Patent ID: 8251345

Claim:
A suck-back valve in which an open/close valve that includes an elastic member that biases a valve piece in an opening/closing direction carries out a valve piece opening/closing operation by receiving fluid pressure on an open/close operation portion that is provided with a piston main body and a piston biasing member and is provided with a suck-back function to prevent leakage during the fully closing operation, the suck-back valve comprising: a suck-back chamber formed in a valve internal channel in the open/close valve; a piston shaft portion that connects the piston main body and an open/close pressuring member that moves in the suck-back chamber in the axial direction to apply pressure to the valve piece; and bellows that accommodate the piston shaft portion inside, separating the open/close operation portion from the valve internal channel, and that are connected to the open/dose pressuring member at one end and are supported by a casing at the other end; wherein a two-step operation is carried out at the time of closing operation of the valve piece, including a valve closing operation step in which the piston shaft portion, along with the piston main body and the open/close pressuring member, moves to the fully dosed position of the valve piece, and a suck-back operation step in which the piston shaft portion and the open/close pressuring member further move from the fully closed position of the valve piece so as to increase the volume of the suck-back chamber.