GB1570065A

GB1570065A - Breathing apparatus

Info

Publication number: GB1570065A
Application number: GB4391775A
Authority: GB
Original assignee: DRAEGER SAFETY Ltd
Current assignee: DRAEGER SAFETY Ltd
Priority date: 1976-10-21
Filing date: 1976-10-21
Publication date: 1980-06-25

Description

(54) IMPROVEMENTS RELATING TO BREATHING APPARATUS (71) We, DRAEGER SAFETY LIM ITED, a British Company, of Kitty Brewster, Blyth, Northumberland, NE24 4RH, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns breathing apparatus and is especially concerned with breathing apparatus for use by firemen, mine rescue personnel and the like, when operating in a noxious or hazardous atmosphere. The invention is, however, also applicable to breathing apparatus for use by airmen.

The invention is especially applicable to breathing apparatus of the type (herein called "the type defined") including a so-called demand regulator that controls the delivery of a breathable gas to a mouthpiece, oronasal mask or helmet in accordance with the natural respiration of the user, the regulator responding to the pressure drop caused by the commencement of inhalation by the user to open a valve controlling the supply of breathable gas. The demand regulator may take various forms and one such form that has been used most successfully is disclosed in U.K. Patent Specification 775314.

Typically the demand regulator of a breathing apparatus of the aforesaid type is supplied with breathable gas - e.g. oxygen or compressed air - under a pressure of about 115 psig from a suitable source that may, for instance, be a pressure regulator connected to a high-pressure compressed gas reservoir. In the conventional operating mode the demand regulator cuts off the supply of breathable gas until a pressure below ambient appears on the downstream side of the regulator as a result of the commencement of inhalation by the user.

In the use of such breathing apparatus in certain noxious or hazardous atmospheres it is important to avoid any leakage of the ambient atmosphere into the gas breathed by the user.

This demands very efficient sealing between an oronasal mask and the face of the user or equivalent efficient sealing in the case of a helmet in order that the negative pressure induced at the commencement of each inhalation period and that may persist for a substantial part of the duration of an inhalation period shall not cause inward leakage of the ambient atmosphere into the mask or helmet as the case might be.

A similar requirement arises in the case of breathing apparatus for airmen and intended to deliver air-diluted oxygen in at least one operating mode, for instance, over a range of operating altitudes: in such an operating mode any inward leakage of the ambient atmosphere can cause over-dilution of the oxygen delivered to the airman and diminution in the total amount of oxygen inhaled, leading possibly to oxygen starvation.

There is also the danger that the user, having to provide the motive power to operate the demand regulator to release breathable gas during each inhalation, will tend to inhale more deeply than necessary and so over-satisfy his breathable gas requirements and inadvertently induce a state of hyperthermia.

In the case of airmen's breathing apparatus it is now common to arrange that the demand regulator delivers breathable gas under a small positive pressure relative to ambient when operating in a mode in which inward leakage of ambient atmosphere would be hazardous for the reasons explained. Similarly, breathing apparatus for firemen and other rescue personnel is now required to deliver breathable gas in such manner that negative pressure, relative to ambient, cannot occur within the conduits, mask, helmet and so on, conveying the breathable gas from the demand regulator to the respiratory system of the user, the current requirement for officially approved breathing apparatus being that a specified minimum positive pressure shall be maintained or exceeded at all times within conduits and components so that any leakage is of breathable gas outwardly to the atmosphere.

A specific object of the present invention is to provide a demand regulator capable of meet ing this requirement in a particularly effective manner.

In accordance with the present invention we provide a demand regulator for breathing apparatus of the type defined, such demand regulator comprising a valve for controlling the supply of breathable gas from a pressure source to a user outlet; and valve-operating means including means sensitive to the differential between ambient pressure and pressure downstram of said valve and adapted to open the valve in response to falling pressure downstream of the valve, and spring biassing means arranged, in an operative position, to assist the valve-open ing effort of said differential-sensitive means in response to falling pressure downstream of the valve so that the latter is opened whenever cthe pressure downstream thereof has less than a prescribed excess over ambient pressure, the spring biassing means being arranged to be capable of being overridden, in either sense, temporarily by deliberate action by a user.

When the spring biassing means is located in said operative position, the demand regulator is arranged to deliver breathable gas to the user outlet under an appropriate positive pressure relative to ambient. The spring biassing means can, however, be overridden in either sense, if desired, for example to meet special requirements. Thus, by overriding the spring biassing in one sense, positive opening of the valve can be effected and the valve held open for the purpose, for example, of purging components connected to the user outlet with breathable gas.Alternatively, by overriding the spring biassing means in the opposite sense, the differ ential-sensitive means can be relieved of the effect of the spring biassing means so that the valve will remain closed with zero pressure differential across said differential-sensitive means, for the purpose, for instance, of testing the valve for leakage.

