| 摘要 |
<p>A valve 10, for relieving ground water pressure on a swimming pool for containing pool water. A body 30 defines a flow path. An element 20 is mounted to be moved in a direction from a position, in which at least one feature 22 of the element co 5 operates with at least one feature 33 of the body to form a sealing arrangement to block the flow path to retain the pool water, to a position in which the flow path is open to allow ground water into the swimming pool. The sealing arrangement defines an effective area over which the ground water pressure acts to drive the element in the direction, and an effective area over which pool water pressure acts to drive the 10 element opposite the direction. The co-operable features are configured such that a ratio, of the effective area over which the ground water pressure acts to the effective area over which pool water pressure acts, has a value of at least 0.9. 34 C34b 3434a</p> |
