GB2154145A - Flexible hoses - Google Patents

Abstract

An airman's oxygen mask hose comprising an injection moulded hose (10) of silicone or butyl rubber and having its crush resistance increased by the provision of rigid, separate, light-weight rings (14) individually located in the troughs of the corrugations (12), preferably both on the inside and the outside of the hose. <IMAGE>

Description

SPECIFICATION Improvements in Flexible Hoses This invention relates generally to flexible hoses and in particular to an airman's oxygen mask hose.

Pilots and other airmen, more particularly in military aircraft, wear an oxygen mask which is supplied with oxygen via a manifold supported on the body in the region of the chest. The manifold connects with the mask through a flexible hose, typically about 33 cm (13 in) long and 1.9 cm (4 in) internal diameter. This flexible hose is referred to herein as an airman's oxygen mask hose.

The flexible hose in question has to meet a number of relatively exacting requirements which to some extent conflict with one another.

Firstly the hose must be flexible. For this reason the hose is currently formed as a corrugated hose of natural or synthetic (polyisoprene) rubber.

Secondly, it must be crush resistant and is therefore produced, typically by forming over a mandrel, with fairly thick walls. However, the resultant hose now has a relatively substantial mass, sufficient in the presence of large G-forces to restrict the head manoeuvrability of the airman and possibly to cause separation of the hose from the face mask during ejection.

It has been proposed that the problem of large mass should be avoided by forming the corrugated hose by injection moulding. A hose formed by such a a process would have reduced mass compared to the conventional hose, but whilst retaining high flexibility would have very poor crush resistance insufficient, for instance, to prevent risk of the oxygen supply being completely cut off if the airman should trap the hose under his arm or possibly in a seat harness. In addition, such a hose would be sufficiently "soft" to present risk of non-return to its natural condition on occurrence of a localised depression or kinking, which characteristic is also intended to be embraced by the general property of "poor crush resistance".

Furthermore proposals have therefore been made to increase the crush resistance of an inherently non-crush resistant but lightweight corrugated base. One such proposal is to embody a helical stiffening wire within the corrugated wall of the hose during its production. It is, however, almost impossible to practice to maintain manufacturing tolerances with sufficient accuracy to ensure that the stiffening wire is properly and satisfactorily embedded in the hose wall over the entire length of the hose; if it is not, the hose will have one or more points of inherent weakness with accompanying risk of fracture.

Other possibilities, for example known from techniques for stiffening and strengthening corrugated hoses used in other fields, in general lead to an unacceptable reduction in flexibility and expansibility of the hose and/or to an increase in mass leading back to the original position.

It is an object of this invention to provide an airman's oxgyen mask hose which provides a solution to the above descriebd problem.

According to the invention there is provided an airman's oxygen mask hose which comprises a hose with corrugated exterior and interior walls and having its crush resistance increased by the provision of separate, rigid reinforcing rings individually located in at least some of the corrugation troughs on the inside and/or outside of the hose throughout its length.

The provision of the individual reinforcing rings enables an inherently low mass hose, for example formed of silicone or butyl rubber, to be rendered crush resistant without loss of flexibility and without any very substantial increase in overall mass.

In a practical embodiment, O-rings are located in every trough both on the inside and outside of the hose. These O-rings may conveniently be formed of a a plastics material steel, aluminium or a conveniently lightweight alloy. Alternatively, however, it may be possible to locate such O-rings only in every other trough or even every third trough along the length of the hose, for example so that the rings on the inside are in uniformly staggered relationship in the axial direction relative to the rings on the outside.

The O-rings are dimensioned to fit snugly into the bottom of the troughs and, self-evidently, the 0rings for fitting inside the hose will be slightly greater in diameter than those fitting outside the hose. In a practical example, the O-rings are of a squared cross-sectional shape, but round crosssectioned rings may sometimes be preferred.

O-rings both on the inside and the outside of the hose are to be preferred, because the hose is orientated near vertically in use. If rings are located only on the outside, a momentary failure in the oxgyen supply which may cause the hose to collapse could possibly result in at least some of the rings slipping to the bottom of the hose.

