Willans steam engine. Diagram of a cross-section through a Willans two-crank steam engine. Developed by the British engineer P. W. Willans in the late nineteenth and early twentieth century, this central-valve steam engine was a high-speed design used in early electrical power stations. In 1895, around half of the UK's electrical supplies were provided by Willans engines. The diagram shows the flywheel (lower left), the main piston (right) and a valve spindle (left). The piston and spindle dipped into the oil reservoir at bottom to obtain lubrication while running. Steam entered from top right to drive the whole process.