GB2432123A

GB2432123A - A breathing apparatus demand valve

Info

Publication number: GB2432123A
Application number: GB0607448A
Authority: GB
Inventors: Nicholas John Foss
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-05-07
Filing date: 2006-04-13
Publication date: 2007-05-16
Anticipated expiration: 2026-04-13
Also published as: GB0607448D0; GB2432123B; GB0509369D0

Abstract

A demand valve for breathing apparatus is provided whereby breathable gas, stored under pressure, is admitted to a face-piece, hood or helmet at a rate that matches the respiratory requirements of the wearer whilst at the same time maintaining a super-ambient pressure within the face-piece. The demand valve has a housing (1) with an outlet port (17) for connection to the face-piece and an inlet connection (9) terminating inside the housing (1) with a conical jet (10, abutting the end face of which is a resilient seating (14) mounted upon a lever (7) affixed to the housing (1) by means of a pivot (8) such that rotation of the lever (7) about the pivot (8) causes the resilient seating (14) to move towards or away from the jet (10), the free end of the lever being engaged with a hook or bridge (6) attached to the rigid central portion (5) of a flexible pressure-responsive diaphragm (4), the periphery of which is sealed to the housing (1) such that changes in pressure within the housing (1) will cause the diaphragm (4) to move inwards or outwards, so controlling the position of the lever (7) and thus the position of the resilient seating (14) with respect to the jet (10). The lever (7) further comprises a vane (16) which deflects the flow of incoming gas away from the diaphragm (4).

Description

A BREATHING APPARATUS DEMAND VALVE

Field of the Invention

This invention relates to demand valves for breathing apparatus, whereby breathable gas, stored under pressure, is supplied to a face-piece, helmet or hood at a rate which matches the respiratory demands of the wearer whilst at the same time maintaining a super-ambient, or "positive", pressure within the face-piece such that the inward leakage of ambient atmosphere is prevented.

Demand valves of the positive pressure type are well known and employ various valve mechanisms to control the flow of breathing gas to the face-piece. The mechanism is typically actuated by movement of a flexible diaphragm having an outer face exposed to the ambient pressure and an inner face exposed to the pressure within the face-piece. When the wearer inhales, the pressure within the face-piece falls, causing the diaphragm to move inwards and actuate the valve mechanism to admit breathing gas to the face-piece at a rate that is proportional to the pressure change within the face-piece. At the cessation of inhalation, equilibrium is restored and the valve closes.

A small super-ambient pressure is maintained within the face-piece by biasing the valve open such that a positive pressure within the face-piece of, say, 2 millibar, is required to move the diaphragm outwardly to close the valve. The biasing is typically achieved by means of spring force applied either to the valve mechanism itself or, more commonly, to the diaphragm. A simple non-return exhalation valve in the face-piece allows the wearer's exhaled breath to pass out to the surrounding atmosphere, the valve typically being biased with a spring such that it will only open when pressure within the face-piece exceeds that of the surrounding atmosphere by, say, 4 millibar.

It may be seen that during respiration, pressure within the face-piece is maintained at a level that is between 2 and 4 millibar greater than the pressure of the surrounding atmosphere. By this means, should there be a leak in the face-piece or an imperfect seal to the wearer's face, only outward leakage can occur and the ingress of ambient atmosphere is thus prevented.

It is an object of the present invention to provide an improved form of breathing apparatus demand valve.

Summary of the Invention

According to the present invention there is provided a demand valve for breathing apparatus whereby breathable gas, stored under pressure, is admitted to a face-piece, hood or helmet at a rate that matches the respiratory requirements of the wearer whilst at the same time maintaining a super-ambient pressure within the face-piece, the demand valve having a housing with an outlet port for connection to the face-piece and an inlet connection terminating inside the housing with a conical jet, abutting the end face of which is a resilient seating mounted upon a lever affixed to the housing by means of a pivot such that rotation of the lever about the pivot causes the resilient seating to move towards or away from the jet, the free end of the lever being engaged with a hook or bridge attached to a rigid central portion of a flexible pressure-responsive diaphragm, the periphery of which is sealed to the housing such that changes in pressure within the housing will cause the diaphragm to move inwards or outwards, so controlling the position of the lever and thus the position of the resilient seating with respect to the jet, the seating being forced away from the jet by the pressure of the gas at the inlet, such that a super-ambient pressure is required within the housing to move the diaphragm outwards and thus close the seating against the jet, the lever having a projecting vane so positioned as to deflect the flow of incoming gas from the jet away from the diaphragm and towards the outlet port, the deflection of gas also providing an additional opening force to the lever which increases in proportion to the incoming gas flow.