Preferably said valve is a tilt valve comprising a member urged against an annular seat and openable by rocking of the valve member upon such seat. The tilt valve member may be urged upon a downstream seat by upstream pressure, alone or with spring assistance, or the valve member may be spring-pressed against an upstream seat. In the former case a by-pass and pressure relief valve may be provided to vent excess upstream pressure as described in U.K. Specification No. 1,367,286, whereas in the latter case the arrangement may be self relieving in the event of excess upstream pressure.

The valve operating means may conveniently comprise a diaphragm having one face exposed to ambient and its other exposed to pressure downstream of the valve and adapted to deflect in response to the pressure differential there across so as to open the valve at appropriate differential pressure values.

When the valve-operating means comprises a diaphragm as aforesaid, the spring biassing means conveniently comprises a compression spring acting on the same face of the diaphragm as ambient pressure. In this case, the spring preferably acts on a plunger movable by a user in opposite senses to override the action of the spring when required. The plunger is desirably movable to a latched condition relieving the diaphragm of the thrust of the spring, thereby to enable the valve to remain closed with zero pressure differential across the diaphragm.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: FIGURE 1 is a vertical section through a demand regulator embodying the invention; FIGURE 2 is a front elevation of a cover sub-assembly of the demand regulator of Figure 1, a cap thereof being omitted for clarity; FIGURE 3 is a section on the line X-X of Figure 2; and FIGURE 4 is a part-sectional view of a detail of the cover sub-assembly in the direction X-X' in Figure 2.

The illustrated demand regulator comprises a body 1 having an outlet connection 2 and an inlet port 3 that communicates with a tilt valve assembly generally designated 4. The assembly 4 comprises a body providing an annular valve seat 5 encircling the upstream end of an inlet passage 6 and engaged by a valve member 7 that is urged against the seat 5 by upstream pressure acting on the member 7. The valve member 7 has a stem 8 that extends through the inlet port 3 and into the body 1 and carries a deflector 9 that serves to interfere with the flow of a gas along the stem 8 when the valve is open and causes the gas to be deflected to the outlet connection 2.

Because excess upstream pressure may clamp the valve member 7 on its seat 5, a bypass arrangement as disclosed in U.K.

Specification No. 1,367,286 is provided, this comprising an annular seat 10 surrounding the downstream end of the inlet passage 6 and cooperating with an annular relief valve 11 urged against the seat 10 by a spring 12. A passage 13 extends between the upstream and downstream ends of the inler passage-detining part of the body of the valve assembly 4, outboard of the seats 5 and 10. Excess upstream pressure can thus unseat the relief valve 11 and allow a flow through the passage 13.

The body 1 has a cover 14 that is secured to the periphery of the body 1 by means of a V-band clamp 15 with tightening screw 15a.

The body is spanned by a diaphragm having a flexible peripheral portion 16 damped between the body 1 and the cover 14, and a rigid disc 17 having a thickened central region 18 formed with a nib 19 that engages the extremity of the stem 8 of the tilt valve assembly.

The cover 14 is apertured so that the adjacent side of the diaphragm is exposed to ambient atmospheric pressure while the other side of the diaphragm is, of course, exposed to the pressure within the body 1 downstream of the tilt valve assembly 4. The arrangement is such that movement of the diaphragm in response to falling pressure within the body causes the stem 8 to be rocked to unseat the valve member 7 and so enable gas to flow through the inlet passage 6 to the inlet port 3 and thus to the outlet connection 2. When the diaphragm is in the position shown in Figure 1, the valve member 7 is seated to prevent such flow of gas through the valve assembly 4.

In accordance with the invention the diaphragm is subject to spring biassing that assists the ambient atmospheric pressure to move the diaphragm in the sense required to accomplish unseating of the valve member 7. Thus the cover 14 carries a central sleeve 20 that provides a guide for a plunger 21 screwed onto a threaded axial spindle 22 and secured thereto by a pair of grip screws 23 in radial bores in the plunger and extending opposed grooves 24 in the spindle 22. The spindle 22 has a head 25 positioned to engage the centre of the thickened central region 18 of the diaphragm. An external cap 26 is screwed onto the free end of the spindle 22 and secured thereto, in the same manner as the plunger 21, by a pair of grub screws 27.The spindle 22 also carries a thrust disc 28 and a coil spring 29 operates between the thrust disc 28 and the sleeve 20 to urge the spindle towards the diaphragm.

