A device for controlling the activation of an apparatus by a motor, intended to be inserted between, the operation output of the motor and the operation input of the apparatus whose activation is to be controlled. The device includes: --a blade pump having a rotor, at least one blade carried by this rotor and a rotary body forming a pumping chamber missing an outlet, and one of the component parts, among the rotor and the rotary body, being connected to the operation output of the motor, whilst the other of these component parts is connected to the operation input of the apparatus to be controlled; --and a supply intended to supply liquid to the pumping chamber.