Abstract: A valve for a respirator has an elastomeric valve member (18) of generally dished form with an annular channel (25) around its central portion (24). The member (18) is secured at its center by a shouldered conical stem (19) and seals round its periphery (23). The channel (25) allows a sudden collapse of resistance to opening force in the direction of the arrow A above a predetermined amount, but a positive biassing action towards closure. The edges of the channel (26,27) are slightly axially displaced from one another. Both inlet and outlet valves of a respirator may be equipped with such a valve member.

Abstract: Air inhaled into a respirator encounters an air guide positioned inside the face-piece of the respirator which acts as a baffle for the air. The passage between the two contains elongate ridges which are shaped to impede and direct the air and to maintain the spacing of the air guide relative to the face-piece. Because of this, the air guide and face-piece can be made symmetrical, with an air inlet canister and a secondary speech outlet module being applied, in either orientation, to laterally symmetrically disposed apertures in the face-piece.

Abstract: A sight-corrective lens is attached between an eyepiece of a respirator and the eye of the wearer by a monocular mount into which the lens fits as if into a standard spectacle frame. Attachment devices for the mount are apertured lugs on a surround of the eyepiece and tabs on the mount. By making the tab and mount in one position of different tangential width from the tab and mount in the other, a desired unique positioning of the lens is assured. The mount may have a seal ring of which the deformable ridge is pretensioned against the eyepiece by the fitting of the tabs in the lugs to prevent ingress of moisture or particles between them.

Abstract: The pivoted jaws (2,3) of a buckle for a strap (4) are held together by fastening means (22,23) which define a first closed position of the buckle, but which are such as to allow closer approach of the jaws when they squeeze the strap between them. A moment is exerted, if the strap is pulled, between an edge (9) over which it is turned and which is offset from the pivot (10) and this has the effect of causing closer approach of the jaws and thus an increasedly positive hold. Teeth (20) on one of the jaws are of a saw-tooth profile to permit movement of the strap in one direction even when the buckle is closed. Both jaws may be respective one-piece integral plastics mouldings.

Abstract: To achieve highly fluid-tight sealing of a rigid insert into an orifice in flexible material (101), the insert is made in two parts (103, 106) which can be pressed together with purely axial movement, one part deforming slightly relative to the other at least during the movement, until they adopt as a result of interengagement between them a relationship in which they exert a predetermined sealing pressure on the edge portion of the flexible material between their radially extending flanges (108, 109). A bead (102) may be accommodated in an oversize recess (122) in the flanges. A sub-assembly such as an eyepiece (111) is held fluid tight in one (103) of the parts. Detent means (107, 116) are designed to maintain a sealing contact even if the flexible material (101) or sealing ring (118) creep or set. Though the orifice has an endless edge it is not necessarily circular in outline.