Worthington duplex pumping engine, 1891. A duplex steam pump has two sets of steam and water cylinders. They are not physically connected but the steam valves on the first pump are operated by the movement of the second pump's piston rod, and vice-versa. The result is that there are no "dead spots" and the pump is always self-starting. Henry Rossiter Worthington (December 17, 1817 - December 17, 1880) was an American mechanical engineer. He had several inventions leading to the perfection of the direct steam pump (1845-55), patented the duplex steam pump (1859), and built the first duplex waterworks engine, widely adopted and used for more than 75 years. He established a pump manufacturing plant, New York City, in 1859. He was a key founder of the American Society of Mechanical Engineers in 1880.