GB502765A - Improvements in or relating to supplementary filters for gas masks and the like - Google Patents

Abstract

502,765. Filtering gases. SOC. ITALIANA PIRELLI. March 9, 1938, No. 7413. Convention date, March 17, 1937 [Class 8 (ii)] [Also in Group VI] A supplementary filter of a gas mask, for use with the main filter which comprises a canister having an opening in the centre of one of its end walls through which air enters, is of flat form, having an axial length considerably less than its diameter, and is provided with means for effecting a quick and detachable connection to the main hfter over the opening by engagement of the end wall in or near the opening, the connecting means being such as to be applicable without structural modification of the end wall. The filtering material of the supplementary filter may have different characteristics from these of the main filter. In Fig. 1, the supplementary filter consists of two elements 2, 3 screwed together and clamping perforated plates 5, 8, packing rings 6, 7 and filter element 9 of fabric, felt or paper. In Fig. 2 the filter element 13 is held between elements 10, 11 by a ring 12 ; an adhesive or plastic sealing material may be used at the joint. In each construction, a screw-threaded connection 4, 14 is formed on the upper wall for connection with. for example, an element 20 arranged to be fixed over the central opening in the end wall of the main canister 21 by bridge pieces 22, 23 connected by screws 24 or by binding. In another construction, a part corresponding to element 20 is formed with a threaded extension of smaller diameter for screwing into the opening in the main filter, a packing ring being disposed between the end wall of the main filter and the shoulder on the connecting piece.