A T1 at the Baldwin plant ready for delivery to the PRR
The Pennsylvania Railroad's 52 T1 class duplex-drive 4-4-4-4 steam locomotives, introduced in 1942 (2 prototypes) and 1945-1946 (50 production), were their last steam locomotives built and their most controversial. They were ambitious, technologically sophisticated, powerful, fast, and distinctively streamlined by Raymond Loewy. However, they were also prone to violent wheelslip both when starting and at speed, complicated to maintain, and expensive to run. The PRR vowed in 1948 to place diesel locomotives on all express passenger trains, leaving unanswered the question of whether the T1's flaws were solvable. An article in the Pennsylvania Railroad Technical and Historical Society Magazine published in 2008 revealed that the wheel-slip problems may have been caused by the failure to properly train engineers transitioning to the T1, resulting in excessive throttle applications, which in turn caused the driving wheels to slip. Another root cause of wheel slip was faulty spring equalization. The drivers were equalized together and not equalized with the engine truck. In the field, the PRR equalized the engine truck with the front engine and the trailing truck with the rear engine.
Before the T1, the last production express passenger engine the PRR had produced was the K4s of 1914, produced until 1928. Two experimental enlarged K5 locomotives were produced in 1929, but they were not considered enough of an improvement to be worthwhile. After that the PRR's attention switched to electrification and the production of electric locomotives; apparently the railroad had no need for more steam locomotives.
But the deficiencies of the K4s became more obvious during the 1930s. They were fine locomotives, but as train lengths increased they proved too small; double headed K4s locomotives became the norm on many trains. The railroad had locomotives to spare, but paying two crews on two locomotives per train was expensive. Meanwhile, other railroads were leaping ahead, developing larger passenger power. Rival New York Central built 4-6-4 Hudsons, while other roads developed passenger 4-8-2 "Mountain" types and then 4-8-4 "Northern" designs. The PRR's steam power began to look outdated.
The PRR began to develop steam locomotives again in the mid-to-late 1930s, but with a difference. Where previous PRR locomotive policy had been conservative, new radical designs took hold. Designers from the Baldwin Locomotive Works, the PRR's longtime development partner, persuaded the railroad to adopt Baldwin's latest idea: the duplex locomotive. This split the locomotive's driving wheels into two sets, each with its own pair of cylinders and rods. Previously, the only locomotives with two sets of drivers were articulated locomotives, but the duplex used one rigid frame. In a duplex design, cylinders could be smaller and the weight of side and main rods could be drastically reduced. Given that the movement of the main rod could not be fully balanced, the duplex design would reduce "hammer blow" on the track. The lower reciprocating mass meant that higher speeds could be achieved. Use of poppet valves also increased the speed because they gave very accurately-timed steam delivery to the cylinders. However, there was a drawback of the metallurgy used; the poppet valve could not take the stress of sustained high speed operation (meaning over 100 mph (160 km/h) on production T1s).
The first PRR duplex was the single experimental S1 of 1939. This proved successful, but it was too large, and its turning radius prohibited it from operating over most of the PRR's network. The PRR returned to Baldwin to develop a duplex design fit for series production. The two Baldwin prototypes (#6110 and #6111) delivered glowing test reports, resulting in a production order for 50 T1s, split between the PRR's own Altoona Works and Baldwin. The last production T1 (#5549) entered service on August 27, 1946. The machines used the PRR 3 chime standard whistle used in the passenger locomotives.
Engine #5539 developed 5,012 hp (3,737 kW), as tested between September 11, 1946 and September 14, 1946 by Chesapeake and Ohio Railway dynamometer car DM-1 while on loan to C&O. In 1944 #6110, tested in Altoona, developed 6,550 hp (4,880 kW) in the cylinders at 85 mph (137 km/h).
Due to their complexity relative to other steam locomotive designs, T1s were known to be difficult to maintain. Recommended to a maximum speed of 100 miles per hour (161 km/h), T1s were so powerful that they could easily exceed their designed load and speed limitations, which in turn often caused wear and tear issues. A technician charged with determining the cause of frequent poppet valve failures on the T1s claimed to have observed them being operated at speeds of up to 140 mph (225 km/h) to make up time. The T1 was designed to run reliably at speeds of up to 100 mph (160 km/h). Although such reports are viewed as dubious, some think T1s regularly exceeded 100 mph (161 km/h), making them among the fastest steam locomotives ever built. The price paid for such speed was higher maintenance costs and increased failures in service.
The T-1 4-4-4-4 had such power that the engineer, if not careful on the throttle, could have violent wheel slip at 100 miles per hour, causing damage to the poppet valves. They were described as "free steaming", meaning they could maintain boiler pressure regardless of throttle setting.
Most T1s, having been displaced by new diesels, were out of service by 1952. All T1 locomotives were sold for scrap between 1951 and late 1955. The last engines were towed westward for scrapping in early 1956. However, an exact scale live steam replica in 1 inch/foot scale (1:12) has been built by Ed Woodings, using the original T1 plans. In addition, the T1 has proven a fairly popular subject to be reproduced in model form.
A non-profit group known as the T1 Locomotive Trust plans to build an all-new, fully operational T1 using the original plans but incorporating design and performance improvements where necessary. Their main goal is to have it beat the world speed record held by the LNER Class A4 4468 Mallard at 126 mph. The alleged speeds of over 140–150 miles an hour give them hope of beating it. They estimate the cost to be $10 to $20 million and that it would take up to 20 years to see completed. In late 2015 the project had fabricated driver casting forms but no major building had yet commenced.
- South Australian Railways 520 class the Australian locomotive with similar streamlining style.
- Staufer, Alvin (1962). Pennsy Power. Staufer. pp. 216–225. LOC 62-20872.
- Brian Reed (June 1972). Loco Profile 24: Pennsylvania Duplexii. Profile Publications.
- Reed 1972, p. 271.
- Reed 1972, p. 275.
- "In Defense of the 5500's", Volume 41, Number 1, Pennsylvania Railroad Technical and Historical Society Magazine, Spring, 2008
- "Pennsy T1 comeback? Ten questions and answers for the T1 Trust", Volume 75, Number 5, Trains Magazine, May 2015.
- Rivanna Chapter, National Railway Historical Society (2005). "This Month in Railroad History: August". Retrieved 2006-08-25.
- Reed 1972, p. 279.
- "The T1 Trust". T1 Trust for constructing PRR T1 5550. The T1 Trust. Retrieved 1 December 2015.
- Chesapeake & Ohio Tests the PRR T1 - Chesapeake and Ohio Historical Magazine, May 2005 by Stephenson, David R - The C&O test report contains information that is not widely known, and some of it contradicts generally accepted beliefs about the T1.
- Photos of PRR 4-4-4-4 locomotives
- An N Scale PRR T1 4-4-4-4 scratchbuilding project
- A group that intends to build a full size PRR T1
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