Patent ID: 8740011

Claim:
A valve which contacts with a wall surface around an opening disposed on a chamber and opens and closes the opening in an air-tight manner, comprising: a main body which moves confronting the opening closer thereto and separating away therefrom; a seal member disposed on a surface of the main body in a side on which the main body confronts the opening, the seal member being circular shaped and, when the valve closes the opening in the air-tight manner, contacting the wall surface around the opening in being sandwiched between the surface of the main body and the wall surface so that the seal member can seal inside of the opening; and a cover disposed on the main body in the side on which the main body confronts the opening, the cover pressing the seal member toward the main body to hold a position of the seal member on the surface of the main body, wherein the seal member includes a first projecting portion having a curved surface which contacts with the wall surface and an overhang extending from the first projecting portion along the surface of the main body which is engaged with and pressed onto the surface of the main body by the cover when the cover is disposed on the surface of the main body, and wherein the overhang includes a constriction portion, a thickness of which is smaller than that of the first projecting portion.