Triplex locomotive

Last updated
Erie 5016 in Exeter, PA ERIE 28882.jpg
Erie 5016 in Exeter, PA
The Matt H. Shay 2-8-8-8-2 locomotive Erie Railroad Matt H. Shay 2-8-8-8-2 locomotive.JPG
The Matt H. Shay 2-8-8-8-2 locomotive
The only 2-8-8-8-4 triplex locomotive ever built 28884.jpg
The only 2-8-8-8-4 triplex locomotive ever built

A Triplex locomotive is a steam locomotive that divides the driving force on its wheels by using three pairs of cylinders rigidly mounted to a single locomotive frame. Inevitably any such locomotive will be articulated. All the examples that have been produced have been of the Mallet type but with one extra set of driving wheels under the tender.


Triplex classes

Baldwin Locomotive Works built three Triplex locomotives for the Erie Railroad between 1914 and 1916. [1] The first was named Matt H. Shay, after a beloved employee of that road. [1] It could reportedly pull 650 freight cars. [2] The Triplexes were primarily used as pushers on grades requiring helper locomotives. Slow moving, the Triplexes were not considered highly successful, and no more were built for Erie. The Erie Railroad scrapped their Triplexes from 1929, 1931, and 1933. [3]

Another very similar designed Triplex was built by Baldwin as a 2-8-8-8-4 for the Virginian Railway, as No. 700, in 1916. This was class XA, so named due to the experimental nature of the locomotive. The 2-8-8-8-4 was unsuccessful because it only made a maximum speed of 3–5 miles per hour and had high maintenance costs. The XA was sent back to Baldwin Locomotive Works in 1920 to be converted to a 2-8-8-0 and a 2-8-2. These two engines were in service until 1953. Neither of the two engines were preserved.[ citation needed ]

Baldwin filed a patent application for a quadruplex locomotive in 1913. 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. [4]


The purpose of the Triplexes was banking [3] heavy trains over steep inclines, requiring high tractive effort, but low speed, about 10 mph, over short distances.[ citation needed ]

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 for low pressure. [3] 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, making the engine a 2 to 1 compound, whereas most mallet locomotives have much smaller high pressure cylinders. The front set exhausted through the smokebox and the rear set exhausted first through a feedwater heater in the tender 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. [3] The Erie locomotives always operated compound and did not have starting valves which would have put full pressure on all 6 cylinders, even so the Triplexes produced huge amounts of tractive effort (TE) that may have been the highest of any steam locomotives before or since. (Westing [3] gives a figure of 160,000 lbf [710 kN] in compound mode and seems to indicate that it was the largest TE for any locomotive up to the time [1914–1916].) 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. In total, only four Triplexes came into existence and only in the United States; all of the Erie triplexes were retired by 1930; none were preserved. The Virginian XA #700 2-8-8-8-4 was unsuccessful. It was returned to Baldwin where it was rebuilt into a 2-8-2, numbered 410, and a 2-8-8-0, numbered 610. A two wheel trailing truck was added later, making it into a 2-8-8-2. These two locomotives were operated until 1953.[ citation needed ]

Expanding the concept


In June 1914, George R. Henderson was granted US Patent 1,100,563 for a quadruplex 2-8-8-8-8-2 locomotive, [5] which was assigned to the Baldwin Locomotive Company. Baldwin submitted the design to the Atchison, Topeka, and Santa Fe Railway, which in the 1910s was a strong proponent of compound locomotives. [6] [7] [8]

This would have been, in 1913, by far the largest steam locomotive ever proposed. In quadruplex form, it would have been 129 feet 10+12 inches (39.586 m) in overall length, total weight of about 885,000 pounds (401 t), with tractive effort of 200,000 pounds-force (890 kN). [9]

Baldwin quad patent dwg.gif
Patent application drawing for the Baldwin quadruplex locomotive, 1913

The Quadruplex was to comprise three articulated engines of 8 driving wheels each beneath the locomotive itself, and a fourth engine beneath the tender. As a compound locomotive, engine cylinders 7 and 9 (as numbered on the above image) would receive high pressure steam to drive the first and third engines, each would exhaust as low-pressure steam to power cylinders 8 and 10 on the second and fourth engines. Both sets of low-pressure cylinders would then exhaust direct to atmosphere through stacks 33 and 38. Due mostly to its extreme length the design included a number of mostly untried innovations:

By the time the patent was granted, the experience of the existing triplexes and jointed boiler locomotives had shown the shortcomings of these designs, and the quadruplex did not proceed to construction.


A quintuplex version (2-8-8-8-8-8-2) was included in the patent application. The design was based on the quadruplex, with the fourth and fifth engines under an extended, articulated tender. [7] [8] [10]

An even larger 2-10-10-10-10-10-2 variant appeared as an artist’s impression in the August 1951 issue of Trains magazine. However, this idea appears to be speculative on the part of the magazine author and the artist, perhaps because AT&SF already had a fleet of 2-10-10-2’s in 1913. There is no evidence that George Henderson, nor Baldwin, proposed such a version.