The arrangement is preferably such that the pressure of supply gas at the inlet of the valve biases the valve open such that a super-ambient pressure within the valve housing is required to close off the flow of supply gas into the housing, the supply pressure and the relative proportions of the gas inlet jet, the lever and the diaphragm being so arranged as to provide the required level of said super-ambient pressure.

If required, an additional opening force may be applied to the valve, by means of a spring applied either to the lever or to the diaphragm.

An important feature of the present invention is that the projecting vane on the valve operating lever is so positioned and so proportioned that the flow of gas entering the valve housing from the inlet connection impinges upon the vane and is deflected by it away from the diaphragm and towards the outlet port, the force applied by the incoming gas flow impinging upon the vane also providing an additional opening bias to the valve.

It will be appreciated that the present invention provides a positive pressure demand valve of very simple and robust construction.

Brief Description of the Drawings

Figures 1 and 2 show the valve in its open and closed positions respectively.

Description of the Preferred Embodiment

The demand valve comprises a housing (1) with a cover (2) which has one or more openings or ports (3) to allow access of ambient pressure to a flexible diaphragm (4), the periphery of which is sealed to the housing in an airtight manner. The diaphragm has a rigid central portion (5), on which there is a hook or bridge (6) which engages with the free end of a rigid lever (7), the other end of which is attached to the housing by means of a pivot (8).

A cylindrical inlet connection (9), which terminates at its inner end in a conical jet (10) and at its outer end in a means (11) for attaching a gas supply hose (12), enters the housing through a threaded block (13) adjacent to the lever pivot (8). A resilient seating (14) is secured to the face of the lever (7), adjacent to the pivot (8), such that it faces towards, and is concentric with, the end face of the conical jet (10) and is moved towards or away from the face of the jet by movement of the lever (7) about its pivot (8). The threaded inlet connection (9) is adjusted longitudinally so that, at the point of closure between the face of the seating (14) and the end face of the conical jet (10), the two surfaces will be substantially parallel to one another.

A locknut (15), or other suitable locking means, secures the inlet connection (9) in the correct position.

The lever (7) has a projecting blade or vane (16), the function of which is two-fold and which is described in detail below. An outlet port (17) in the housing connects the demand valve to the face-piece of the breathing apparatus, either by direct attachment to the face-piece itself, via a suitable connecting means, or via a flexible hose.

The demand valve operates in the following manner:-Breathing gas, supplied at a substantially constant pressure via the supply hose (12), enters the inlet connection (9), where it forces the seating (14) away from the face of the conical jet (10), thus rotating the lever (7) about its pivot (8). This, in turn, pulls the diaphragm (4) inwards due to the engagement of the free end of the lever (7) with the bridge in the center of the diaphragm (4). In this condition, gas flows into the housing, from which it passes through the outlet port (17) to the face-piece, where it causes pressure to rise, its escape from the face-piece being regulated by the spring-loaded exhalation valve. This rise in face-piece pressure is communicated, via the outlet port (17), to the diaphragm (4), which is subsequently urged outwards and thus pulls on the free end of the lever (7), rotating it about the pivot (8) and closing the resilient seating (14) against the face of the conical jet (10) to control the inflow of gas from the hose.

It will be seen that the demand valve, according to the present invention, requires no biasing spring in order to maintain a positive pressure within the face-piece, this function being performed by the pressure of the incoming gas alone. The projecting vane (16) on the lever (7) performs two functions, serving to greatly improve the performance of the demand valve. Without the inclusion of the vane (16), a simple demand valve as described above would suffer from three undesirable effects.

