Filter roof

Claim 1

IN COMBINATION WITH A FILTER BED FOR USE IN THE TREATING OF WASTES, UNDERDRAIN MEANS FO RSUPPORTING SAID FILTER MEDIA AND FOR PERMITTING AIR TO PASS THROUGH SAID FILTER MEDIA TO VENTILATE THE LATTER, A FILTER BED COVER POSITIONED OVER THE FILTER BED AND COMPRISING A BODY OF RIGID MATERIAL HAVING A BOTTOM AIR OPENING OF RELATIVELY LARGE DIAMETER FORMED AT ITS LOWER END ADJACENT SAID FILTER BED AND A TOP AIR OPENING OF RELATIVELY SMALL DIAMETER FORMED AT ITS UPPER END, THE DIAMETER OF SAID BOTTOM AIR OPENING BEING SEVERAL TIMES LARGER THAN THE DIAMETER OF SAID TOP AIR OPENING, SAID BODY OF RIGID MATERIAL TAPERING CONTINUOUSLY UPWARDLY AND INWARDLY FROM THE BOTTOM AIR OPENING TO THE TOP AIR OPENING SUCH THAT THERE ARE NO SUDDEN CHANGES OF AIR FLOW TO CAUSE SUDDEN ACCELERATIONS NORMAL TO THE DIRECTION OF AIR FLOW, SAID BODY PROVIDING AN INNER CONVEX SURFACE IN THE VERTICAL PLANE DEFINING A CONTINUOUS ENCLOSURE HAVING A HORIZONTAL CROSS-SECTION WHICH DECREASES AS A FUNCTION OF THE HEIGHT OF SAID BODY TO ENHANCE AND PROVIDE UNIFORMITY TO THE FLOW OF AIR THROUGH THE FILTER MEDIA IN THE FILTER BED, THE HORIZONTAL CROSS SECTION OF SAID BOFY AND SAID AIR OPENINGS BEING SUBSTANTIALLY CIRCULAR.