Duplex Locomotive - PRR Class T1

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 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. What is undeniable is that the PRR very soon did not care; 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 The T1s spent a few more years in lesser service before being withdrawn in the early 1950s.