Duplex locomotive

Last updated November 28, 2024

A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive. The concept was first used in France in 1863, but was particularly developed in the early 1930s by the Baldwin Locomotive Works, the largest commercial builder of steam locomotives in North America, under the supervision of its then chief engineer, Ralph P. Johnson.

Technical concept

The main disadvantage of the two-cylinder locomotives is the heavy hammer blow on the rails caused by the attempt to balance the reciprocating parts with additional masses mounted in the wheels. This effect can be reduced by using multiple cylinders acting on more drive wheels.^[1]

In Europe this problem was often overcome by dividing the drive between inside and outside cylinders, or else by using articulated locomotives, although at the time it was not believed possible to run one stably at greater than 50 mph (80 km/h). American railroads generally proved to be unwilling to use locomotives with inside cylinders, so the problem of balance could not be solved by adding more cylinders per coupled wheel set. As locomotives got larger and more powerful, their reciprocating machinery had to get stronger and thus heavier, and thus the problems posed by imbalance and hammer blow became more severe. Speed also played a factor, since the forces became greater and more destructive at higher wheel speeds. Ralph P. Johnson thought that the growing size and piston thrusts of existing express passenger locomotives could not be sustained with the by-then conventional 4-8-4 two-cylinder layout. In addition, he became convinced that a single pair of cylinders with conventional valve gear and piston valves was approaching the limits in terms of steam flow.

The earliest attempt at duplex locomotive was an 0-6-6-0 tank locomotive designed by Jules Petiet in 1863 for the French Northern Railway, but the idea was not perpetuated. However, the innovation of more rigid hinges that permitted only horizontal swinging movements and not twisting or vertical movement was from ALCO, and not seen until 1936's Union Pacific Challenger ^{[ citation needed ]}.

Instead came the idea of having multiple groups of cylinders and driven wheels mounted in one rigid frame. A "duplex" version of a 4-8-4 would be a 4-4-4-4, with the eight driving wheels split into two groups of four, each with its own set of cylinders and valve gear. The reciprocating mass of both sets would be substantially less than the single set on the 4-8-4, since they would be under less stress and gentler piston thrusts. The cylinders could be smaller yet have larger, more efficient valves. The most obvious tradeoff was that, in Baldwin's proposed design, the rigid wheelbase was longer since the second set of cylinders had to be between the two sets of drivers. A solution to this was placing the second set after the second set of driven wheels facing forward, instead of ahead of them and facing rearward like the first set of cylinders. This had its own complications, and the challenges were sufficiently concerning for many roads, for whom current locomotives were taxing enough, to reject the duplex idea.

Duplex locomotives

As of 2023, none of the duplex locomotives listed below survive. Their success and whether they could have been made to work well with sufficient time and effort is still debated. A common conclusion is that the problems of the conventional steam locomotive were not as insoluble as Baldwin believed, and that the duplex arrangement created almost as many problems as it solved. However, a group of enthusiasts is in the process of building a new Pennsylvania Railroad class T1 duplex locomotive, using design improvements from the post-war steam era in the hope of achieving better performance characteristics.

Baltimore and Ohio class N-1 #5600 George H. Emerson

The first road to use the idea was the Baltimore and Ohio Railroad, which rejected a Baldwin proposal in 1932–33, but then constructed the single Baltimore and Ohio Class N-1, #5600 George H. Emerson in the railroad's own shops without Baldwin's assistance. The locomotive was completed in May 1937 and managed to retain the same coupled wheelbase as the road's current 4-8-2s by having the second set of cylinders reversed, mounted alongside the firebox, and driving the second set of coupled wheels forwards. This proved to be less than ideal, the size of the cylinders and firebox both being constrained by this location, the long steam passages proving problematic, and the cylinders suffering from the dust and heat of the nearby firebox.

The locomotive was in light service and tested until withdrawal in 1943. It was not successful enough for the B&O to express any further interest.

