Patent ID: 8602383

Claim:
A suck-back valve, in which a piston and a valve body that receive fluid pressure for an open/close operation are linked via a shaft portion, and an open/close valve that carries out the open/close operation of the valve body by the fluid pressure is provided with a suck-back function, wherein a suck-back chamber formed in a valve internal channel of the open/close vale and an open/close operation portion that operates the piston are separated by a diaphragm that is linked to and integrally operates with the shaft portion; the shaft portion is divided into a valve-body-side shaft portion and a piston-side shaft portion, and the piston-side shaft portion is loosely fitted to the valve-body-side shaft portion, allowing for independent movement in an axial direction; and during the closing operation of the valve body, a two-step operation is carried out, including a valve closing operation step in which the shaft portion, along with the piston and the diaphragm, moves to the fully closed position of the valve body, and a suck-back operation step in which the piston pulls on the loosely-fitted piston-side shaft portion to disengage the loosely-fitted piston-side shaft position from a diaphragm base portion and the valve body, thereby increasing the volume of the suck-back chamber.