The invention relates to a diaphragm failure detection device for a hydraulically driven pump. The device has a hollow body in which a chamber is formed at an end of the body and a duct connects the chamber to another end. A check valve allows a fluid to pass to the chamber. A piston is mounted to move in translation in the body. The piston has a portion co-operating in a sealed manner with the chamber, where the portion is passed through a hole of diameter greater than that of a free ball of the valve. The piston has another portion co-operating in a sealed manner with the former portion to form a closed end of the piston remote from the latter end. Independent claims are also included for the following: a method for mounting a break detecting device on a pump and a hydraulically-actuated diaphragm pump. By employing the device of the present invention, the same type of pump driven by different operators, provides the relatively consistent flow; due to the hollow body to maintain the suction effect, the exhaust process is carried out continuously.