“Donkey” steam pump

This type of piston pump, directly driven by a reciprocating steam engine, is commonly called donkey steam pump. The donkey is constituted by a double-acting reciprocating engine which is permanently connected via a rod with the piston of a double-acting reciprocating pump, equipped with automatic valves. The stem, through a system of connecting rods and rocker arms, controls the distribution slider of the engine. The piston of the engine always has a diameter larger than that of the pump piston so as to impart to the liquid a pressure higher than that of the steam and then allow it to enter the steam generator. By means of donkeys, one has the advantage, by acting on the steam admission valve into the engine, to adjust the amount of liquid to be sent to the generator to very low values . By contrast there is a non negligible consumption of steam.