Hi guys.
I borrowed a 1927 locomotive cyclopedia ( Truly amazing book) and was looking at trailing truck and tender booster engines. What I had noticed was that there was no way of disengagement of the driving engine from the wheels. When the booster is working steam is introduced to the cylinders just like the main drivers. When steam is cut the wheels and reciprocating machinery is still moving as long as the wheels are turning. Wouldn't that be a tremendous drag on the locomotive? You would think there would be some sort of clutch or sliding gear set to disengage the engine? Looking at the parts breakdown there appears to be nothing to keep the piston and rods from moving while the wheels turn. I can see why they were not very popular.
Pete
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I started with nothing and still have most of it left!
IIRC this same question came up maybe a year ago, you could do a search of the forums to see. Anyway, seems to me the concensus was that no, it had virtually no drag effect. Apparently the relative unpopularity had more to do with maintenance problems.
A steam locomotive that wasn't under power would roll pretty freely despite having cylinders and siderods. I recall reading somewhere that when roller bearings came along engines became so free-wheeling that 2-3 men could move even a big engine just by pushing on it. Frank King in one of his books noted that the DM&IR almost lost one of their first Yellowstones into a swamp, because it started to roll down a track that everyone had always thought was flat so they didn't bother to tie it down. Turns out it had a tiny grade to it that was enough to get the big engine rolling.
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This book shows no rocking or idler gears on the booster engines. Maybe later than 1927 the gear train was added?
I'd say it's a safe bet trailer-truck boosters always had the idler gear, so they could be cut out. The 1924 Franklin booklet so describes them. Dunno whether that applies to tender boosters as well-- maybe any engine that had a tender booster was thereby limited to 20 mph?
Thank You.
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It is off topic, but I hope tolerable....congratulations on your first grandchild, locoi1sa.
selectorcongratulations on your first grandchild, locoi1sa.
Thank you. She is a real doll.
Boosters did mechanically disconnect from the trailing truck wheel to eliminate unneeded wear and tear. In certain applications boosters made a lot of sense. Look at the typical 4-8-4. There you have an engine with a large, powerful boiler, but limited adhesion due to only 4 drive axles. At low speeds, it would be impossible to apply the boilers full output to the rail. The higher the boiler pressure, the worse it got at low speed because you are applying more force to the wheels with no increase in adhesive weight.
GP40-2 Boosters did mechanically disconnect from the trailing truck wheel to eliminate unneeded wear and tear. In certain applications boosters made a lot of sense. Look at the typical 4-8-4. There you have an engine with a large, powerful boiler, but limited adhesion due to only 4 drive axles. At low speeds, it would be impossible to apply the boilers full output to the rail. The higher the boiler pressure, the worse it got at low speed because you are applying more force to the wheels with no increase in adhesive weight. I know Ross Rowland was a huge fan of boosters, first with the 2101 and later with the 614. He told me that the booster more than doubled the DBHP on the 614 below 20 MPH. This was played out during a 614 Chessie steam trip where he marched a fully loaded 26 car passenger train (with a lot of older heavy weight equipment in the consist) right up the infamous Sand Patch Grade with no helpers and no slipping of the main drivers. Any other 4-8-4 with out a booster wouldn't have made it halfway up that grade with that much tonnage in tow.
I know Ross Rowland was a huge fan of boosters, first with the 2101 and later with the 614. He told me that the booster more than doubled the DBHP on the 614 below 20 MPH. This was played out during a 614 Chessie steam trip where he marched a fully loaded 26 car passenger train (with a lot of older heavy weight equipment in the consist) right up the infamous Sand Patch Grade with no helpers and no slipping of the main drivers. Any other 4-8-4 with out a booster wouldn't have made it halfway up that grade with that much tonnage in tow.
This point is not to be taken lightly. The horsepower produced by the typical booster engine was quite modest, but it was produced at a very low speed. (The horsepower of a 4-8-4 at low speed was also quite modest.) So even a few hundred horsepower, geared down to be applied at a speed of five miles per hour, supplied a substantial boost in tractive effort.
It's also the reason the booster had to be disconnected above a very slow speed. As the locomotive speed increased, the effectiveness of the booster rapidly decreased. The tractive effort boost provided dropped off rapidly because the engine simply couldn't be supplied with steam fast enough, nor could it withstand the high revs and piston speeds. The locomotive did worse with the booster connected above a certain very low speed.