PRR class S1

The next usage of the duplex type was the Pennsylvania Railroad's single S1, designed to meet a requirement to operate a 1,200 short tons (1,070 long tons; 1,090 t) train at 100 mph (160 km/h) on level track and able to accelerate to that speed easily. In excess of 4,000 hp (3.0 MW) was necessary for that requirement, and to meet it Baldwin and the PRR created possibly the largest passenger steam locomotive ever built: a 6-4-4-6 locomotive 140 feet 2+1⁄2 inches (42.74 m) long and weighing 1,060,000 lb (480,000 kg) with tender. It was, in fact, too large to work over the majority of the PRR's system and was placed into service only between Chicago, Illinois and Crestline, Ohio (283 miles [455 km]). In service after December 1940, it proved powerful and capable but prone to wheelslip and surging, presaging the problems with later duplex designs. By and large, its flaws were written-off as simply the teething troubles of an early, first-cut prototype. It was taken out of service in 1946. This locomotive got the nickname "The Big Engine"

PRR class T1

The S1 did not represent Baldwin's true desires for the type, but in the design of the T1, of which two prototypes were ordered in July 1940, Baldwin was given much more freedom. The PRR's requirements were the use of the Belpaire firebox and the Franklin oscillating-cam poppet valve gear. The two, #6110 and #6111, were delivered in April and May 1942. Testing again proved them to be powerful and capable, but not sure-footed.

As soon as wartime restrictions on producing passenger locomotives were eased in February, 1945, the PRR placed an order for 50 production examples. This was a fateful step, since the problems encountered with the prototypes had not been ironed-out nor had they been tested with the intensity required to be sure of production reliability. The production locomotives differed in detail in their streamlined casings and in the suspension, in an attempt to increase adhesion.

Problems became apparent very soon. The locomotives were incredibly-susceptible to violent wheelslip, not just at starting but also at speed. Dividing the drive into two groups meant that each group was much more likely to slip. A theory has been advanced that the more rapid, "sharper" opening of the valves with the poppet valve gear exacerbated the problem. Worse, such violent high-speed slipping could damage the valve gear components. This was a major problem on a locomotive with the poppet valve gear because, unlike the familiar piston valves and outside Walschaerts valve gear of other locomotives, many of the components were nearly inaccessible within the frame. Their complexity meant that availability and reliability proved poor, and, while a very capable locomotive engineer (driver) could extract great performance from a T1, they proved rather unsuccessful in service.

Whether the problems were soluble has been contentious ever since. However, the much easier solution of the diesel locomotive was taken within months of the production locomotives being delivered, and within 2 years all principal passenger trains were diesel-hauled. The T1s spent a few more years in lesser service before being withdrawn in 1952.

A nonprofit group known as the T1 Trust is in the process of constructing a new duplex locomotive, a T1-class engine known as Pennsylvania Railroad 5550, intending to utilize design improvements from the postwar steam era not used or seldom tested on pre-existing T1s in the hope of creating better performance characteristics. The estimated year of completion for the project is 2030.^[2]

PRR Q1

The PRR also desired to apply the duplex principle to freight haulage, and the Q1 was the first experiment in that direction. It was a 4-6-4-4 fast freight locomotive, delivered in May 1942. Like the B&O's George H. Emerson it had the second pair of cylinders facing backwards, and all were fitted with standard Walschaerts valve gear. The wheels were of 77 inches (1.956 m) diameter (ill-suited for freight hauling) and the engine was streamlined more like a passenger engine. The streamlining was later removed, as it restricted maintenance work. The rear-facing cylinders were also problematic, partially due to the inconvenient placement of being directly below the engine's firebox. Furthermore, the large drivers and smaller than adequate firebox grate area may have contributed to further problems as well. The limited firebox size was also a direct effect of the backward-facing cylinders. The lone Q1, PRR 6130, was constructed at the PRR's Altoona Works in 1942 and withdrawn from service in 1946.

PRR Q2

Production locomotives followed from the end of 1944, but these were rather different, the lesson that backward-facing cylinders next to the firebox were a poor design choice made clear. The production Q2 locomotives were of 4-4-6-4 arrangement; they were the largest non-articulated locomotives ever built and the most powerful locomotives ever static-tested, producing 7,987 hp (5,956 kW) on the PRR's static-test plant. The Q2 locomotives were also the most powerful steam locomotive ever constructed with ten driving wheels.

In operation, the Q2 could outperform pre-existing freight engines hauling double the tonnage of their predecessors. Furthermore, the Q2 had no problems building up steam power and was known to be a very smooth-riding engine. 26 were built at PRR's Altoona Works, and they were by far the most successful duplex type. The duplex propensity to slip was combated by an automatic slip control mechanism that reduced power to the slipping unit. The slip control mechanism was not always responsive, and its complexity often lead to maintenance crews not maintaining it during overhauls.

