PURPOSE:To obtain durability and reliability, by providing a seesaw type valve plate part having a valve body provided thereto on one side thereof and a stopper part capable of fixing the valve seat part opened and closed by the valve body and the valve plate part at least at an open position. CONSTITUTION:A valve plate part 3 is fixed at an open position P1 by inserting the engaging protruding part 20 thereof in an engaging recessed part 21 and engaging a constricted part 19 with a spring 23. A valve body 2 is separated from a valve seat 4 by the seesaw function of the valve plate part 3. Therefore, an inflow pipe 15 communicates with an outflow pipe 16 through the route of the arrow H shown by the dotted line in a drawing. When the valve plate part 3 is pushed from above on the side of the valve body 2 from this state by a hand, the valve plate part 3 is rotationally displaced to be changed over to the state of a closed position P2. In this state, the valve body 2 is inserted in the valve seat 4 to block a flow passage. By this constitution, trouble is reduced, and excellent durability and high reliability can be obtained. Further, certain operation is ensured and an opening and closing position can be confirmed certainly and easily and the prevention of an operative mistake is achieved.
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