Think about a loaded tractor trailer lugging up a steep grade. In low gear, the diesel behaves much like the booster engine. Not much speed but lots of tractive effort. On the flat, flooring the pedal while keeping the transmission in first gear would result in the engine soon exceeding redline and experiencing utter destruction. The booster lacked the transmission of a diesel truck, so was useful only at very low speeds. Then it had to be disconnected.
My understanding has been that the booster was meant to add to the tractive effort in order to get the bearings down the length of the train moving, and thence to get the train up to a minimal speed such that the trailing tonnage could be propelled to higher sustained speeds solely by the horsepower developed by in the cylinder saddle available at the time of cutting off the booster. Even if a typical booster only provided another 10k lbs of tractive effort, and the Y's did much better, that isn't something to decline if you know the booster will get a revenue train to the point where the engine can 'take it from there'.
-Crandell
Can anyone imagine a single Genesis unit attempting that. Can you say "French-fried traction motors"? I knew you could!
I don't know where the claim of doubling the draw-bar HP comes from -- the main cylinders are driving the 4 main wheels at pretty much the traction limit, and a booster engine is driving one trailing axle on the rear truck at a somewhat lower tractive effort per axle (they had to do it that way, otherwise that booster axle would be slipping all the time on account of the single-axle vs average-of-coupled-axles adhesion limits), and at whatever speed, HP = tractive effort in pounds X speed in feet per second X conversion of foot-pounds per second into HP. That means at any speed, the contribution of the booster is in proportion to tractive effort on the boosted axle, and I can't see it being close to half the total tractive effort.
Don't know the steepness of the Sand Patch Grade, but from the weight on drivers (plus booster) plus the weight of the train, that must have been some trick to get that train over the top with one locomotive -- a very judicious hand at throttle, reverser, and sander, and perhaps a lack of judgement in the brain to attempt this given the start of slipping means tying up that line for hours doubling the train or waiting for a push. On the other hand, it seems you could push a steam locomotive without fear of burning it out.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicCan anyone imagine a single Genesis unit attempting that. Can you say "French-fried traction motors"? I knew you could! I don't know where the claim of doubling the draw-bar HP comes from -- the main cylinders are driving the 4 main wheels at pretty much the traction limit, and a booster engine is driving one trailing axle on the rear truck at a somewhat lower tractive effort per axle (they had to do it that way, otherwise that booster axle would be slipping all the time on account of the single-axle vs average-of-coupled-axles adhesion limits), and at whatever speed, HP = tractive effort in pounds X speed in feet per second X conversion of foot-pounds per second into HP. That means at any speed, the contribution of the booster is in proportion to tractive effort on the boosted axle, and I can't see it being close to half the total tractive effort. Don't know the steepness of the Sand Patch Grade, but from the weight on drivers (plus booster) plus the weight of the train, that must have been some trick to get that train over the top with one locomotive -- a very judicious hand at throttle, reverser, and sander, and perhaps a lack of judgement in the brain to attempt this given the start of slipping means tying up that line for hours doubling the train or waiting for a push. On the other hand, it seems you could push a steam locomotive without fear of burning it out.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
oltmanndAt these low speeds, the boiler can make much more HP than the steam engine can use, so, if I increase the number of driving axles by 75% (from 4 to 7) by employing a booster, I should be able to increase my drawbar HP by the same amount. "Double" and "below 20 mph" are smallish exaggerations, I think.
A booster would be far more useful if it could power an additional 3 axles. My understanding of them, however, is that they were placed cylinders-pointed-rearward off the last axle of the trailing truck, and as such, they powered at most one axle.
Some tender boosters had siderods, although it had been remarked that siderods on the smallish tender truck wheels limited them pretty much to yard or transfer service on account of speed restrictions.
The remark that "boosters ate steam" earlier in this thread is one I believe. If the knowledge of locomotive firemen has been passed down to our generation through oral tradition, and if they guys whose job it was to keep steam up had experience with boosters, those things must have contributed to high steam consumption under heavy load.
