User:Gatoclass/SB/Engines


 * Replacement headers: Connection mechanisms / Cylinder technologies / Cylinder orientation? / possibly also Propulsion methods. First two substitute for "Engines classifed by ... " because they are classified by both, right? Make necessary changes to overview section.


 * Nice overview of techs in P. dictionary - new section dealing specifically with triple, quad expansion etc., to finally fix linking problems!


 * Inclined/diagonal / High-pressure inclined (Southern US) / bell crank / geared beam/beam propeller


 * Propulsion methods: paddlewheels: sidewheel, sternwheel. Screw. Others?


 * Main sections: beam, return conrod, direct, cylinder techs


 * beam:


 * bell crank
 * grasshopper
 * side-lever
 * walking beam
 * geared beam


 * return conrod:


 * square crosshead
 * steeple
 * siamese
 * back acting


 * direct acting
 * oscillating
 * trunk
 * vibrating lever (half trunk)
 * diagonal (inclined)
 * high pressure (w rivers)
 * vertical


 * cylinder techs:


 * simple
 * simple expansion
 * compound
 * triple expansion
 * quadruple expansion
 * unaflow

with one end of each beam connected (via a shared overhead crosshead) to the piston rod, and the other attached via a connecting rod to a flywheel which in turn drove one of the paddlewheels. This arrangement (similar in some respects to the later side-lever engine) was dubbed the bell crank engine due to its somewhat similar appearance to the mechanism typically used at the time to ring church bells.

Bell crank
The world's first commercially successful steam-powered vessel was the North River Steamboat, designed by Robert Fulton and built in the United States in 1807 to operate on New York's Hudson River. The engine cylinder and air pump for this vessel were built in England by Boulton & Watt to Fulton's general specifications, while Fulton himself designed and built the mechanism for transmitting power to the paddlewheels. For this purpose, Fulton adapted an existing design, known as the bell crank or angular beam mechanism. In Fulton's versions of the type, the engine cylinder was upright, with the piston rod operating vertically above. The piston rod was secured to a horizontal crosshead, from each end of which a side rod extended downward vertically on each side of the cylinder. The side rods in turn were linked to a pair of large and heavy L-shaped beams, each secured at the right angle by a heavy pin upon which the beam could pivot. In Fulton's early engines of the type, the other ends of these beams were attached to their own connecting rod, which turned a separate crank on the paddlewheel crankshaft. In later versions, it appears that the ends of the two beams were instead connected to a shared crosstail, from which a single connecting rod extended to turn a lone crank. In either case, the basic design was very similar to that of the later side-lever engine, the main difference being that the beams of a bell crank engine are L-shaped instead of straight.

To offset the weight of the engine cylinder, Fulton extended the lower arms of the beams beyond the pivot points and attached counterweights. In order to try and smooth out the engine's operation (which in a single-cylinder beam engine tends to weaken at the top of the stroke) he had the crankshaft fitted with gears that operated large and heavy flywheels. These flywheels were reportedly very noisy in operation.

Fulton's bell crank engines were heavy and inefficient and it appears that the type was only ever built by Fulton himself, who installed it in just a handful of steamboats. In 1810, rival inventor Robert L. Stevens replaced the original engine in his steamboat Phoenix with a new design of his own, the crosshead engine, which quickly established itself as the standard engine type for early American steamboats.

Geared beam
In the 1840s, the screw propeller began to replace the paddlewheel as the preferred means of marine propulsion, as the greater efficiency of the screw results in much greater economy of operation. A marine screw propeller, however, needs to rotate faster than a paddlewheel in order to produce the same thrust, and boilers at this time could not safely produce pressures high enough to run engines at the appropriate speed, nor were the engines themselves designed to run at such speeds.

The obvious solution was to introduce gearing between the engine and the propeller shaft, so that one revolution of the engine produced multiple rotations of the screw. One of the earliest engine types to be so adapted was the old, slow-rpm beam engine, which could be mounted to engage, via the gearing, with the propeller shaft. These engines generally became known as geared beam engines, though a number of other names were employed, including beam geared, beam and geared, beam-propeller, beam screw and geared beam screw. Gearing was generally set at a ratio of 3:1 or more, so that one engine rotation produced three or more rotations of the screw.

