Duplex Drive Locomotives

The first duplex drive locomotive was built in 1937 by the B&O railroad. It employed a number of features proposed by B&O's chief of motive power, George Emerson. This locomotive had a watertube firebox, a rigid frame, an air reservoir between the two front cylinders and duplex drive with the rear cylinders facing backwards. It was numbered 5600 and named "George H. Emerson". It spent a lot of time in the shops but lasted until 1950.

Of all the U.S. railroads, the Pennsylvania ("The Standard Railroad of the United States") probably experimented the most with steam locomotive designs. Most of these experiments involved duplex-drive technology.

PRR S-1 (6-4-4-6) 6100

In 1939 the PRR built their first duplex-drive locomotive. The shrouding was designed by Raymond Loewy . During the first two summers of its existence (1939-40), 6100 was displayed under steam at the New York Worlds Fair. Its drivers were supported by rollers which allowed the drivers to turn (under steam) so that the fair goers could watch. During this period, the tender was lettered "AMERICAN RAILROADS".
Was it successful?
While being an impressive puller (it could haul a 1200 ton train at 100 mph), the 6100 turned out to be too long for most of the PRR trackage and turntables. It ended up in service only between Chicago and Crestline, OH. Even so, the 6100 proved to be both a public relations success (the 6100 was featured in several calendars and very well publicized) as well as a great learning tool for the T-1s that would be designed later. 6100 was taken out of service in 1944 (after only four years of service) and scrapped in 1949.

To really appreciate how long this locomotive was, you must first have a frame of reference. Consider the Big Boy. The Big Boy was generally considered to be the "largest" steam locomotive ever. It was over 132 feet long. Unlike the Big Boy, the S-1 was not an articulated locomotive, yet, it was a whopping 140 feet long! I don't know what its designers were thinking, but the length of this locomotive was partly to blame for its failure.

PRR T-1 (4-4-4-4) 6110, 6111

Baldwin had been toying with the idea of a duplex-drive steam locomotive for some time. They were even considering building a demonstrator model. However, before they could, the PRR placed an order for two of them for delivery in 1942. These locomotive were built to lead the Fleet of Modernism -- The Broadway Limited, The General, The Admiral, The Manhattan Limited and the Pittsburgher . The locomotives were designed by Baldwin while the exterior was designed by Raymond Loewy .
Were they successful?
Yes. These two T-1s outperformed a four-unit, 5400 HP diesel consist at all speeds over 26 mph. Each of these T-1s could pull a 16 car passenger train at 100 mph. The main reason why these two T-1s were considered to be a success was because they provided no reason to curtail PRR's experimentation with duplex drive steam locomotives. The T-1s became the "4-8-4s" of the PRR. The primary advantages in a duplex-drive locomotive were considered to be:
  • Lighter machinery (total weight of reciprocating parts was less than that of a 4-8-4)
  • Shorter piston stroke
  • Smaller moving parts
  • Lower piston thrust required (because two sets of cylinders were used)
  • Smaller cylinders required resulting in higher efficiency at high speed

PRR Q-1 (4-6-4-4) 6130

In 1942 the duplex-drive 6130 was built for fast freight service on the PRR. The rear set of cylinders faced backwards. The rear cylinders were also smaller than the front cylinders as they only had to power two axles instead of three.
Was it successful?
As it turned out, the rear set of cylinders caused problems. They were in a dirty location (next to the ash pan) and because of their location, they limited the size of the firebox. Wheel slip was also a problem with this locomotive.

PRR Q-2 (4-4-6-4) 6131, 6175-6199

In 1944 the 6131 was built. A re-arrangement of the drivers and cylinders had solved the problems of the Q-1. In 1945, 25 more Q-2s were built (6175-6199). The Q-2s were the most powerful (in both HP and tractive effort) of all non-articulating steam locomotives.
Were they successful?
Yes! They were the most successful of all duplex-drive locomotives. However, because of dieselization, most had a short life and were stored by 1949. The Q-2s represented the ultimate in steam freight development in America. In a way, they could be considered the 4-10-4s of America that were never built. Sadly, none were saved.

PRR T-1 (4-4-4-4) 5500-5549

In 1945-46, two groups of T-1s were built. 5500-24 were built by the PRR in Altoona in 1945. 5525-49 were built by Baldwin in 1946. The appearance of these T-1s differed from that of the first two (6110 and 6111). The first two T-1s had sharp noses. These were more rounded. They were all painted Brunswick green. However, it was often hard to tell. Surprisingly, the shrouding made them dirty locomotives (smoke stayed close to the locomotive). Most of the T-1s were retired by 1949. Sadly, all were scrapped by 1956.
Were they successful?
The answer to this question depends on who you ask. Based on the success of the Q2 (not the original two T-1s), the PRR ordered 25 more 4-4-4-4s from Baldwin and built 25 4-4-4-4s in their own shops. The PRR insisted on using poppet valves (instead of Walschaerts valve gear) on the T-1s. Maintenance on poppet valves turned out to be high. According to most books on the subject, the T-1s turned out to be slippery locomotives even at speed. Why wasn't this known after testing the 6110 and 6111? The 6110 and 6111 were tested under ideal adhesive conditions. The later batch of T-1s ran on a larger portion of the PRR system and under all conditions. Even though the factor of adhesion was designed to be greater than 4.0, the slipping problem was never solved. At least that is what "the books" claim... It should be noted that the retired enginemen who actually ran the T1s claim that they were not unduly slippery (even at speed), as most authors have claimed. Their secret to starting trains was to put down a little sand when stopping, a little when starting, and to use a light throttle up to 25 mph. Their secret to avoiding high-speed slipping was a longer cutoff coupled with partial throttle. The T-1s ran very well at speeds over 100 MPH.

One of the main reasons why the T-1s would not be considered successful was because they required more maintenance and shop work then the E-7 diesels that were available at the time. But then, this was true of any steam locomotive and is the main reason why diesel locomotives eventually replaced steam power on all railroads. This batch of T-1s had a very short life on the PRR.

PRR T-1 (4-4-4-4) 5550

In early 2014 it has been proposed that a new T-1 4-4-4-4 duplex drive steam locomotive would be built. It is proposed that this locomotive would be used for mainline excursion service and to set the world speed record for a steam locomotive.

More Information


USA and Canadian Railroads that used Duplex Drive Locomotives

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