| 摘要 |
PURPOSE:To prevent generation of water hammer using a pressure-balanced type ball tap, by a method wherein only an inner valve is closed before valve lift is reduced to 0, and thereafter an outer valve is closed. CONSTITUTION:The clearance C1 between the outside diameter of an inner valve packing holder 7 and the inside diameter of an inner valve seat 13 is set to be as small as possible to such a range that the packing holder 7 can be slid in the inner valve seat 13. The radial clearance C2 of an outer valve packing holder 11 is so set that an outer packing 10 is evenly seated on an outer valve seat 14 when closing the valve. Though a pushing-up force exerted on the outer valve by a water flow is smaller than a pushing-down force exerted on the inner valve while the valve lift 2 is large, it is gradually increased as the valve lift 2 is reduced, and the pushing-up force and the pushing-down force coincide with each other when the valve lift 2 is reduced to 0. Accordingly, water hammer is prevented from occurring. |
