Patent attributes
A trunnion-type ball valve including a seat retainer (14) attaching a ball seat(s) to at least one side of a ball (12) having a through hole (12a) provided in a body (11). The ball is turnably provided via a stem (13), and the ball seat is attached in a protrusion-prevented and free state in an attachment groove formed in the seat retainer. An excessive pressure due to an abnormal pressure rise in a cavity upon full close or upon full open is configured to be relieved into a flow channel via a communication part provided between an inner peripheral surface of the ball seat and the attachment groove by moving the seat retainer in a direction opposite to the ball by self-tension utilizing the pressure and pushing-out the ball seat to a ball-side by the excessive pressure flowed into a rear-surface side of the ball seat in the attachment groove.
