| 摘要 |
<p>Main water supply pipes to houses and the piping (6) within the house are usually well protected from frost. However, householders often extend the supply system to a garage or other outhouse, and the additional piping may be above ground and liable to freeze up and burst. The present system automatically shuts off the additional supply and drains the external pipe, if freezing temperatures are detected. In freezing conditions, the temp. detector (11) triggers a control unit (10) which then energises two solenoids: one which operates a shut-off valve (8) and another which opens a drain cock (9) to empty the exposed pipework (6'). When the temp. rises above freezing point, the drain is closed and the supply reconnected. In its simplest form, the detector is a conventional adjustable bi-metallic thermostat and the controller is a simple transformer and rectifier circuit. Another version uses a temp. sensitive resistance and amplifier to operate a control relay.</p> |
