GB953239A - Improvements in rotary filters - Google Patents

Abstract

953,239. Rotary vacuum filters. DAVEY, PAXMAN & CO. Ltd. Sept. 26, 1962 [Oct. 17, 1961], No. 37157/61. Heading BID. In a rotary vacuum filter, the pressure medium is used to inflate pressure elements acting mechanically to press the filter cake against the filter medium at appropriate points in the operating cycles. Slurry is fed to a filter trough 2 where it may be kept in suspension by a mechanical agitator. A vacuum is applied to the inside of the filter leaves 1 via ports 4 which communicate with a hollow trunnion (not shown) for the axial rotating member 5, application of the vacuum being controlled by an automatic valve head of known type. Thus liquid is drawn through the filter medium 3 while the solids build up as a filter cake on the flat surfaces of the rotating leaves 1. As the cake emerges from the trough, the action of the internal vacuum in removing moisture from the cake is enhanced by inflation of the inflatable pressure elements 7, made of reinforced rubber or other flexible material impervious to gas or liquid at the required working pressures, which rotate continuously and uninterruptedly with the trunnion and leaf assembly, their interior spaces communicating with an internal pressure line 8, thus exerting a pressure of up to several atmospheres on either side of the cake. The filter leaves may have a selvedge consisting of an impervious non-filtering surface which acts as a seal between the leaf and the pressure element. On completion of the compression of the filtered material and just before the cake discharge point is reached the pressure elements are deflated by releasing the internal pressure or by pumping out and the cake is then discharged, e.g. by blow-back air or steam pressure applied to the inside of the filter leaves. The inflatable pressure elements may be filled with liquid instead of gas if desired. In an alternative form, not shown, the pressure elements are stationary and the leaf assembly rotates intermittently. Thus non-rotating pressure elements may be withdrawn from the spaces between the rotating leaves for part of the filtering cycle and inserted into these spaces for other parts of the cycle.