The Humphrey Pump H A Humphrey MIMechE A four-stroke engine with no pistons or crankshaft, Humphrey's ingenious invention patented in 1906 acts directly upon the water it pumps. This gas fuelled example, built by William Beardmore & Co., served Cobdogla from 1927 to 1965. Restored in 1985, it is the only working Humphrey Pump in the world.