| 摘要 |
A stopper for selectively blocking a drain to the passage of water. The drain has an inlet, an outlet and a substantially cylindrical throat between the inlet and outlet. A control means is provided for selectively feeding control fluid under hydraulic pressure to the cylindrical throat whereupon an expandable bladder located within the cylindrical throat selectively expands in fluid communication with the control fluid to block the drain and thus act as a stopper.
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