A person has to figure that when a steam locomotive is at max tractive effort, the efficiency with which steam is used goes way down because one is probably operating close to max cutoff, not doing expansive working of the steam in the cylinders to optimize efficiency. A Northern at max tractive effort and low speed could be close to the steaming capacity of the boiler even if the DBHP was at the left-hand shoulder of the curve, and then to throw on the booster, that could keep the fireman on his toes.
A booster may even be set to a fixed and perhaps steam-eating high cutoff as it is only used sparingly at high tractive effort situations anyway. But as to a "booster eating steam", I am also wondering if adding the booster was a "straw that broke the camel's back" situation with regard to one more load that maxes out the boiler rather than the booster being less efficient than, say, the main cylinders operated at near 100 percent cutoff.
Maybe one more factor with the steaming problem under booster operation is the "Triplex effect." Not only does the booster use yet more steam, but it discharges exhaust steam elsewhere but up the main chimney. I am thinking that the exhaust of the booster goes down the downward pointing stovepipe doodads that you see coming out the trailing trucks of the locomotives in question. As the booster consumes steam but does not contribute to boiler draft, as did the entire 4-axle tender engine on the Triplex, one can see where the fireman has their work cut out maintaining the fire for enough steam.
As to the general remarks about boosters being "high maintenance", any appliance or gadget will add to maintenance, but the question is what you get for it. One knock on boosters is the maintenance problems of flexible steam connections, but Mallets, simple articulateds, and others all had flexible steam pipes. If you need the number of powered axles, what is more cost effective, a 4-6-6-4 Challenger or a 2-10-4 Texas with a trailing axle booster? They both require a flexible steam connection.
So ultimately, the question is can you get away with a straight Northern, a booster-equiped Northern, a booster-equiped 2-10-4, or do you need a Challenger. If you go with a straight Northern, then do you need to hook on to a helper for a ruling grade? If the added maintenance of a booster obviated the need for an articulated locomotive or a helper, than the money is well spent, that is unless boosters were that badly designed that they needed all kinds of work on them.
The last thing I have always wondered about boosters is that they are a kind of steam-powered traction motor, and why didn't people come up with locomotives where every axle was powered by a booster engine? Actually, there were rare examples of such a thing -- I think they had a high-speed gear-driven locomotive in Germany to test this idea. Maybe it is a question of when steam closed up shop and went home -- if it had stuck around a while longer, perhaps locomotive designs would have gone in that direction.
Paul MilenkovicoltmanndAt these low speeds, the boiler can make much more HP than the steam engine can use, so, if I increase the number of driving axles by 75% (from 4 to 7) by employing a booster, I should be able to increase my drawbar HP by the same amount. "Double" and "below 20 mph" are smallish exaggerations, I think. A booster would be far more useful if it could power an additional 3 axles. My understanding of them, however, is that they were placed cylinders-pointed-rearward off the last axle of the trailing truck, and as such, they powered at most one axle.
This has turned into an interesting conversation.
Yes, there were steam locomotives where every axle was drived by what amounted to a booster engine. One example was the shay. It could pull like crazy with the limitation that speed was limited to less than 15 mph, and that only if one wanted to overhaul the cylinders soon. More like 8 or nine mph was a realistic operating limit.
As far as boosters increasing the number of driven axles, a trailing truck never had more than one axle driven by the booster. This was true for a Northern type as well. So for a Northern, the weight on drivers might increase by 20%, but typically the increase would be less, more like 10 to 15% because the weight on the trailing truck axles wouldn't be as great as that on the drivers. A typical booster engine would increase tractive effort by about 10,000 to 12,000 lbs, and that only at low speed.
Now for a Northern, tractive effort produced by the main engine could remain at a peak much higher than the 5 miles per hour of a booster's peak tractive effort, precisely because the large drivers and valves of the main engine didn't restrict steam flow at higher speeds, and the boiler could produce all the steam the engine needed. The booster did eat steam at high speeds and for diminishing returns, so it would be cut out pretty early.
Remember that one characteristic of a steam locomotive is that, unlike a diesel-electric, it can be overloaded and produce more than it's rated power. The boiler can be overfired and produce more steam than it would at its best efficiency point. Lots of black smoke and unburned carbon up the stack, but lots of steam. A diesel couldn't do that. The locomotive had a horsepower limit set by the ability of the prime mover to convert diesel fuel to ponies. Hence the old adage that a steam locomotive could pull any train it could start, but a diesel could start a train it couldn't necessarily pull (being limited by the time rating of the traction motors.)
