| 摘要 |
A seat retainer (14) fitted with a ball seat (15) is provided on one or both sides of a ball (12) having a through hole (12a) provided inside a body (11), the ball (12) is provided so as to be rotatable by a stem (13), and the ball seat (15) is prevented from flying out into a fitting groove (32) formed in the seat retainer (14), and is fitted in a free state. Excess pressure due to abnormal pressure increases in a cavity (35) when fully open or fully closed causes the seat retainer (14) to move in an opposite direction from the ball (12) due to a self-sealing force making use of this pressure, and excess pressure that has flowed to the rear surface side of the ball seat (15) inside the fitting groove (32) pushes the ball seat (15) toward the ball (12), and is relieved to a flow channel via a communication part (40) provided between the inner circumferential surface (27) of the ball seat (15) and the fitting groove (32). |
