Triplex (locomotive)
Encyclopedia
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
that divides the driving force
Divided drive (locomotive)
A divided drive locomotive is a steam locomotive that divides the driving force on its wheels by using different cylinders to power different pairs of driving wheels in order to give better weight distribution and reduce "hammer blow" which can be damaging to the track, or else to enable the wider...
on its wheels by using three pairs of cylinders rigidly mounted to a single locomotive frame
Locomotive frame
A locomotive frame is the structure that forms the backbone of the railway locomotive, giving it strength and supporting the superstructure elements such as a cab, boiler or bodywork. The vast majority of locomotives have had a frame structure of some kind...
. Inevitably any such locomotive will be articulated
Articulated locomotive
Articulated locomotive usually means a steam locomotive with one or more engine units which can move independent of the main frame. This is done to allow a longer locomotive to negotiate tighter curves...
. All the examples that have been produced have been of the Mallet
Mallet locomotive
The Mallet Locomotive is a type of articulated locomotive, invented by a Swiss engineer named Anatole Mallet ....
type but with one extra set of driving wheels under the tender.
Triplex classes
Baldwin Locomotive WorksBaldwin Locomotive Works
The Baldwin Locomotive Works was an American builder of railroad locomotives. It was located in Philadelphia, Pennsylvania, originally, and later in nearby Eddystone, Pennsylvania. Although the company was very successful as a producer of steam locomotives, its transition to the production of...
built three 2-8-8-8-2
2-8-8-8-2
Under the Whyte notation for the classification of steam locomotives, a 2-8-8-8-2 has two leading wheels, three sets of eight driving wheels, and two trailing wheels. Because of its length, such a locomotive must be an articulated locomotive. It is not longer than a normal articulated; the third...
locomotives for the Erie Railroad
Erie Railroad
The Erie Railroad was a railroad that operated in New York State, New Jersey, Pennsylvania, Ohio, Indiana, and Illinois, originally connecting New York City with Lake Erie...
between 1914 and 1916. One 2-8-8-8-4 was also built, for the Virginian Railway
Virginian Railway
The Virginian Railway was a Class I railroad located in Virginia and West Virginia in the United States. The VGN was created to transport high quality "smokeless" bituminous coal from southern West Virginia to port at Hampton Roads....
in 1916. This was class XA, so named due to the experimental nature of the locomotive.
There was also a proposal for a quadruplex super Garratt locomotive with a 2-6-6-2+2-6-6-2 wheel arrangement for South African Railways, but this was never built.
Usage
The purpose of the Triplexes was bankingBank engine
A bank engine or helper engine or pusher engine is a railway locomotive that temporarily assists a train that requires additional power or traction to climb a grade...
heavy trains over steep inclines, requiring high tractive effort
Tractive effort
As used in mechanical engineering, the term tractive force is the pulling or pushing force exerted by a vehicle on another vehicle or object. The term tractive effort is synonymous with tractive force, and is often used in railway engineering to describe the pulling or pushing capability of a...
, but low speed, over short distances.
The center set of cylinders received high-pressure steam. The exhaust from these was fed to the two other sets of cylinders, which were valved
Valve gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...
for low pressure. The right cylinder exhausted into the front set of low pressure cylinders, and the left into the rear set; this is also why the high pressure cylinders have the same diameter as the low pressure ones, whereas most mallet locomotives have much smaller high pressure cylinders. The front set exhausted through the smokebox
Smokebox
A smokebox is one of the major basic parts of a Steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler. The smoke then enters the smokebox, and is exhausted to the atmosphere through the chimney .To assist...
and the rear set exhausted first through a feedwater heater
Feedwater heater
A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system...
in the tender
Tender locomotive
A tender or coal-car is a special rail vehicle hauled by a steam locomotive containing the locomotive's fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so tenders are necessary to keep the locomotive running over long distances. A locomotive...
and then to the open air through a large pipe, which can be seen in the photo. Since only half of the exhaust steam exited through the smokebox, firebox draft (and thus boiler heating) was poor. Although the boiler was large (in line with contemporary two-cylinder and four-cylinder practice), six large cylinders demanded more steam than even such a boiler could supply.
With all six cylinders operating at their full pressure (which could not be sustained for very long), the Triplexes produced huge amounts of tractive effort
Tractive effort
As used in mechanical engineering, the term tractive force is the pulling or pushing force exerted by a vehicle on another vehicle or object. The term tractive effort is synonymous with tractive force, and is often used in railway engineering to describe the pulling or pushing capability of a...
(TE) that may have been the highest of any steam locomotives before or since. (Westing gives a figure of 160000 pound-forces (711.7 kN) in compound mode and seems to indicate that it was the largest TE for any locomotive up to the time [1914-1916]. See the Tractive effort
Tractive effort
As used in mechanical engineering, the term tractive force is the pulling or pushing force exerted by a vehicle on another vehicle or object. The term tractive effort is synonymous with tractive force, and is often used in railway engineering to describe the pulling or pushing capability of a...
article for other TE figures.) The Triplexes could also be considered the largest tank engines ever built since the tender had driving wheels as well and thus contributed to traction. The problem of variable adhesion on the tender unit was not a serious one, since pusher locomotives had frequent opportunities to take on additional fuel and water.