I like steam engines a lot, but I have to face the fact that they do suffer from a basic limit of adhesion in most of their forms. With only about half of their weight on their drivers, many steam designs were adhesion limited rather than horsepower limited. Exceptions included the afore mentioned shays and other geared engines and certain of the articulated such as the N&W Y types that could generate enough tractive effort (about 150,000# working simple) to pull trains in two.
About swiveling joints for boosters, these really weren't the big source of maintainence headaches they have been made out to be. These joints were easily accessible and in later days as better materials and designs were incorporated they were pretty trouble free. But the engine itself and its associated gearing were located inside the frame of the trailing truck (or inside the frame of the tender truck, perhaps worse. This is where the maintenance headaches would arise.
The exhaust from trailing truck boosters was not simply vented to atmosphere, but was routed to the main stack. Hence the two swiveling connections on the trailing truck, one on each side. One supplied live steam for the engine and the other carried exhaust steam to the stack. You can see a rather detailed drawing of all this taken from the 1922 Locomotive Cyclopedia by googling "booster engine" and looking at the wikipedia page.
Alan Robinson it can be overloaded and produce more than it's rated power.
When railroads tested their engines' drawbar horsepowers, and drew a power vs speed graph that peaked at 5000 dbhp at 40 mph, did that mean the engine could actually produce 6000? 7000? 8000? dbhp at 40 mph? If so, shouldn't that info appear on the graph somewhere? Seems relevant.
I haven't read a 1927 Locomotive Cyclopedia, but I do have a 1925 Locomotive Cyclopedia and it contains a detailed description of steam locomotive boosters.
On page 547: "The Locomotive Booster is a simple two-cylinder steam engine mounted on a cast steel bed plate. This engine is geared to the trailer axle through an idler gear. This (idler) gear is automatically engaged as required (for booster operation) and (automatically) disengaged when the power of the Booster is no longer needed". The answer then is that the booster steam engine "turns" only when it's power is needed, otherwise it is automatically disenegaged and, as today's truck drivers might say, it is in neutral and not turning.
Figure 1245 in the 1925 Locomotive Cyclopedia: "The Locomotive Booster" (p. 547) is an excellent cut-away view of a typical locomotive booster with all major components identified, including the Clutch Cylinder, the Idler Gear Rocker and the Idler Gear. From this is it fairly obvious how the engaging and disengaging is accomplished. And yes, the exhaust steam from the booster engine was directed to the smoke box at the front, where it joined the exhaust steam from the engine's (main) cylinders in the nozzle, thus adding to the draft.
Certain of the statements regarding the power available from a booster seem a bit ambitious. Turning to the Model Railroader Cylopedia I, Steam Locomotives, p. 199 the New York Central class J3a Hudsons, it reports that these steam locomotives could develop 53,960# T.E. without booster and 66,060# T.E. with booster. .That would put each of the three driving axles at 17,987# T.E. and the one axle powered by the booster engine at 12,100# T.E., or about 22% of the total T.E.
As to the stories about the boosters using a lot of steam: probably true. Not all that difficult to run a locomotive's boiler at -- say -- 80% capacity (true, ya gotta work for it !!) but to have to go up another 22% to 102% ... that's a whole 'nother story !!!!!
wccobb Model Railroader Cylopedia I, Steam Locomotives, p. 199 the New York Central class J3a Hudsons, it reports that these steam locomotives could develop 53,960# T.E. without booster and 66,060# T.E. with booster.
Yes
It sure nuff does-- wonder where they got that. Cylinders were 22-1/2 by 29, drivers 79, pressure 275 initially, so main-engine TE calculated in the usual 85%-MEP way comes out 43440 lb. No doubt that's the figure that appears in other books.
I wonder if all trailing-truck boosters had the same size cylinders-- probably so? Wonder how much variation in the wheel diameter-- and did they use different gearing for different locomotives with different boiler pressures?
oltmannd.85 x 275 x 11.25^2 x 3.1415 x 2 x 29 / 79 = 68,200# What am I doing wrong?
