Steam locomotive boosters

[Paul Milenkovic]

Can anyone fill me in on steam locomotive boosters? That notorious King article last summer took on Super Power steam for having too-tall drivers and too much weight on unpowered axles. Some Super Power locomotives had booster engines on the 2-axle trailing trucks supporting those big fire boxes, but the boosters were regarded as maintenance trouble.

How did the boosters work? Did they cut out at some speed? Did they have an overrunning arrangement where the booster engine could be stopped and let the wheels turn? Or did the booster engine turn with the wheels at all speeds? Was the booster a gear-drive arrangment like a Heisler or a Shay, or was it some kind of inside rod work? Did the boosters work at fixed valve cutoff? What kind of valves and valve link did they have?

I have been thinking about the Super Power high-drivered locomotives, and I have been wondering what the problem is with high drivers if they could produce enough tractive effort. It occured to me that based on the principle of mechanical advantage, the high-drivered locomotive may go through a lot more steam operating at cutoffs required to produce high tractive effort at low speeds (hill climbing) -- Super Power locomotives had the big fire boxes to supply the steam, but I am wondering if they went through a lot of coal and water to supply that steam. The advantage of the clunky Mallet is that it could operate at high expansion, even at high tractive effort, saving on coal and water under heavy pulls.

How about this kind of arrangement -- a 4-8-8 locomotive: 4-wheel leading truck for high-speed stability, 8-wheel rod-driven driver set, and 8-wheel trailing truck with a booster --- kind of a 3/4's Mallet. The eight-wheel trailing truck would leave ample room for a deep fire box. The trailing truck would be motored only at lower speeds for hill climbing and/or train starting and initial acceleration. The trailing truck would be motored through a gear-driven engine that would be uncoupled from the wheels at high speeds through a free-wheeling arrangement. The trailing truck booster engine would be the low-pressure Mallet-style expansion stage to the high-pressure main engine. The locomotive would operate as a simple engine on 8 drivers at high speed, as a compound engine on 8 drivers and 8 booster-truck wheels at low speeds. As to the booster being the low-pressure engine, you could have a high-speed engine through a gear drive providing the required cylinder flow rates, and this engine would cut out at high train speeds so that the booster engine would not overspeed.

Would something like this work?

[daveklepper]

I leave it to others to evaluate your proposal and get to the technical nitty griity on this, but yes boosters where like mineature locomotives in their own right with one or to cylinders, valve gear, rods, etc. They were cut out above a certain speed, 12, 15, 20 miles an hour depending on the locomotive. They were a maingt\tenance item, which is why during WWII, when Pennsy copied the C&O 2-10-4 they left off the booster.

[M636C]

Paul,

The problem with your proposal is fairly simple - look at a N&W 2-8-8-2 and its huge leading low pressure cylinders, and think about fitting them (or any number of cylinders with that volume) under the firebox.

It might be difficult to get a good balance in cylinder sizes for any type of compound that will essentially be a simple most of the time. You don't want the main cylinders to be penalised by excessive back pressure from the low pressure cylinders right at the moment you need the greatest tractive effort.

Most locomotive boosters only drove the trailing axle of the trailing truck. The only locomotives with coupled booster axles on a trailing truck that come to mind are the Norwegian State 2-8-4s and some English (LNER) 0-8-4 tank locomotives used as hump shunters.

Remember that if you couple the trailing truck wheels, they stay coupled even when the booster is uncoupled, adding to rolling resistance and requiring carefully matched diameters.

A reasonably successful locomotive using the principle you suggest but much more complex in mechanical design was the German State Railways class T38. This was a fairly large, medium wheel 4-6-0, originally Prussian State class P8, rebuilt with a condensing tender that contained an exhaust steam turbine driving three coupled axles under the tender. the use of a condenser reduced the back pressure to the level of normal operation, and the additional power was obtained with little loss in the original engine.

The T38 was as good in service as the largest "pacific" type, and regularly hauled more than the standard class 38. The cost and maintenance were too high, and only one was built.

This was often the fate of "improvements" to basic steam locomotives. The improved performance was obtained at an uneconomic cost.

Peter

[daveklepper]

Was the T38 the very first steam turbine locomotive? I recall that there was a postwar Pennsy turbine, I think their only 4-8-4, where the turbine drove driving wheels directly, not as in the N&W and C&O and UP (oil) experiments, through electric drives.

[feltonhill]

PRR J1 and J1a's all had boosters. Check any photo, the typical piping is back there under the cab. They were rated at 93,750 lbs TE for the locomotive and 15,000 lbs for the booster, a total of 108,750 lbs. PRR experimented with boosters on a few individual locos (IIRC L1, K4, T1 6111), but the J1 was the only class to be universally equipped.

PRR did have a direct drive turbine #6200, Class S2, a 6-8-6 as built in 1944. It was originally intended to be a 4-8-4 but weight got too high during the design process and additional axles were added.

