In 1884 and 1885 Peter Willen (1851-1892) patented his central valve engine. In this design the steam was distributed by a piston valve inside a hollow piston rod, worked by an eccentric on the crankpin. The engine was vertical, totally enclosed splash lubricated. It was made with tandem cylinders as simple, compound or triple expansion and with one, two, or three cranks. It was manufactured to close limits so that the parts were interchangeable. It was ultimately built in sizes up to 2,500 horse power and was very economical.
The Willens engine held its own for twenty years, when it was finally rendered obsolete by the steam turbine about 1904.