Abstract: The invention relates to an improvement in variable capacity diaphragm pumps. According to the invention, the piston is driven by a cam fast with the wheel of a speed reducing gear pair, the eccentric/wheel assembly rotating idly on a fixzed shaft of which the axis is perpendicular to the axis of the piston, the piston terminating in a U-shaped shank of which the wings are perpendicular to the axis of the piston and spaced apart by a length slightly greater than the diameter of the eccentric, and of which the base is perpendicular to said fixed shaft and is provided with a longitudinal groove parallel to the axis of the piston which is traversed by the fixed shaft, the eccentric being housed between the wings of the shank. The invention is more particularly applicable to the manufacture of diaphagm pumps.

Abstract: A pump in accordance with the invention has moving equipment (32) driven by a reversible synchronous motor (42) whose windings (44, 45) are connected to a power source by means of optocoupled triacs (48, 49) which, under microprocessor control, are used to adjust the flow rate of the pump by acting on its admission period (by powering the windings in one direction) and on the pumping cycle time (by varying the period for which the pump is unpowered in each cycle).