Abstract: In an air cleaner employing a pleated paper filter element in the form of a frustrum of a cone mounted in a tubular air cleaner casing having a first opening axially thereof communicating with the inside of said element at the relatively wide end of said frustrum and a second opening in the cylindrical wall of said casing communicating with the outside of said frustrum in the vicinity of the relatively narrow end thereof, the axis of said element is tilted relative to the axis of the cleaner casing away from said second opening, whereby the radial clearance between the filter element and said opening is increased for a given filter element without increasing the size of the casing.

Abstract: A generally tubular pleated paper filter element is constructed in the form of a frustrum of a cone having an aspect ratio (the ratio of element length to base diameter) in the range 1.5 to 2.5 and an included angle in the range 2 to 5 degrees.

Abstract: An air cleaner comprises at least two pleated paper filter elements each having the configuration of a frustrum of a cone and mounted in side-by-side relation in a casing with their relatively wide diameter ends in sealing relation to a common, impermeable baseplate means dividing said casing into two discrete portions, said baseplate means having openings defined therein to provide direct communication between one of said portions and the insides of said elements, impermeable means for closing the relatively narrow diameter ends of the elements, together with an aperture in the casing in each of said portions, whereby in use, air entering one of said apertures can pass to the other aperture only through said filter elements. The impermeable means for closing the narrow ends of the elements is preferably a blanking plate integral with each of said ends.

Abstract: Gas filtration apparatus comprises a filter element mounted in a casing having an inlet and an outlet so disposed that gas flowing from inlet to outlet is constrained to pass through the filter element, an audible warning device operable by gas flowing through the inlet and means responsive to the difference between the gas pressure at the inlet and the gas pressure at the outlet and arranged to cause the audible warning device to operate whenever said difference exceeds a predetermined value.