Correspondingly, if rings are located only on the inside, a sudden expansion of the hose, as due to an excess exhalation by the user, could likewise possibly result in at least some of the rings slipping to the bottom of the hose. In either case, however, it may be practicable to overcome this problem by adhering the rings, either on the inside or on the outside, in the troughs in the internal or external wall of the hose. Alternatively, the problem may be avoidable by locating only a relatively few rings either on the inside or on the outside, the rings on the other side serving for the main purpose of increasing crush resistance.

Yet again, whilst O-rings, i.e. unbroken or continuous rings, have been referred to, it may be possible, in some circumstances, even though less desirable in general, to employ broken rings. These will preferably be either of C-form or with overlapping ends, so as to avoid possible rubbing together of the abutting ends of complete but broken rings, especially as the noise generated by this rubbing together may interfere with the airman's communications system or radio.

Unbroken or continuous rings, referred to herein as O-rings, are also to be preferred in order to avoid any possible risk of a ring and damaging the hose wall.

It is an especially advantageous feature of the invention that it enables the hose to be injection moulded, more especially of silicone or, when necessary butyl, rubber. This technique, not heretofore practicable for relatively thin walled airman's oxygen mask hoses mandrel formed of natural rubber of synthetic polyisoprene rubber, results in a low mass hose which has walls of very uniform thickness throughout the length of the hose, but walls which are relatively thin compared to the walls of the known mandrel formed hose.

In practice, a preferred injection moulded hose has a wall thickness of about 1.1 mm (44 thou), and has a pitch offourcorrugationsto 2.5 cm (1 inch).

The radial depth of the corrugations is preferably, in practice, appreciably less, of the order of one half of the depth of the corrugations in the known mandrel formed hose.

A practical example of airman's oxygen mask hose in accordance with the invention will now be described with reference to the accompanying drawing, in which the hose is illustrated somewhat diagrammatically, with some dimensions exaggerated for reasons of clarity.

The illustrated hose is specifically intended to connect from the manifold to the oxygen orface maskworn by a pilot or other airman in a military aircraft. Such a hose typically has a length of about 33 cm and an internal diameter of about 1.9 cm.

Only a part of the length is illustrated.

The hose, generally referenced 10, is injection moulded of silicone (or possibly butyl) rubber with a uniform wall thickness of about 1.1 mm. It is formed with corrugations 12, internally and externally, at a pitch offourto 2.5 cm.

This basic hose produced by injection moulding as described above inherently has very good flexibility, and is of low mass, but has poor crush resistance.

To provide crush resistance, aluminium O-rings 14 are individually located in the troughs of the corrugations, both on the inside and outside of the hose, along the entire length of the latter. The O-rings 14 are dimensioned to be a close but non-distorting fit in the corrugations, and are readily fitted into position, first on the inside and then on the outside, starting from the middle of the length of the hose. As illustrated an O-ring 14 is fitted in the trough of every corrugation, both on the inside and the outside, but this will not always prove essential, provided that sufficient O-rings are fitted to impart crush resistance along the entire length of the hose.

The O-rings impart crush resistance to the hose without reducing flexibility, and with only a small increase in mass, thus providing a satisfactory and relatively inexpensive solution to the aforedescribed problem which arises with the known airman's oxygen mask hose.

Claims (10)

1. An airman's oxygen mask hose which comprises a hose with corrugated exterior and interior walls and having its crush resistance increased by the provision of separate, rigid reinforcing rings individually located in at least some of the corrugation troughs on the inside and/or outside of the hose throughout its length.

2. A hose according to claim 1, wherein the rings are evenly distributed along the length of the hose.

3. A mask according to claim 2, wherein the rings are located in every corrugation trough, either on the inside of the hose or the outside thereof or both.

4. A hose according to any of claims 1 to 3, wherein the rings are O-rings.

5. A hose according to claim 4, wherein the rings are made of metal or a plastics material.

6. A hose according to any of claims 1 to 5, formed of silicone or butyl rubber.

7. A hose according to any of claims 1 to 6, formed by injection moulding.

8. A hose according to any of claims 1 to 7, having a wall thickness of about 1.1 mm.

9. A hose according to claim 8, having corrugations at a pitch of about four to 2.5 cm.

10. An airman's oxygen mask hose substantially as hereinbefore described with reference to the accompanying drawing.