Related Research Articles

Steam locomotive Railway locomotive that produces its pulling power through a steam engine

A steam locomotive is a rail vehicle that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material to heat water in the locomotive's boiler to the point when it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels.

Mallet locomotive Articulated locomotive with compound steam power

The Mallet locomotive is a type of articulated steam railway locomotive, invented by the Swiss engineer Anatole Mallet (1837–1919).

Pennsylvania Railroad class M1

The M1 was a class of steam locomotive of the Pennsylvania Railroad (PRR). It was a class of heavy mixed-traffic locomotives of the 4-8-2 "Mountain" arrangement, which uses four pairs of driving wheels with a four-wheel guiding truck in front for stability at speed and a two-wheel trailing truck to support the large firebox needed for sustained power. Although built for both passenger and freight work, they spent most of their service lives hauling heavy high-speed freight trains. Many PRR men counted the M1 class locomotives as the best steam locomotives the railroad ever owned.

4-8-8-2 Articulated locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, a 4-8-8-2 is a locomotive with four leading wheels, two sets of eight driving wheels, and a two-wheel trailing truck.

Under the Whyte notation for the classification of steam locomotives, a 2-8-8-8-4 has two leading wheels, three sets of eight driving wheels, and four trailing wheels.

Steam turbine locomotive

A steam turbine locomotive is a steam locomotive which transmits steam power to the wheels via a steam turbine. Numerous attempts at this type of locomotive were made, mostly without success. In the 1930s this type of locomotive was seen as a way both to revitalize steam power and challenge the diesel locomotives then being introduced.

LNER Class W1 Experimental steam locomotive with Yarrow boiler

The LNER W1 No. 10000 was an experimental steam locomotive fitted with a high pressure water-tube boiler. Nigel Gresley was impressed by the results of using high-pressure steam in marine applications and so in 1924 he approached Harold Yarrow of shipyard & boilermakers Yarrow & Company of Glasgow to design a suitable boiler for a railway locomotive, based on Yarrow's design.

Long Boiler locomotive

The Long Boiler locomotive was the object of a patent by Robert Stephenson and the name became synonymous with the pattern. Its defining feature is that the firebox is placed behind the rearmost driving axle. This gives a long boiler barrel, with long fire-tubes. There is thus a generous heating surface area, giving a boiler that is both powerful and efficient.

The Victorian Railways V Class is a steam locomotive, used on the Victorian Railways in the period 1900-1930.

South African Class KM 0-6-0+0-6-0

The South African Railways Class KM 0-6-0+0-6-0 of 1904 was an articulated steam locomotive from the pre-Union era in Transvaal Colony.

South African Class Experimental 2 2-8-0

The South African Railways Class Experimental 2 2-8-0 of 1902 was a steam locomotive from the pre-Union era in the Cape of Good Hope.

South African Class MA 2-6-6-0

The South African Railways Class MA 2-6-6-0 of 1909 was a steam locomotive from the pre-Union era in the Natal Colony.

South African Class MB 2-6-6-0

The South African Railways Class MB 2-6-6-0 of 1910 was a steam locomotive from the pre-Union era in the Colony of Natal.

The South African Railways Class MC 2-6-6-0 of 1912 was a steam locomotive.

South African Class MD 2-6-6-2

The South African Railways Class MD 2-6-6-2 of 1910 was a steam locomotive from the pre-Union era in Transvaal.

The South African Railways Class ME 2-6-6-2 of 1912 was a steam locomotive.

The South African Railways Class MG 2-6-6-2 of 1911 was a steam locomotive from the pre-Union era in Transvaal.

South West African 2-8-0T

The South West African 2-8-0T of 1907 was a steam locomotive from the German South West Africa era.

CGR Kitson-Meyer 0-6-0+0-6-0

The Cape Government Railways Kitson-Meyer 0-6-0+0-6-0 of 1903 was a South African steam locomotive from the pre-Union era in the Cape of Good Hope.

Jointed Boiler Locomotive

The jointed-boiler steam locomotive was a variant of the Mallet articulated locomotive, in which a flexible coupling was introduced midway along the length of the boiler casing, which allowed the boiler to bend laterally when the locomotive was on curved track.


  1. 1 2 Westing (1966), pp. 124–125.
  2. "A titan of the rails". The Independent. July 27, 1914. Retrieved July 24, 2012.
  3. 1 2 3 4 5 Westing 1966 , pp. 124–125.
  4. Leslie Paxton and David Bourne, Locomotive of the South African Railways, Struik, 1985, pp. 8–9.
  5. USpatent 1100563,Henderson, George,"Locomotive",issued 1914-06-16, assigned to Baldwin Locomotive Works
  6. "The Quadraplexes". Retrieved 28 October 2018.
  7. 1 2 Solomon, Brian, 2015. The Majesty of Big Steam. Voyageur Press. ISBN   978-0760348925
  8. 1 2 Drury, George H. (1993). Guide to North American Steam Locomotives. Waukesha, Wisconsin: Kalmbach Publishing Company.
  9. ”What Might Have Been”, Trains magazine, August 1951
  10. Trains. Kalmbach Publishing Company. 1950.