Geared beam engines were mainly used through the decade of the 1850s, and mainly in British service, with some marine engineers preferring this type of engine for its ease of maintenance. Gearing presented well-known technical problems however, including noise, reduced efficiency, the difficulty of accurate machining, the tendency of the gears to get out of alignment, and gearing wear, so that such engines eventually fell out of favour in preference to other solutions.

Some of the last engines to mate the beam engine with the screw were able to dispense with gearing altogether, as engines and boilers were by this time sufficiently advanced to operate the engine at the same speed as the screw. Such engines were, however, generally regarded as anachronistic&mdash;since direct-acting engines were by this time widely available&mdash;and consequently, few were built.



High pressure (western rivers)
While the crosshead engine, and later the walking beam, became the dominant powerplants on steam vessels operating in the Eastern United States and later the West Coast, a very different type of engine came to predominate in the American South and Midwest&mdash;chiefly on the Mississippi and Ohio rivers and their tributaries (known collectively as the "western rivers"). Navigation hazards on the Mississippi in particular—which included sandbars, rapids, underwater snags, floating debris and narrow and twisting channels —greatly shortened the average life of a steamboat, and created a need for vessels built of the cheapest possible components and with the lightest possible draft. This led to the development of the so-called high pressure engine.

It was well known to engineers from an early date that high steam pressures allowed a smaller engine to generate the same power as a larger engine operating at a lower pressure, but in the early decades of steam navigation, high pressures were generally avoided because the relatively primitive boiler technology of the day created a greater likelihood of boiler explosions. On the Mississippi, however, the economic advantages of such powerplants were so compelling that they quickly came to eclipse safety concerns. The relatively short service lives of these vessels meant that the initial capital outlay had to be modest, and small, powerful high pressure engines were not only cheaper to build, but also lighter, allowing steamboats to take on more cargo and still maintain a light draft, necessary for avoiding sandbars and snags.

The high pressure engines on these western rivers steamboats generally operated at around 200 psi&mdash;much higher than that for a typical crosshead or walking beam engine from the same period. High pressure engines were horizontal or slightly inclined in cylinder orientation, and were direct-acting, with long connecting rods. The standard machinery layout came to feature forward placement of the boilers to offset the weight of the engines aft. Boilers were long and cylindrical and placed side by side longitudinally in the hull, and were usually between two and four in number, though some steamboats had up to nine. The placement of engines and boilers gives western rivers steamboats their characteristic appearance of two smokestacks forward and paddlewheels aft.

Since maneuverability was highly valued due to the need to avoid river hazards, the engines on the earlier steamers of this type usually drove sidewheels, with each wheel ideally having its own dedicated engine; this arrangement allowed the wheels to be readily run in opposite directions, allowing a steamer to essentially turn on its own axis. The same maneuver could be achieved in a sidewheeler with a single engine so long as each wheel had an independent shaft, but was more difficult to perform in a timely manner as it required manual decoupling. Sternwheels, by contrast, were widely rejected early on due to their lack of maneuverability, and were only used on the smallest and cheapest steamboats. This paradigm was reversed after the civil war with the invention of the, which gave sternwheelers the advantage. Because sternwheels were also better protected from river hazards, they thenceforth became the region's predominant steamboat type.

The great disadvantage of the high-pressure steamboat, as noted above, was the increased risk of boiler explosions, while the high pressures also meant that explosions when they did occur were very destructive. Serious boiler explosions on such vessels for many years consequently occurred with monotonous regularity. Authorities attempted to reduce the prevalence of such accidents by legally limiting boiler pressure to 150 psi (later revised to 175 psi) but since enforcement was lax, and Southern steamboats seldom even bothered with pressure gauges, such regulations had little effect. Improving boiler technologies eventually eliminated the problem, but not until many thousands of passengers had lost their lives or suffered serious injury.




 * high pressure sketch