Patent ID: 8286822

Claim:
A valve body disposed outside a chamber, which opens and closes sealing airtightly an opening of the chamber, said opening being disposed on a wall of the chamber, comprising: a base body which moves with respect to an outer wall surface of the chamber, disposed in a periphery of the opening according to operations of opening and closing the opening of the chamber; a seal member disposed on a surface of the base body opposing to the outer wall surface of the chamber, which comes into contact with the outer wall surrounding the opening and seals airtightly between the inside and outside of the chamber by contact when the valve body seals the opening, the seal member being comprised of an elastic material; and a cover detachably disposed in an inner periphery of the seal member on the surface of the base body, which presses at least a portion of the seal member to the surface of the base body and determines the position of the seal member, wherein the seal member further comprises: a first seal portion which is disposed in an outer periphery of the cover and surrounds the same, having a projection having a projected curved surface that is sandwiched between the outer wall surface of the chamber and the base body and comes into contact with the outer wall surface to seal airtightly between the inside and the outside of the chamber; an overhang extending towards an inner side of the seal member from the first seal portion, which is engaged with and pressed onto the surface of the base body by the cover when the cover is disposed on the surface of the base body, the overhang including a second seal portion which is sandwiched between the surface of the base body and the cover that is disposed on the surface of the base body and sealing airtightly the inside and the outside of the opening of the chamber when the valve body closes the opening.