PURPOSE: To remove the necessity of a preload spring and to improve the efficiency of the titled equipment by incorporating the 1st and 2nd ajdustable over load protecting means into the fluid rooms of the 1st and 2nd control diaphragms.

CONSTITUTION: The 1st control diaphragm 36 is located so as to cross a cyclic recessed part 34 and the peripheral part of the diaphragm 36 is fitted to the body of an outgoing trunk equipment by welding e.g. The 1st fluid passage 38 is incorporated in the 1st backup plate 24 to connect both the sides of the backup plate 24. The 2nd backup plate 30 is provided with the 2nd control diaphragm 68 related to the plate 30, the 2nd diaphragm supporting plate 70, etc. Thus the attachment of these overload protecting means makes it possible to remove the necessity of a preload spring and improve the efficiency of the equipment.