Pump Unit

a set of devices, usually consisting of a pump, a motor, and a transmission. Pump units may be stationary (mounted on foundations or in wells or other locations) or movable (mounted on a trailer or chassis). In terms of the type of motor, pump units may be of the electric, turbine, diesel, or motor (internal-combustion) types.

The first pump units, described in 1613 by G. Zeising, were driven by a water wheel. Later, T. Savery (1698) and T. Newcomen (1712) proposed pump units based on a new principle that used steam and air pressure. Since the early 20th century, electrically driven pumps have been the most common. Low-power pump units are usually of unitized construction, with some subassemblies common to the pump and the motor (for example, the direct-acting, two-cylinder piston-type steam pump patented by the American engineer Henry R. Worthington in 1849). In nonunitized pump units the pump and motor are connected by a semirigid friction coupling or by a transmission in which the ratio of the speeds of rotation of the shafts is fixed or variable. Belt drives with plain or stepped pulleys, as well as induction (electromagnetic) sliding couplings, are used. Pump units are usually component parts of pumping plants and pumping stations.