More booster questions

[erikem]

Traditional DC generator & DC series motor electric drives were about 85% efficient, or about the same as the peak efficiency from the hydrokinetic drives. From what I understand, the electrical systems on the steam turbine electrics worked fine, but the performance of the boiler and steam turbine were disappointing. Using a once through steam cycle significantly reduces efficiency and air cooled condensers don't work very well in hot climates.

- Erik

[Paul Milenkovic]

I know there are all of these "what ifs", and it seems that well over a half century since the "dropping of the fire" in many places, the railroad industry has settled on electric locomotives where the traffic or local economic conditions justify it, and on Diesel-electric locomotives with power-electronic control of AC traction motors.

The electric drive introduces a lot of expense and complication to a locomotive, and it maybe it was a near thing that the Diesel electric caught on.  The steam electric certainly was tried but didn't get much acceptance.  Maybe coal dust and water leaks and electric motors with commutators didn't mix; maybe the electric drive added another 20% energy loss on the already inefficient steam cycle; a steam engine, with condensing in the case of the GE-UP steam turbine demonstrator -- plus electric drive -- was just "a bridge too far."

But what about hydraulic drive?  Is it really simpler or more efficient than electric drive?  There was a popularity of Diesel-hydraulic locomotives in Europe, but the K-M units tried in the U.S. were "roundhouse queens", but maybe they had (in steam loco designer L. D. Porta's words) bad detail design for the intended lugging service on U.S. mountain railroads?  That sort of heavy duty service is done by electrics in Europe?

But what about hydraulic drive.  You have hydrokinetic and hydrostatic.  Hydrokinetic is essentially the torque converter in the automatic transmission in your car, and generally speaking, hydrokinetic drives have comparable or even better efficiency than electric drives.  There is the problem of heat dissipation in heavy duty use (you can burn up the transmission in your car pulling too heavy a trailer; operators of the Budd RDC rail car were told that towing a second unpowered passenger car would void the warranty).  And whereas hydraulic locomotives had more sophisticated transmission in cars -- did some of the Mek-hydro units "change gears" by filling and emptying different torque converter units? -- the hydraulic locomotive may not have had the versatility in terms of flat torque over a wide speed range as the Diesel electric?

But what about hydrostatic drives?  Here, you have a variable stroke (generally piston-type) hydro pump and a piston-type hydro motor, and in theory, and that should be an ideal speed and torque matching transmission.  It is used a lot in light-duty farm tractors and in lawn tractors.

I am told the problem with the hydrostatic drive is in the friction of the piston-type pump and motors that kills the efficiency, especially at part load. 

But, coming back to the booster idea, does the entire locomotive need to use the same drive system?

There is some conflicting data on the efficiency of the classical rod-driven steam locomotive and where the losses are in translating indicated HP to wheel-rim HP to drawbar HP.  But let's just say we get the "cruise power" from the rod drive and we get the "starting or hill-climbing power (really high tractive effort but at low speed)" from the booster drive.

Does the booster need to be that energy efficient?  If you want high tractive effort at low speeds, the idea (in theory -- folks who fired these locos tell me boosters really sapped your boiler pressure) is that you don't need to be efficient.  You just need to not burn up your traction motors/hydraulic pumps.  But you can't tolerate a lot of parasitic friction with the drive not engaged once you exceed those starting/hill-climbing speeds.

But would a hydrostatic drive add a lot of cost and maintenance complexity to a steam locomotive?

[Overmod]

eagle1030

I know boosters would be used in addition to the main pistons, but was there ever a booster that could be used by itself?

Theoretically you might use a booster 'by itself', but it would not be particularly useful.

Remember that a booster has no throttle or cutoff adjustments of its own, and the early versions were specifically designed not to be reversible (even to be turned in reverse with the gears engaged).  The main engine's valve gear would have to be set just right for the engine to be 'pushed' without damage.  Note that the typical booster on trailing truck has VERY poor pushing geometry (it's not dynamically stable)

 

Say, moving an engine around a servicing facility or yard?

 

At low speed, you'd need a comparatively large mass flow of steam, none of which is providing draft to the boiler directly.  The very late 'high-speed' boosters could be provided with something other than a granny gear which would make proper use of the high effective starting torque of a steam motor for driving a comparatively light load... but is it really worth going to all that trouble just to have something that will hostle an engine in steam a little better than its own pistons could?

Solving the reverse and throttle issues are not insoluble; in fact, a workable solution might be adapted from the Kirchoff patent (for Franklin type D valve gear) which provides effective automagical 'variable cutoff' without the usual moving parts and proportional adjusting controls.  But it will never be the equivalent of clever use of the thrust reversers on DC-9s having to push back before the tug gets there...  ;-}

If not, would such a booster be economical, i.e., would it save a substantial amount of steam, or not enough to overcome the hassle and extra cost?

It would likely not save steam at all, considering that the blower and booster would both need to be operating simultaneously.  Directing the booster exhaust into the stack, please note, was NOT a popular or particularly successful option (of course it was tried in the earliest days of Super-Power, and the mere fact that you see booster exhaust routed all the way up to the boiler top behind the stack, but not actually used to induce draft, should caution you against putting booster exhaust into the front-end arrangements!)

A much better idea (I don't recall Porta saying anything about this, but if he didn't, he should have!) is to adapt a Lewty booster for use as a hostling engine.  The Lewty engine is used to drive a hydraulic pump, and the output to the 'booster truck' then becomes a matter of regulating the hydraulics or the Lewty-engine admission steam appropriately.  In those cases where there is also electric drive to the hydraulic pump, the locomotive can be moved when not in steam by simply applying a long 'extension cord' (in the same manner used to start up a forced-circulation boiler from cold before there is steam pressure to drive the circulation pumps...)

[NorthWest]

I would think that since you would need to heat up the boiler, add water, and have both crew on board, it would be no cheaper (and save no steam) to move only on a booster. Boosters were much harder to maintain as well.

(In modern EMDs, iirc one traction motor is able to run off batteries a short distance in shops. So, the idea is good, just not with steam.)

[eagle1030]

I know boosters would be used in addition to the main pistons, but was there ever a booster that could be used by itself?  Say, moving an engine around a servicing facility or yard?  If not, would such a booster be economical, i.e., would it save a substantial amount of steam, or not enough to overcome the hassle and extra cost?