Abstract: A hydraulic fluid control system regulates the delivery rate of feed water to a boiler. A hydraulic actuated diaphragm pump having a plurality of diaphragm working chambers which are interconnected with check valve controlled inlets and outlets pumps the feed water to the boiler. Fluid surges or pulsations are prevented by the use of projection members on the face of the diaphragms and by a variably controlled pressure regulator responsive to the feed water pressure. The delivery rate of hydraulic fluid to the diaphragms controls the actual pumping output. A bypass line including a pressure regulating valve with pilot control and a modulating control valve controls a bypass hydraulic fluid rate which directly corresponds to the pumping output rate.