Abstract: A fluid driven reciprocating pump is described, particularly for use in feeding fertilizer solution to an irrigating water line, the pump being driven solely by the pressurized water in the supply line and requiring no electricity or other power source for either driving or controlling the pump. The described pump includes a pair of flexible diaphragms defining a pair of expansible chambers, and a reciprocating rod connecting the diaphragms to each other so that they move in unison. A main valve supplies pressurized water to the expansible chambers, and a pilot valve controlled by operator elements carried by the reciprocating rod controls the main valve connections to the pair of expansible chambers such as to effect an expansion and contraction of the chambers.