Two things. The "rated tractive effort" may be based on 70 % cutoff (are you using 85%?), and there may be assumption about pressure drop between boiler and cylinder inlet owing to whatever restrictions in the steam passages, valves, may occur.
Paul Milenkovic The "rated tractive effort" may be based on 70 % cutoff
When we calculate nominal tractive effort, we want the average thru a turn of the drivers, not the peak TE when the cranks are at their strongest position. So we assume the mean effective pressure in the cylinder is 85% of boiler pressure (which presumably includes an allowance for the slightly-smaller area on the back of the piston) and calculate the work done in one stroke of the piston and equate it to the work done at the wheelrims during half a rotation. So pi appears twice, and the two of them cancel out.
It comes out 0.85 times boiler pressure, times bore squared, times stroke, divided by driver diameter.
Paul MilenkovicThe last thing I have always wondered about boosters is that they are a kind of steam-powered traction motor, and why didn't people come up with locomotives where every axle was powered by a booster engine? Actually, there were rare examples of such a thing -- I think they had a high-speed gear-driven locomotive in Germany to test this idea. Maybe it is a question of when steam closed up shop and went home -- if it had stuck around a while longer, perhaps locomotive designs would have gone in that direction.
Actually, the B&O did. It was to be called W1, and it was a "4-8-4" that used 16 steam motors (4 per axle) to power the drive axles. The locomotive would have had 92 power strokes per revolution, produce 72, 500 lbs TE, have a huge water tube boiler operating at 350 PSI. It was calculated to produce in excess of 5000 DBHP at 100 MPH. Due to the financial crisis of the Great Depression and the outbreak of WW2, only design work and testing of components took place at the B&O shops. The projects was discontinued with the advancing technology of the D-E locomotive.
Paul MilenkovicA booster would be far more useful if it could power an additional 3 axles. My understanding of them, however, is that they were placed cylinders-pointed-rearward off the last axle of the trailing truck, and as such, they powered at most one axle. Some tender boosters had siderods, although it had been remarked that siderods on the smallish tender truck wheels limited them pretty much to yard or transfer service on account of speed restrictions.
I recently ran across a picture of a Southern Railway locomotive with what looks like a running gear under the tender - presumably for Saluda. This is on page 570 of the October 1917 issue of Popular Science - available on Google books - be forewarned that navigating to that issue is non-trivial.
Prince says SR had eight? engines with those drivers under a tender-- from the pic I can't make out whether the tender engine was reversible (which an ordinary trailer-truck booster isn't). They only claimed 8000+ lb TE from the tender engine, initially anyway.
Paul Milenkovic A booster would be far more useful if it could power an additional 3 axles. My understanding of them, however, is that they were placed cylinders-pointed-rearward off the last axle of the trailing truck, and as such, they powered at most one axle. [snip]
I'm recalling that there was an 0-8-0, 0-10-0, or 0-10-2 with a leading tender-truck booster that had siderods to link both axles together mechanically. I seem to recall that it was a DM&IR 0-10-2 locomotive, but it could have been an IHB instead.
- Paul North.
EDIT: I'm now pretty sure it was the ex-Union RR 0-10-2's, which then went to the DM&IR - though somewhere along the way, the boosters were removed. But I'm having trouble finding a decent photo of one . . .
In the meantime, here's the link to a photo of a 2-8+8-2 Mallet-articulated with 2 boosters on the tender trucks - each of them with siderods !
http://spec.lib.vt.edu/imagebase/norfolksouthern/full/ns966.jpeg
Supposedly it's an N&W Y-2 class, but I can't confirm or refute that one way or the other. - PDN.
Linked here is a photo of an N&W Y-3 Articulated Loco : http://spec.lib.vt.edu/imagebase/norfolksouthern/full/ns966.jpeg
(Both tender trucks are booster engine equipped!)
The discussion has centered around mostly trailing truck ( under the locomotive) booster engines. To be honest, til this thread I had always thought that locomotive boosters were set under the bunker end of a tender and its presence was always anounced by a set of side rods connecting the axles. The i discovered this link to Delaware and Hudson Steam locomotives and found some of their booster were on the rear tender truck and the side rods were the give away. Here is that link:
http://www.dself.dsl.pipex.com/museum/locoloco/USAhp/USAhp.htm
(Be aware some of these engines are not close to being ordinary looking! steam locomotives.)
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