Despite overall success, the Q2s were all out of service by 1951. With dieselization, they were the obvious first targets to be withdrawn since they were only a little more capable than the conventional J1 class 2-10-4s, but with far higher running costs and maintenance loads.

PLM 151 A

In France, the duplex type was made famous by the ten 2-4-6-2 compound locomotives built in 1932 for the Chemins de fer de Paris à Lyon et à la Méditerranée (PLM) to haul heavy freight trains on the 0.8% grade of the Paris–Marseille railway between Les Laumes and Dijon. The performance was so good that the company wanted to order more engines, but the nationalization of the railways in 1938 stopped all projects. These duplex engines were fitted with Lenz-Dabeg rotary cam valve gear and soon thereafter with double exhaust. The low-pressure cylinders drove the first two coupled axle, and the high pressure cylinders the second set of drive wheels consisting of three axles. Both groups of drivers where linked with inside connecting rods through inside cranks on the second and third drivers, making this locomotive a true 2-10-2. The driving wheels had a diameter of 1.50 m (4 ft 11 in). The highest permissible speed was 53 mph (85 km/h).

In a test on December 19, 1933, the engine developed slightly more than 3,000 hp (2,200 kW) at the drawbar over a distance of 37 miles (60 km) and a speed of at least 46 mph (74 km/h), without being overworked. In ordinary service these engines could haul 1,375 short tons (1,228 long tons; 1,247 t), sustaining 31 mph (50 km/h) at the summit of the 0.8% Blaisy grade. After electrification of the line, the 151A's were sent for service in northeastern France. They were withdrawn from service in 1956 and scrapped.

Related Research Articles

A steam locomotive is a locomotive 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 where it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels.

Under the Whyte notation for the classification of steam locomotives, 4-6-2 represents the wheel arrangement of four leading wheels on two axles, six powered and coupled driving wheels on three axles and two trailing wheels on one axle. The 4-6-2 locomotive became almost globally known as a Pacific type after a locomotive built by the Baldwin Locomotive Works in Philadelphia was shipped across the Pacific Ocean to New Zealand.

Under the Whyte notation for the classification of steam locomotives, 4-8-2 represents the wheel arrangement of four leading wheels, eight powered and coupled driving wheels and two trailing wheels. This type of steam locomotive is commonly known as the Mountain type, though the New York Central Railroad used the name Mohawk for their 4-8-2s.

<span class="mw-page-title-main">2-10-4</span> Locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, a 2-10-4 locomotive has two leading wheels on one axle, usually in a Bissel truck, ten coupled driving wheels on five axles, and four trailing wheels on two axles, usually in a bogie. These were referred to as the Texas type in most of the United States, the Colorado type on the Burlington Route, and the Selkirk type in Canada.

Under the Whyte notation for the classification of steam locomotives, 2-10-0 represents the wheel arrangement of two leading wheels on one axle, ten powered and coupled driving wheels on five axles, and no trailing wheels. This arrangement was often named Decapod, especially in the United States, although this name was sometimes applied to locomotives of 0-10-0 "Ten-Coupled" arrangement, particularly in the United Kingdom. Notable German locomotives of this type include the war locomotives of Class 52.

Locomotive classification on the Pennsylvania Railroad took several forms. Early on, steam locomotives were given single-letter classes. As the 26 letters were quickly assigned, that scheme was abandoned for a more complex system. This was used for all of the PRR's steam locomotives, and — with the exception of the final type bought — all electric locomotives also used this scheme.

The Pennsylvania Railroad K4 was a class of 425 4-6-2 steam locomotives built between 1914 and 1928 for the PRR, where they served as the primary main line passenger steam locomotives on the entire PRR system until late 1957.

The Pennsylvania Railroad (PRR) N1s was a class of 2-10-2 "Santa Fe" steam locomotives built for the Pennsylvania's Lines West. 60 engines were built between December 1918 and November 1919, and worked heavy mineral freight to and from ports on the Great Lakes until their retirement in the late 1940s. All examples were scrapped by 1950.

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.

