valves of the 19th Century. Technically, all self-actuating engines are really called "heat engines" as opposed to the manual or mechanical engines such as the Cotton "gin" engine which was powered by hand. Today, just about every engine is a heat engine as the main source of the energy is heat not animal, whether internal or external combustion, so no one uses the older designation of heat engine anymore. Any way that you can increase the heat, will increase the power, as long as you don't melt the engine. The desire for more heat is why racing cars use nitrous oxide fuel. It adds more available oxygen to the fuel mixture than the atmosphere can. Look what oxygen does to an acetylene torch. A somewhat similar motive was used in the last days of steam with the use of "overfire jets" with the extra bonus of reduced smoke due to better combustion, but that's another topic.