Abstract: A valve head is actuated by a resetting spring, on one hand, and on the other hand, by the rotor of a motor acting upon a screw and nut assembly. The rotor of the motor is axially coupled to a plunger of an electromagnet. Said valve head, the rotor of the motor, and said plunger of said electromagnet are thus jointly displaceable in the axial direction. In the resting position, or in the case of a power breakdown, said valve is closed by a spring, and said rotor as well as said plunger of said de-energized electromagnet are axially displaced. In the working position, said plunger is attracted and maintained in its working position by a pole piece of said electromagnet, and said rotor is also maintained in its working position in order to regulate the position of said valve head by means of said screw and nut assembly.