The Pennsylvania Railroad (PRR) class T1 duplex-drive 4-4-4-4 steam locomotives, introduced in 1942 with two prototypes and later in 1945-1946 with 50 production examples, were the last steam locomotives built for the PRR and arguably its most controversial. They were ambitious, technologically sophisticated, powerful, fast and distinctively streamlined by Raymond Loewy. However, they were also prone to wheelslip both when starting and at speed, in addition to being complicated to maintain and expensive to run. The PRR decided in 1948 to place diesel locomotives on all express passenger trains, leaving unanswered questions as to whether the T1's flaws were solvable, especially taking into account that the two prototypes did not have the problems inherent to the production units.

A 4-4-4-4 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has a four-wheel leading truck, two sets of four driving wheels, and a four-wheel trailing truck. While it would be possible to make an articulated locomotive of this arrangement, the only 4-4-4-4s ever built were duplex locomotives—with two sets of cylinders driving two sets of driven wheels in one rigid frame, essentially a 4-8-4 with divided drive.

The Pennsylvania Railroad's S2 class was a steam turbine locomotive designed and built in a collaborative effort by Baldwin Locomotive Works and Westinghouse Electric & Manufacturing Company, as an attempt to prolong the dominance of the steam locomotive by adapting technology that had been widely accepted in the marine industry. One was built, #6200, delivered in September 1944. The S2 was the sole example of the 6-8-6 wheel arrangement in the Whyte notation, with a six-wheel leading truck keeping the locomotive stable at speed, eight powered and coupled driving wheels, and a six-wheel trailing truck supporting the large firebox. The S2 used a direct-drive steam turbine provided by the Westinghouse Electric & Manufacturing Company, geared to the center pair of axles with the outer two axles connected by side rods; the fixed gear ratio was 18.5:1. Such design was to prevent energy loss and S2 achieved a mechanical efficiency of 97% which means only 3% of steam energy was lost within the propulsion equipment. The disadvantage of a direct-drive steam turbine was that the turbine could not operate at optimal speeds over the locomotive's entire speed range. The S2 was the largest, heaviest and fastest direct-drive turbine locomotive design ever built.

The Pennsylvania Railroad's class K5 were experimental 4-6-2 "Pacific" types, built in 1929 to see if a larger Pacific than the standard K4s was worthwhile. Two prototypes were built, #5698 at the PRR's own Altoona Works, and #5699 by the Baldwin Locomotive Works. Although classified identically, the two locomotives differed in many aspects, as detailed below. They were both fitted with a much wider boiler than the K4s, but dimensionally similar to those of the I1s 2-10-0 "Decapods". Most other dimensions were enlarged over the K4s as well; the exceptions being the 70 square feet (6.5 m²) grate area and the 80 in (2.032 m) drivers.

The PRR S1 class steam locomotive was a single experimental duplex locomotive of the Pennsylvania Railroad. It was designed to demonstrate the advantages of duplex drives espoused by Baldwin Chief Engineer Ralph P. Johnson. The S1 class was the largest rigid frame passenger steam locomotive ever built. The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy.

The Pennsylvania Railroad class Q1, #6130, was a single experimental steam locomotive designed for dual service. The locomotive entered service in 1942, and retired in 1949 after accumulating a relatively low 165,000 service miles.

<span class="mw-page-title-main">Pennsylvania Railroad Q2 class</span>

The Pennsylvania Railroad's class Q2 comprised one prototype and twenty-five production duplex steam locomotives of 4-4-6-4 wheel arrangement built between 1944 and 1945.

The PRR J1 was a class of 2-10-4 "Texas" type steam locomotives built between 1942 and 1944. The J1 had over 95,000 pounds-force (422.6 kN) of tractive effort, plus an additional 15,000 lbf (66.7 kN) if the booster engine was used.

The South African Railways Class 19C 4-8-2 of 1935 was a steam 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 spacing of the driving wheels to accommodate a larger firebox.

Pennsylvania Railroad 5550 is a mainline duplex drive steam locomotive under construction in the United States. With an estimated completion by 2030, the locomotive will become the 53rd example of the Pennsylvania Railroad's T1 steam locomotive class and the only operational locomotive of its type, as well as the largest steam locomotive built in the United States since 1952. The estimated cost of PRR 5550 was originally $10 million, but an updated projected cost of $7 million was released with the acquisition of an existing long-haul tender from the Western New York Railway Historical Society in August 2017. Construction began in 2014 with the casting of the locomotive's keystone-shaped number plate. As of February 2024 the locomotive was 43% complete.

