| 摘要 |
A ball valve includes a valve casing accommodating therein an upstream ball seat and a downstream ball seat and defining a cavity between the two ball seats, a ball provided with a through hole, accommodated in the cavity and brought into sealing contact with the two ball seats at the outer periphery thereof, a valve stem having one end thereof fixed to the ball, a valve handle fixed to the other end of the valve stem, a check valve accommodated in the through hole of the ball and biased toward the upstream side, a path formed on the ball and, when the ball valve is closed, causing the downstream side and the cavity to communicate with each other, and a connection port formed on the valve casing so as to communicate with the cavity and having a free end thereof connected to one end of a nipple having the other end thereof covered with a cap. The ball opens and closes the ball valve through the valve stem by a rotating operation of the valve handle.
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