Abstract: The invention is directed to a hydraulically actuated feed and proportioning pump with a centrally located movable diaphragm which divides a main pump housing into two variable volume main fluid chambers. Each main fluid chamber has its own integral inlet and outlet valve means which enables the chambers to cyclically discharge fluid mixture which is part additive and part water obtained from a main feed line. The movable diaphragm is alternately exposed to a fluid source under pressure on one side and to a relative vacuum, created by the evacuation of fluid, on the other side.A piston is connected to the movable diaphragm and moves slidably within a piston housing forming thereby two piston chambers. The movement of the piston within its housing creates a vacuum in one of the piston chambers, and the additive (e.g.