References

↑ Holcroft, H. (1909-03-16). "Arrangement of locomotive cylinders" (PDF). Trans. Swindon Engineering Soc. (92). Swindon: GWR Mechanics' Institution: 99.
↑ "FAQ Section - The T1 Trust". The Pennsylvania Railroad T1 Steam Locomotive Trust. 2016. Archived from the original on 2019-08-24. Retrieved 2017-04-22.

Sources

Cravero, Carlo (2011). "Le locomotive a vapore americane tipo Duplex=American steam locomotives: the Duplex". Ingegneria ferroviaria (in Italian and English). 66 (5): 413–447.
Reed, Brian (June 1972). Loco Profile 24: Pennsylvania Duplexii. Profile Publications.
Staufer, Alvin (1962). Pennsy Power. Staufer. LOC 62-20872.
Vilain, L.M. (1971). L'évolution du matériel moteur et roulant de la Cie. PLM. Vincent, Fréal et Cie Paris.

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[1] Holcroft, H. (1909-03-16). "Arrangement of locomotive cylinders" (PDF). Trans. Swindon Engineering Soc. (92). Swindon: GWR Mechanics' Institution: 99.

[T1Trust01-2] "FAQ Section - The T1 Trust". The Pennsylvania Railroad T1 Steam Locomotive Trust. 2016. Archived from the original on 2019-08-24. Retrieved 2017-04-22.

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v t e Steam locomotive wheel arrangements (Whyte notation)
Single engine types	0-2-2 0-2-4 2-2-0 2-2-2 2-2-4T 4-2-0 4-2-2 4-2-4T 6-2-0 0-3-0 (monorail) 0-4-0 0-4-0+4 0-4-2 0-4-4T 0-4-6T 2-4-0 2-4-2 2-4-4T 2-4-6T 4-4-0 4-4-2 4-4-4 4-4-6 0-6-0 0-6-2 0-6-4T 0-6-6T 2-6-0 2-6-2 2-6-4 2-6-6T 4-6-0 4-6-2 4-6-4 0-8-0 0-8-2 0-8-4T 0-8-6 2-8-0 2-8-2 2-8-4 2-8-6 4-8-0 4-8-2 4-8-4 4-8-6 6-8-6 0-10-0 0-10-2 2-10-0 2-10-2 2-10-4 4-10-0 4-10-2 0-12-0 2-12-0 2-12-2 2-12-4 4-12-2 4-14-4
Divided drive and Duplex engine types	0-2-2-0 2-2-2-0 2-2-2-2 2-2-4-0T 4-2-2-0 2-4-6-2 4-4-4-4 6-4-4-6 4-4-6-4 4-6-4-4
Articulated locomotives Fairlie, Meyer and Garratt types	0-4-0+0-4-0 2-4-0+0-4-2 2-4-2+2-4-2 4-4-2+2-4-4 0-6-0+0-6-0 0-6-2+2-6-0 2-6-0+0-6-2 2-6-2+2-6-2 4-6-0+0-6-4 4-6-2+2-6-4 4-6-4+4-6-4 2-8-0+0-8-2 2-8-2+2-8-2 4-8-0+0-8-4 4-8-2+2-8-4 4-8-4+4-8-4
Articulated locomotives Mallet types	0-4-4-0 0-4-4-2 2-4-4-0 2-4-4-2 0-6-6-0 2-6-6-0 2-6-6-2 2-6-6-4 2-6-6-6 2-6-8-0 4-4-6-2 4-6-6-2 4-6-6-4 0-8-6-0 0-8-8-0 2-8-8-0 2-8-8-2 2-8-8-4 4-8-8-2 4-8-8-4 2-10-10-2
Articulated locomotives Triplex and other Multiplex types	2-8-8-8-2 2-8-8-8-4 2-8-8-8-8-2 0-6-2+2-4-2-4-2+2-6-0 2-6-6-2+2-6-6-2 2-8-8-8-8-8-2 2-10-10-10-10-10-2 2-4-4-2+2-8-8-2+2-4-4-2
Articulated locomotives Engerth types	0-4-4 0-4-6 2-6-4 0-6-4 0-6-4-0 0-8-4 0-8-6
Geared locomotives	Shay Climax Heisler Willamette
Other notation forms: AAR Swiss UIC