Abstract: The present invention relates to a hydraulically controlled diaphragm pump, comprising an intermediate chamber filled with fluid, and a re-filling conduit for said chamber.According to the invention, means are provided for controlling the closing and the opening of the said conduit, which means are constituted by a valve cooperating with a fixed seat through which the said re-filling conduit reaches into the said intermediate chamber. Said valve is mounted for sliding on a rod, which rod is also mounted for sliding longitudinally inside a fixed support in the said intermediate chamber and traverses the said seat, a shoulder of the said rod forming means for moving the said valve and holding it on its seat, an actuating surface of the said rod, opposite the said shoulder, forming the rear of the diaphragm and a spring being coupled between the said support and the said actuating surface for closing the said valve.The invention finds an application in the field of mechanical engineering.