This type of piston pump, directly driven by a reciprocating steam engine, is commonly called donkey steam pump. It is constituted by a double-acting reciprocating engine which is permanently connected via a stem with the piston of a double-acting reciprocating pump, equipped with automatic valves. Through a system of connecting rods and rocker arms, the stems control the distribution sliders of the engine. The piston of the engine always has a diameter larger than that of the pump piston so as to give the liquid a pressure higher than that of the steam and then allow it to enter the steam generator. The donkey features the advantage to adjust the amount of liquid to be sent to the generator to very low values, by acting on the steam admission valve into the engine. By contrast its use requires a non negligible consumption of steam. This type of machine was commonly used in industrial, marine steam plants and in some locomotive as service or reserve units, up to the first half of the XX century.
Commonly used in industrial, marine steam plants and in some locomotive as service or reserve units, up to the first half of the XX century.
