Pennsylvania No. 5550 is a 4-4-4-4 class T1 duplex locomotive currently under construction by the T1 Trust. The locomotive's completion date is currently estimated to be around 2030. The locomotive will be built to the early appearance of the production class, and will be fitted with Rotary-Cam Valve Gear.
Introduction[]
The Pennsylvania Railroad class T1 class steam locomotive was one of the most unique and controversial classes of locomotives ever constructed. This was due to its unusual Duplex drive 4-4-4-4 wheel arrangement, its use of the Franklin Type A oscillating-cam poppet valve, and its characteristic streamlining conceived by renowned industrial designer Raymond Loewy. The T1 was also the only class of Pennsylvania duplex able to travel the railroad's entire network and the first production series locomotive designed to use the poppet valve. The two prototype T1 locomotives were constructed in 1942 by the Baldwin Locomotive Works, numbered 6110 and 6111 respectively. Of the fifty production units, twenty-five (numbered 5500 to 5524) were constructed at the Pennsylvania Railroad's Altoona Works and twenty-five (numbered 5525 to 5549) at Baldwin, for a total of fifty-two T1 class locomotives. This made the T1 the most-produced of all the Pennsylvania Railroad's duplex-drive locomotives.
The T1 class suffered from several performance and design issues, including difficulties with the poppet valves. The original materials used to construct the valves were subject to fatigue issues, particularly when the locomotives were operated above 100 miles an hour. In 1947, a higher-strength and fatigue-resistant alloy was used and retrofitted to the T1 class to solve the fatigue problems. Nevertheless, the design of the Franklin Type A poppet valves made several key areas of the valves hard to access during maintenance overhauls. Despite these issues, the poppet valves did improve the T1's high-speed performance, requiring less horsepower and distributing steam flow with greater precision. The T1 locomotives were further burdened by excessive wheel slip on one of the two engine sets at startup or high speed.[1] The Pennsylvania Railroad tried to address the problem by changing the spring bed arrangement on the T1—from a single bed, supporting all eight drivers, to two beds, each of which supported one of the engines and its adjacent truck. However, no complete solution was found to the problem of wheel slip, even though an "anti-slip" mechanism had been previously installed on the PRR Q2-class duplex. One possible reason is that the engineers, familiar with the slower throttle action of the K4 class, were unprepared for the T1's more immediate throttle response.
Before many of the problems that plagued the T1 class could be solved, the Pennsylvania Railroad decided to begin the transition from steam power to diesel. Moreover, these problems ensured that the T1 class would be retired before more reliable steam engine classes such as the K4s. The T1 locomotives were retired between 1952 and 1953. Scrapping began in 1953, and the last surviving T1 was scrapped in 1956.[5] The hasty retirement of the T1 left several performance-related and technical questions unanswered.
T1 Trust[]
The Pennsylvania Railroad T1 Steam Locomotive Trust, also referred to as the T1 Trust, is a non-profit public charity founded in 2013. The T1 Trust is composed of railroading experts who intend to build the 53rd member of the T1 class and put it into mainline steam excursion service within the United States. The last production T1 bore the number 5549, making 5550 the logical choice for the new locomotive's number. The T1 Trust's goal was to construct the locomotive within 17 years (by 2030) at an estimated cost of $10 million.[11] The price is based on calculated costs for inflation, labor, material, fabrication, retooling, and design. Lessons learned during Tornado's construction in the U.K. were also taken into account. The T1 Trust chose to build a T1, rather than a proven design such as the New York Central Railroad's "J" class Hudsons, to test the T1 class's long-rumored performance and to avoid conflicts of interest with other locomotive replication projects.
World Steam Speed Record[]
The builders of PRR 5550 hope to break the world steam speed record, which is held by the LNER Class A4 4468 Mallard at 126 mph (203 km/h). The 5550 will operate under its original design with no major modifications in its attempt to break the record. It has been unofficially reported that PRR T1 locomotives were capable of achieving speeds in excess of 140 mph (230 km/h) with fully loaded trains, and the T1 Trust believes the original T1 design is capable of achieving this feat.
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