GB966394A - Improvements relating to gravity filters - Google Patents

Abstract

966,394. Filters. CANDY FILTER CO. Ltd. Jan. 30, 1963 [Jan. 30, 1962], No. 3524/62. Heading B1D. In a gravity filter in which a granular filter bed is disposed above a floor incorporating means for collecting filtered liquid and for distributing cleansing liquid, an upward flow of cleansing liquid is passed through the bed at a rapidly pulsating rate so that the filter bed is caused alternately to expand and contract by amounts which are insufficient to cause filtering media to be carried away with dirt entrained in the cleansing liquid. In one embodiment, Fig. 1, a rapid gravity filter incorporates a rectangular container 1 holding filter bed 2 of e.g. sand or anthracite supported on grid 3 forming the floor of the container. Sill 4 forms with one wall a trough 6 for disposal of cleansing liquid. The filter is cleaned by delivering cleansing liquid from a pump or raised tank (not shown) via pipe 7 to underdrain 5. The otherwise steady flow of liquid is pulsated by operating a reciprocating plunger, diaphragm or air-vessel 8 at e.g. 25-200 pulses/minute. The momentary variations in pressure under the filter bed and corresponding variations in flow rate cause alternating expansion and contraction of the bed. Pipe 7 is of such length that the flow of liquid from pump or raised tank is unaffected by the variations in pressure. In a modification, Fig. 2, the reciprocating member 8 is connected to underdrain system 5 by a separate pipe 9.