The pump is the most widely used turbomachine and is the subject of intensive research and development. It is believed to be the second most frequently built machine of modern times, next to the electric motor. Pumps reach efficiency levels above 90% and are built with powers ranging from a few watts to megawatts. As pumps have evolved to handle a wider range of liquids at higher pressures and temperatures, whole industries have become dependent on them. The complex flow in pumps makes them among the most complicated fluid machines ever built. Although the most rapid development of pumps has occurred since around 1940, the pump has a long history that parallels the rise of modern engineering itself.