Firstly, due to the resilient seating (14) moving through an arc as the valve opens, as defined by the lever pivot (8), gas entering the valve housing from the inlet connection (9) is deflected by the angled seating (14) towards the diaphragm, upon which it impinges. The further the valve opens, the greater will be the flow of gas impinging upon the diaphragm (4) and thus the greater will be the resulting force urging the diaphragm (4) outwards, which, in turn, pulls upon the lever (7) and applies a closing force to the valve. Secondly, the further the valve opens, the lesser will be the force applied to the seating (14) by the pressure of the incoming gas, partly because of the angle between the incoming air stream and the seating (14) and partly due to the fact that the gas expands into the housing as it leaves the jet, so losing pressure and therefore applying less force to the seating (14). Thirdly, any resistance to gas flowing out of the housing to the face-piece, particularly that resistance which would be imposed by including a tube or hose between the demand valve and the face-piece, would result in an increase in pressure within the valve housing with increasing flow, resulting once again in the diaphragm being urged outwards with a force that increases with flow.

It will be seen that the combined result of the effects described above would be a reduction in positive pressure within the face-piece as flow increases, which is contrary to the requirement that the valve should maintain the required positive pressure level within the face-piece regardless of the flow required by the wearer.

The provision of the projecting vane (16) on the lever (7) overcomes the undesirable effects described, in the following manner:-As the valve opens, the incoming gas is deflected towards the diaphragm (4), as previously described. However, the projecting vane (16) deflects the flow of gas, with three advantageous results. Firstly the gas flow does not impinge upon the diaphragm (4) and thus does not urge it outwards. Secondly, the force applied to the vane (16) itself, on which the gas flow now impinges, serves to increase the opening force applied to the lever (7) as the gas flow increases.

Thirdly, the gas flow is deflected by the vane (16) towards the outlet port (17), which further improves the flow of gas out of the valve housing to the face-piece.

Claims

Claims:- 1. A demand valve for breathing apparatus whereby breathable

gas, stored under pressure, is admitted to a face-piece, hood or helmet at a rate which matches the respiratory requirements of the wearer whilst at the same time maintaining a super-ambient pressure within the face-piece, the demand valve having a housing with an outlet port for connection to the face-piece and an inlet connection terminating inside the housing with a conical jet, abutting the end face of which is a resilient seating mounted upon a lever affixed to the housing by means of a pivot such that rotation of the lever about the pivot causes the resilient seating to move towards or away from the jet, the free end of the lever being engaged with a hook or bridge attached to the rigid central portion of a flexible pressure-responsive diaphragm, the periphery of which is sealed to the housing such that changes in pressure within the housing will cause the diaphragm to move inwards or outwards, so controlling the position of the lever and thus the position of the resilient seating with respect to the jet, the seating being forced away from the jet by the pressure of the gas at the inlet, such that a super-ambient pressure is required within the housing to move the diaphragm outwards and thus close the seating against the jet, the lever having a projecting vane so positioned as to deflect the flow of incoming gas from the jet away from the diaphragm and towards the outlet port, the deflection of gas also providing an additional opening force to the lever which increases in proportion to the incoming gas flow.

2. A demand valve for breathing apparatus as claimed in Claim 1, wherein the arrangement is such that the pressure of supply gas at the inlet of the valve biases the valve open such that a super-ambient pressure within the valve housing is required to close off the flow of supply gas into the housing.

3. A demand valve for breathing apparatus as claimed in Claim 2, in which the supply pressure and the relative proportions of the gas inlet jet, the lever and the diaphragm are so arranged as to provide the required level of said super-ambient pressure.

4. A demand valve for breathing apparatus as claimed in any one of the preceding claims, which includes a spring that applies an additional opening force to the valve, said spring being applied either to the lever or to the diaphragm.

5. A demand valve for breathing apparatus as claimed in any one of the preceding claims, wherein the projecting vane on the valve operating lever is so positioned and so proportioned that the flow of gas entering the valve housing from the inlet connection impinges upon the vane and is deflected by it away from the diaphragm and towards the outlet port, the force applied by the incoming gas flow impinging upon the vane also providing an additional opening bias to the valve.

6. A demand valve for breathing apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

7. Breathing apparatus that includes a demand valve as claimed in any one of the preceding claims.