Patent GB-511986-A (GB)
Title: Improvements in or relating to air-filtering units for respirators
IPC: A62B23/02
Filed: 1938-03-25
Abstract: 511,986. Respiratory appliances. MINE SAFETY APPLIANCES CO. March 25, 1938, No. 9193. Convention date, March 26, 1937. [Class 81 (ii)] In apparatus for respiratory protection against dust, smoke and the like, and comprising, for example, a rubber or like mask 1, Fig. 3, secured to the face by straps 31 and having inturned bevelled edges 2 and a central depending exhaling valve 34 of the flutter type, one or more circular air-filtering canisters 3 are provided, for example, one on each side of the mask, and a large filter surface is presented by providing in each canister two or more filter elements which are clamped at their edges and all but one of which have an outlet opening connected with an outlet port for the canister, the sheets being spaced from one another by perforated means, such as spiders, extending completely across their surfaces. As shown, each canister 3 has an inturned flange 13 between which, and a rib 14 on a screw-on or like cover 6, are clamped two disc-like filter elements 11, 12. A spider 36 in the form of a slightly coned spoked wheel, is clamped peripherally between the elements and spaces them apart at the centre. Element 11 has a central aperture of which the edge is clamped between flanges on a central outlet tube 17 and an inner tube 18 secured to it as by a bayonet joint 21, 22. Tube 17 is clamped to portions 29 of the mask which are offset to prevent collapse thereof under suction. Air-inlet apertures 27 are provided both in the cover 6 and in the base of the canister 3. The elements 11, 12, preferably comprise filter paper of pore size selected, or prepared by treatment as described in Specification 450,369, for the purpose in view. Alternatively, a layer of felt 36 acting as a coarse filter may be combined with a prepared paper filter 37. In a modification, 'in addition to elements 11, 12, which are separated by a spider the hub of which presses on and extrudes within tube 17 thus replacing tube 18, a third element is provided, also clamped at its centre by the spider hub and itself having a spider which presses its outer edge against the periphery of the base 3. In this construction the apertures 27 in the base are replaced by apertures in the cylindrical surface of the canister the air entering through which passes through element 11 to tube 17 and also through the third filter to lateral ports in the tube. In the construction of Fig. 6 a casing 74, and a stepped screw-on cover 58 therefor, house filter elements 57, 61, 62, 71, clamped at their peripheries by spiders 59, 63, 69, and by the step 73 of the cover. The inner ring 64 of spider 59 extends within the outlet tube 56 and clamps the inner edges of elements 61, 62, and spider 63. The inner ring of spider 69 clamps the inner edge of filter 71 against a shoulder 72. Air enters through apertures 76 in the end and the central step of the cover, and in the base of the casing, and passes through the filter elements to the end of tube 56 and to lateral apertures 77 therein. In a further modification having a pair of elements mounted substantially as in Fig. 3 the tube 17 is arranged eccentrically and the spacing spider, correspondingly eccentrically constructed and having a ring extending into tube 17, has radial fingers bent outwardly to assist in spacing the elements from one another. The spider may alternatively be secured by bent-up lugs to a ring having cross-pieces which are attached to the end of tube 17 by engagement with bayonet slots therein, the tube being cut away between the slots for the passage of air.