At the heart of a Class 50 is a EE16CSVT power unit built by English Electric. This is a development of the unit found in Class 40 diesels which in turn can trace its origins back to those that powered the two pioneer London, Midland and Scottish Railway (LMS) diesel-electric locomotives back in 1947.

The unit is a medium-speed, 16-cylinder four-stroke, direct injection engine developing 2,700bhp at its maximum speed of 850rpm. The cylinders have a 10 inch diameter and a 12 inch stroke. They are arranged in a V-formation, with the twin banks of cylinders driving a common crankshaft. For each set of four cylinders there is a separate turbocharger and charge cooler.

At the heart of a Class 55 (Deltic) are two Napier Deltic D18-25B power units, developed by the Napier company of Liverpool as a compact high-power unit for propelling fast patrol boats. It was named after its unusual shape, an inverted triangle similar to the greek letter Delta.

Each unit is a high-speed, 18-cylinder two-stroke engine developing 1,650bhp at their maximum speed of 1,500rpm. An engine has three banks of six cylinders arranged in a triangle with three crankshafts. Two opposed pistons are fitted in each cylinder which are then attached to the crankshafts, one at each apex. The crankshafts are connected via a series of phasing gears to drive one output shaft to the main generator.

Photographs of Class 50 power unit number IH6937, now fitted to 50026 Indomitable, appear courtesy of Darryl Tebbs.

Dates: 2007-2012

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EE16CSVT, "Class 50"

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EE16CSVT, "Class 50"

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EE16CSVT, "Class 50"

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EE16CSVT, "Class 50"

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D18-25B, "Class 55", Deltic

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D18-25B, "Class 55", Deltic