| 摘要 |
PURPOSE:To provide high air-tightness and low operating torque by controlling the pressure in a pressure chamber between the seat ring and valve body by means of a selector valve. CONSTITUTION:When a ball valve of trunnion supporting type is in closed position, seals N1, N2 are pressed to a ball L strongly by the piston force of pressure chambers B, D to provide high air-tightness. When the valve is to be opened, inside the pressure chamber becomes negative pressure by operation of a five-way valve V, so that the seals N1, N2 are separated from the ball L, when there is no friction between the seals N1, N2 and ball L with only friction at the ball supporting part remaining. This provides high air-tightness and reduces the operating torque greatly.
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