   #copyright

4-2-0

2007 Schools Wikipedia Selection. Related subjects: Railway transport

   The Chicago and North Western Railway's first locomotive, 4-2-0
   Pioneer.
   Enlarge
   The Chicago and North Western Railway's first locomotive, 4-2-0
   Pioneer.

   In the Whyte notation, a 4-2-0 is a railroad steam locomotive that
   consists of a 4-wheel leading truck followed by a single driving axle.
   This type of locomotive, often called a Jervis type, was common on
   American railroads from the 1830s through the 1850s.

   The equivalent UIC classification is 2'A.

History

   The first 4-2-0 built was the Experiment (later named Brother Jonathan)
   for the Mohawk and Hudson Railroad in 1832. It was built by the West
   Point Foundry based on a design by John B. Jervis. Having little else
   to reference, the manufacturers patterned the boiler and valve gears
   after locomotives built by Robert Stephenson of England.

   This had developed from the 2-2-2 design of his first Long Boiler
   locomotive, which he had altered to place two pairs wheels at the front
   with the outside cylinders between them to improve stability.

   A few examples of Stephenson locomotives were already in operation in
   America, so engineers did not have to travel too far to get their
   initial ideas.

   The design is a modification of the 0-4-0 design then common in
   America. The 0-4-0 proved to be too rigid for the railroads of the day,
   often derailing on the tight curves and quick elevation changes of
   American railroads. For the 4-2-0, Jervis designed a four-wheel leading
   truck under the locomotive's smoke box that swiveled independently from
   the main frame of the locomotive. The pistons powered a single driving
   axle at the rear of the locomotive, just behind the firebox. This
   design resulted in a much more stable locomotive that was able to guide
   itself into curves more easily than the 0-4-0.

   This design proved so effective on American railroads that many of the
   early 0-4-0s were rebuilt as 4-2-0s. The 4-2-0 excelled in its ability
   to stay on the track. But with only one driving axle, the locomotive's
   weight was spread over a small proportion of the powered wheels, which
   meant its total power was substantially reduced.

   One possible solution, patented in 1835 by Charles and George E.
   Sellers, caused the locomotive to tip upward while it was ascending a
   grade. This plan placed more of the locomotive's weight on the driving
   axle, but by reducing the weight on the leading truck, also made it
   more prone to derailments.

   A more practical solution, first put into production by Norris, moved
   the driving axle to a location on the frame in front of the
   locomotive's firebox. Cantilevering the weight of the firebox and the
   locomotive crew behind the driving axle placed more weight on the
   driving axle without substantially reducing the weight on the leading
   truck. However, Norris's design led to a shorter wheelbase, which
   tended to offset any gains in the tractive force on the driving axle by
   reducing the locomotive's overall stability.

   As the 1840s approached, and more American railroads were experimenting
   with the new 4-4-0 locomotive type, the 4-2-0 fell out of favour as it
   was not as able to pull a paying load on the railroad as the 4-4-0.

   4-2-0s were built into the 1850s, but their use was restricted to
   light-duty trains as most railroads by this time had found them
   unsuitable for regular work.
   Retrieved from " http://en.wikipedia.org/wiki/4-2-0"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
