I have read references to a third steam cylinder located on the trailing truck or even on the tenders trucks of some steam locomotives. Can anyone enlighten me on this as to how it worked and where, when and by which roads it was used?[%-)]
Thanks, Tom
Hello Tom,
I think what you are describing is a booster engine. They typically had two small cylinders to provide starting effort before cutting out at around 30 MPH. Figure around 300 HP. Tender boosters were usually only used for yard locomotives, while trailing truck boosters were used on various railroad’s main line power, as long as it had a four wheel trailing truck.
Here is a cutaway view of one.
On roads, they were common only in North America, but I can’t tell you an all inclusive list.
Hope this helps,
NW
The C&O and PRR used them on a few locomotives also the CPRR, the NYC applied boosters to many of their Hudsons. Their use was on limited number of locomotives, those who did try them deemed them unnecessary for most of their needs.
There is a huge difference between a booster and a three cylinder locomotive. Boosters were auxiliary units which could be cut in or cut out as needed and usually found either on the trailing truck of the engine or on one or more of the trucks on the tender. A three cylinder locomotive would have a third cylinder between the drivers of the engine to increase steam pressure to the driver’s cylinders. Booster, three cylinder, two different things entirely.
Several months ago, someone provided a link to a manual on operation of boosters that was quite interesting.
The link showed them to be a plumbers night-mare and definately NOT very user friendly, but they worked. Quite common on SP Pacifics on the SF/San Jose run. (This was in the '40s and I was facinated but totally ignorant about their operation–but, finely, now I know)!
Tweedy
Boosters: New York Central’s Hudsons all had them. No K4 had them. The PRR Duplexes did not have them. The only PRR locos that had them were the “J” 2-10-4’s, a slightly modified C&O design. Most were not maintained and were removed before the J’s were retired, although some did keep them to the end around 1957.
The only really succesessful 3-cylinder USA locomotives (third between the other two, under the center of the smokebox) were the UP 9000’s, the 4-12-2’s. Excessive valve-gear and driving rod maintenance was normal.
Three-cylinder steam locomotives seemed to have the same problem as most poppet-valve equipped locomotives, they were oddballs and suffered from a lack of proper maintenance.
I would be curious to find out the track record of the grandest 0-8-0 of all, IHB’s three-cylinder U-4a’s.
Henry, I’m sorry, but I found your description to be somewhat unclear. Would it not be better to have described the third cylinder as being connected to the second driver axle (with the first driver axle having a crank in it so that the rod between the cylinder and the driven axle would clear the first axle).?
With the valve gear, along with the rod from the cylinder to its driven axle all inside, it was very difficult to reach any of the mechanism for maintenance, so three cylinder locomotives were not at all popular. Booster engines were more accessible, yet few roads had them on their engines.
A three cylinder locomotive has a third cylinder between the drivers of the engine taking low pressure steam and feeding the drive wheel cylinders with higher pressure steam. A booster is just a cylinder which can be cut in and out as needed and can be located on the trailing truck of the engine or one or more of the trucks on the tender. A three cylinder locomotive can in fact feed to a booster unit. If you are confused by this, then go to you library and find books on steam locomotives which would have diagrams and the same explanations.
Most 3-cyl engines in the US connected the inside cyl to the 2nd drivers-- was the MP 2-8-2 the only one that didn’t? But in England the 3rd cyl sometimes drove the lead drivers.
Dunno how many US engines had bent first driver axles. Not all, it seems.
In the US, usually no valve gear inside.
Probably the rest of you know better than to believe that. Webb compounds in England had one low-pressure cyl inside-- did anyone else’s engines do that?
Was BLW 60000 the only compound 3-cyl in the US?
Here is a reference to the only type of three cylinder (other than Shays) that I had heard of. http://www.steamlocomotive.com/3cylinder/
I do not understand how you can operate a cylinder without valve gear. The article also states that the UP 4-12-2 did not have a crank in the first axle. Some others, such as the engine developed for the Southern Pacific, did.
Henry, can you cite a reference that describes how a low pressure cylinder produces high pressure steam>
SO you are saying I am a liar? All of you better read some books on this topic and others pertaining to railroading before you start calling people out. If I am wrong, cite chapter and verse that will show how and where and why. Otherwise don’t say anything.
It has “valve gear”-- which in the US was usually the Gresley-Holcroft levers in front of the outside cylinders, on the pilot beam or whatever it’s called.
Any c\ylinder has to have valves and valve gear. ON USA three-cylinder locos the valves for the inside cylinder were generally operated by a gear motion derived from the two oustide cylinder’s valve-gear, rather than directly from drivers on either side. This was the case of the UP 4-12-2’s. I had forgotton about the Indiana Harbor Belt 0-10-2’s, and they could be called successful also. Also with derived moition for the inside valves.
Johnny, I don’t have to…just go to the library and find all the books on the subject. If you can’t do that, then don’t make comments to me about what I say. If you are too lazy to go to the library, then Google it or BIng it or search. You–and quite a few others here–ask questions and make ignorant statements then refuse explanations and directions to information and make derogatory remarks to us. I don’t like that and others have quit these pages because of that.
Henry, I am puzzled as to how you can consider my asking for a reference is equivalent to my saying that you are not telling the truth. I simply asked for information describing the workings of a cylinder that converts low pressure steam to high pressure steam; that is my understanding of your description; did I misunderstand what you wrote? Do you know of any site on the internet that describes such? Can you please give us the names of particular books that describe this?
All the information that I have seen, my sixty-five or so years of gaining information on the operation of railroads, has never had mention of such a mechanism, and I would be glad to learn how such works.
Thanks, Timz. I did find photographs of both the SP and UP three-cylinder engines, in Michael Swift’s Iron Horses (London, 2008, Compendium Publishing , Ltd.) The particular edition that I have lists Book Sales, Inc., Northfield Avenue, Edison, New Jersey, 08837 as being the source in this country.
There is one picture of an SP engine on page 164, and there are two pictures of the UP 9000, on pages 166 and 167. All three pictures show mechanism projecting from the front of the valve cylinders which, as you say, connects with the valve for the third cylinder There is no head-on view which might give more detail of the exterior workings. However, there must be mechanism beside the third cylinder to regulate the movement of the valve; would not this be considered a part of the valve gear? Also, there needed to be some means of converting the valve motion so that the motion of the inside valve is 120 degrees out of phase with that of the two exterior valves. Was this phase differential worked out in the exterior coupling? (I do not know if the SP valves were exactly 120 degrees apart as those of the UP were).
The inside valve is driven by its valve stem that extends forward and is driven by the shorter of the two levers on the pilot beam. No need for anything beside the inside cylinder.
Was intended to be; they say the center-cyl cutoff tended to be longer than the outside cyl due to play and the levers not being perfectly rigid.
We can’t expect exact, but it’s a good bet the three pistons were supposed to be front-dead-center at 120-degree intervals of driver rotation, and presumably the valves likewise. Since the center cylinder was inclined 9.5 degrees on the SP and UP engines it’s a good bet the inside crank was shifted 9.5 degrees from 120-120-120.
You have to read more books because most all railroads struggled with or tested three cylinder locomotives. In all my 70 years it has been part of the lexicon especially in written materials.
