A screen for cleaning a pulp suspension includes a stationary installation in the infeed area between the infeed branch and the free end of the rotor. The chargerdischarger connects a plurality of secondary batteries, and charges one secondary battery by electric power discharged by another secondary battery. A fuel inlet is formed at a lower side of the side wall to face upwardly to allow the fuel to gradually enter the lower chamber so that an inner pressure in the fuel tank increases by entering the fuel into the lower chamber after the fuel reaches the fuel inlet. When the first and second speed sensors are operative, the first and second brakes can be controlled according to a first routine. The interconnection member includes at least a rigid connecting rod articulated on one side to the nut screw and on the other side to the driving member, which is able to assume different tilts when the distance between the driving member and the nut screw changes. The cooling air, drawn into the air duct systems by respective direct drive fan means integrated in the air-cooled engine and generator, exits through respective air outlet ducts from the enclosure.