| 摘要 |
A controller ( 10 ) provides water to outlet ( 22 ) from a supplementing water supply (e.g. from a rainwater tank) attached to passage ( 18 ) in preference to a main water supply (e.g. from a mains water supply) attached to passage ( 14 ). If there is insufficient supplementing water to meet demand, then mains water flows through passage ( 14 ), around partition ( 36 ) and to outlet ( 22 ). If there is sufficient supplementing water for the demand, a supplementing water pump is activated, and the pressure of supplementing water in passage ( 18 ) is raised above a threshold level at which it is able to move piston ( 28 ) against mains pressure to seal against valve seat ( 34 ) and block the mains supply, so that supplementing water can flow to outlet ( 22 ) via one-way valve ( 42 ). Piston ( 28 ) has a larger effective area ( 28 b) at its low pressure end than at it high pressure end ( 28 a), so that the supplementing water threshold pressure level for moving the piston ( 28 ) to block the main supply passage ( 16 ) is less than mains pressure. Mains water is supplied if there is insufficient supplementing water or if the pump fails or there is a power outage, otherwise supplementing water is supplied.
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