[Paul Milenkovic]

WIth respect to steam there are the views 1) steam didn't reach the fulfillment of the technology, because there were a lot of ideas that were untried or perhaps not given a chance (poppet valves, low back pressure exhaust, condensors, water tube boiler, turbines, fluidized-bed/gas-producer fire box, cranked axle 3 and 4 cylinder drives, compounding of various kinds), 2) all of these enhancements were tried and found wanting, and there are good reasons for their deficiencies.

As a railfan and person interested in the history of technology, I find it fun to speculate on the what-could-have-beens and what-could-be's. I also think that speculation is productive -- no one is going to bring back the Curtis-Wright 18-cylinder turbocompound radial aircraft engine, but the turbocompound system ran at unusually high thermal efficiency, and perhaps there is a way to adapting it to a fuel-efficient automobile -- perhaps the new magnet technology will be electric drive the way to go to match the elements of the turbocompound engine.

As to steam, the Mallet of compound expansion in two engines with the high pressure engine fixed and the low-pressure engine movable was eminently successful. The Mallet was regarded as restricted to low speeds on account of the suspension of the front engine (a problem solved by the simple-expansion Challenger), and the large LP cylinders.

My speculation was, could you have a Mallet, but with mismatched engines -- operate the LP engine only at low speed for hard "pulls" and operate simple expansion at high expansion ratios at high speeds. The concept would be akin to the "road slug" on a Diesel where some of the powered axles would only kick in at low speed. I thought of the notion of the booster engines that were low-speed only, although I guess simple-expansion systems.

The LP engine needs a lot of flow volume, and one way to get it is with oversized cylinders. The other way would perhaps be a geared engine or a low-drivered rod engine that would operate at high speeds but would cut out at locomotive speeds that would cause it to overspeed.

The info on boosters is enlightening -- the idea that they powered at most a single axle on account of the complication and rolling resistance of powering multiple axles -- the single vs multiple axle drive enters into Diesel multiple unit cars and related applications.

[M636C]

There were a number of steam turbine experiments in Europe in the 1920s, both condensing and non-condensing. The best reference is a Swiss book in the German language "Dampflokomotiven und Dampfteknik" by Wolfgang Stoffels. It lists as far as is known, every high tech steam locomotive experiment, and many unbuilt proposals.

You would be surprised how few ideas have not yet been tried! If you can imagine it, someone has tried it! (Or at least, patented the design).

I should point out that coupled boosters were used in the US under locomotive tenders, mainly coupled to switchers, but I think but the D&H triple expansion 4-8-0 had a coupled booster, driving two axles of a three axle truck, if I recall correctly.

There is a turbo-compound aero engine in the Franklin Institute in Philadelphia, which I've examined. Being a radial, it had three turbines spaced out at 120 degrees around the circumference of the engine on shafts parallel to the connecting rods, geared to drive a single centrifugal compressor at the back behind the propeller shaft. Check that out while you go to look at the Baldwin 4-10-2 #60000. I'm not surprised that the turbo compounds rarely made a return trip from Los Angeles to Sydney Australia without one of the four failing! The JT3Cs on the early 707s burnt so much fuel that QANTAS had special versions built with a ten foot plug TAKEN OUT to get trans Pacific range. But they just kept running, so everybody was really pleased. Then the JT3D turbofan arrived and they were just great. John Travolta has one of the ex QANTAS short 707s, built with the JT3D engines, and he flies it everywhere.

The big problem I see with Paul's partial use of exhaust steam is how you convince it to go through an engine if the remainder is exhausting to atmosphere. I know that this is done with feed water heaters and exhaust steam injectors, but they work at very low pressure. If the steam is given two optional routes, one with lower back pressure than the other, it will tend to follow the easier route. You might be able to direct the exhaust from one cylinder all to the booster, but might need to have a variable (in area) exhaust nozzle to get adequate draught on the fire with only half the exhaust steam.

Peter

[daveklepper]

Possibly my impression about the Pennsy's J's 2-10-4's came from later days when the boosters were not maintained any longer. But thanks for the correction, and I did come to remember independently that the S-2 was a 6-8-6. I remember the Lionel model. Any information you can give about the actual use of the S-1 (the 1939 6-4-4-6 Loewy streemliner) and the S-2 in service would be most interesting.

[M636C]

You're asking me? From my reading, both the S-1 and S-2 were used in passenger service between Crestline Ohio and Chicago Illinois. The S-1 was used through WWII but was withdrawn fairly early post war with the arrival of the T-1s (and more importantly, the EMD E-7s). The S-2 was regarded as more of an experiment, and there is a posed photo of it on Horseshoe Curve (the S-1 probably wouldn't fit through the Gallitzin tunnels, and the S-2 would have been a tight fit) but I thnk it did some work on passenger trains Chicago - Crestline in the late 1940s. To both have the letter "S" the PRR must have regarded the two wheel arrangements as the same.

Peter