Abstract: A variable liquid discharge flow rate pump with a discharge float valve the opening of which is controlled according to the discharge pressure and flow rate by a hydraulic power ram actuator with a resiliently biased piston slidable in a cylinder communicating with or forming a container space for transit of liquid from a first cavity in which prevails the discharge pressure to a second cavity in which prevails the inlet pressure, the hydraulic circuit comprising at least one passageway providing a head loss variable according to the discharge flow rate and pressure.