Pressure filter

Claim 1

A PRESSURE FILTER HAVING (A) A PRESSURE-WITHSTANDING CHAMBER WITH AN INLET FOR LIQUID TO BE FILTERED AND AN OUTLET FOR FILTRATE, AND WHEREIN A PRE-COAT LAYER OF PARTICLES OF A FILTER AID IS TO BE DEPOSITED ON THE OUTER SURFACE OF A TUBULAR LIQUD-PERVIOUS FILTER AID RETAINER BEFORE FILTERING THE LIQUID TO BE FILTERED THROUGH THE FILTER AID, AND PERIODICALLY FILTRATION IS TO BE STOPPED AND THE FILTER AID AND FILTERED OUT MATERIAL ACCUMULATED ON THE OUTER SURFACE OF SAID RETAINER IS TO BE REMOVED BY BACKWASHING OR BLOWBACK; AND (B) AT LEAST ONE FILTER UNIT ASSEMBLY WITHIN SAID CHAMBER INTERMEDIATE SAID LIQUID INLET AND FILTRATE OUTLET; SAID AT LEAST ONE FILTER ELEMENT COMPRISING (I) A RIGIDLY SUPPORTED TUBULAR LIQUID-PERVIOUS FILTER AID SUPPORT-RETAINER TO ENABLE DEPOSITING AND RETAINING ON ITS EXTERIOR SURFACE A PRE-COAT LAYER OF FILTER AND BY FILTRATION FROM A LIQUID PRE-COAT ING MIXTURE FED INTO SAID CHAMBER THROUGH SAID INLET; (II) A CENTER TUBE SPACED DIRECTLY AWAY FROM THE INNER SURFACE OF SAID RIGIDLY SUPPORTED FILTER-SAID SUPPORT-RETAINER THEREBY TO PROVIDE BETWEEN SAID INNER SURFACE OF SAID SUPPORT-RETAINER AND THE EXTERIOR SURFACE OF SAID CENTER TUBE AN UNOBSTRUCTED ANNULAR PASSAGE ZONE FOR PASSAGE OF FILTRATE DIRECTLY FROM SAID INNER SURFACE OF SAID CENTER TUBE AND FOR BACKWASHING LIQUID TO PASS FROM THE LATTER DIRECTLY TO THE INNER SURFACE OF THE SUPPORTRETAINER; SAID CENTER TUBE SERVING TO RECEIVE AND LEAD FILTRATE AWAY FROM SAID ANNULAR PASSAGE, AND IN THE BACKWASHING STAGE TO RECEIVE BACKWASHING LIQUID FED INTO SAID CHAMBER THROUGH SAID OUTLET FOR FILTRATE; (III) A CLOSURE AT EACH END OF SAID ANNULAR PASSAGE AND EXTENDING FROM SAID CENTER TUBE TO SAID SUPPORT-RETAINER; AND (IV) EXTENDING THROUGH THE WALL OF SAID CENTER TUBE A PLURALITY OF LIQUID-PASSAGE ORIFICES, THE TOTAL OPEN AREA OF ALL OF THEM BEING SIGNIFICANTLY LESS THAN, WITHIN THE RANGE OF FROM ABOUT ONE-THIRD TO ABOUT FOUR-FIFTHS OF, THE AREA OF THE CROSSSECTION OF THE INTERIOR OF THE CENTER TUBE TAKEN PERPENDICULAR TO ITS AXIS, SAID ORIFICES BEING DISPOSED SUBSTANTIALLY UNIFORMLY OVER THE LENGTHS OF THE SURFACE AREA OF SAID CENTER TUBE WALL; AND CENTER TUBE AND TUBULAR SUPPORT-RETAINER ENCIRCLING IT BEING AT LEAST ABOUT THREE FEET HIGH; AND SAID UNIT ASSEMBLY THEREBY ENABLING PRODUCING BY FILTRATION A DEPENDABLY UNIFORM DEPOSIT OF FILTER AID ON THE TUBULAR SUPPORT-RETAINER AS WELL AS OBTAINING BY BACKWASHING SUBSTANTIALLY COMPLETE REMOVAL OF THE FILTER AID AND ANY FILTERED OUT MATERIAL THEREFROM.