The spring-biassing system is shown in a withdrawn position in which the head 25 of the spindle 22 is kept clear of the diaphragm by the heads 30 of a pair of screws 31 resting upon chamfered cam rests 32 of the sleeve 20, the screws 31 extending into the plunger 21 perpendicular to and axially offset with respect to the screws 23. For normal operation, the cap 26 is pulled and turned to an operative position in which the screw heads 30 are disposed adjacent a pair of semi-cylindrical grooves 33 provided in the inner surface of the sleeve 20.

In this position, the cap 26 and attached spindle 22 and plunger 21 are free to move towards the diaphragm under the force of the spring 29, the screw heads 30 sliding in the grooves 33, and the head 25 of the spindle 22 is thus urged into engagement with the centre of the diaphragm to apply thrust to the latter, tending to move this in the direction to unseat the valve member 7.

In operation of the illustrated demand regulator, a source of breathable gas such as compressed air is connected to the upstream or inlet end of the tilt valve assembly 4 and typically is arranged to supply the breathable gas at a regulated pressure of 115 + 15 psig.

With the diaphragm in the position shown in Figure 1, this normal upstream pressure acting on the valve member 7 provides sufficient thrust to hold the valve member 7 sealingly engaged with the seat 5 but allows the member 7 to be tilted on its seat in response to lateral loads on the stem 8 by the diaphragm in response to inhalation by the user. However, in the event of a pressure regulator failure or other circumstance leading to a significant increase in pressure upstream of the valve member 7 (for instance to a pressure of about 160 psig) the thrust on the member 7 could prevent this being tilted but under such pressure the spring 12 permits the relief valve 11 to unseat to provide breathable gas for inhalation when required, excess released gas exhausting through the expiration valve (not shown) of the breathing apparatus with which the demand regulator is associated.

While the spring 29 acts to load the diaphragm, the latter can only attain the position shown in Figure 1, in which the valve member 7 is seated to prevent flow of gas through valve assembly 4, when the pressure within the body 1 exceeds the ambient atmospheric pressure by a value determined by the thrust of the spring 29. Accordingly, whenever pressure within the body 1 exceeds ambient atmospheric pressure by less than this limiting pressure difference, the spring 29 urges the diaphragm towards the left, as seen in Figure 1, and causes the tilt valve assembly 4 to open to admit breathable gas to the body and so restore the required minimum pressure difference between the breathable gas in the body 1 and the ambient atmospheric pressure.

During normal operation of the illustrated demand valve, respiration by the user is accomplished by corresponding movement of the diaphragm to open and close the tilt valve assembly to supply breathable gas at the rate demanded by the user while maintaining in the breathing apparatus components connected to the outlet connection 2 a pressure that is always positive with respect to the ambient atmosphere, it being understood that the breathing apparatus -- e.g. the facemask or helmet connected to the outlet connection 2, is provided with an expiration valve that unseats to permit the escape of gas when the pressure exceeds ambient atmospheric pressure by an amount suitably greater than the pressure sought to be maintained in the said component by the operation of the demand valve.

As the diaphragm deflects in consequence of the respiration of the user, the plunger 21 and cap 26 will oscillate in synchronism giving a visible indication of the functioning of the regulator. However, the operation of the plunger may be interfered with by the user and may, for instance, be deliberately held out against the thrust of the spring 29, manually or by being latched in the position shown in the drawings, so as to unload the diaphragm for the purpose of testing the tilt valve assembly for leakage and pressure holding before the breathing apparatus is donned - or to prevent loss of breathable gas during temporary removal of a facemask or helmet.In the latched condition shown, the thrust of the spring is resisted by engagement of the screw heads 30 with the cam rests 32 on the rear end of the sleeve 20, a condition attained by pulling the cap 26 outwardly and rotating it to move the screw heads 30 out of alignment with the grooves 33. On the other hand, inwards movement of the plunger 21 by manual thrust on the cap 26 may be utilized to effect positive opening of the tilt valve assembly irrespective of the pressure within the body 1 for the purpose, for instance, of rushing the body and components connected thereto with breathable gas.

WHAT WE CLAIM IS:- 1. A demand regulator for breathing apparatus of the type defined, such demand regulator comprising a valve for controlling the supply of breathable gas from a pressure source to a user outlet; and valve-operating means including means sensitive to the differential between ambient pressure and pressure downstream of said valve and adapted to open the valve in response to falling pressure downstream of the valve, and spring biassing means arranged, in an operative position, to assist the valve-opening effort of said differential-sensitive means in response to failing pressure downstream of the valve so that the latter is opened whenever the pressure downstream thereof has less than a prescribed excess over ambient pressure the spring biassing means being arranged to be capable of being overridden, in either sense, temporarily by deliberate action by a user.

2. A demand regulator according to claim 1, wherein said valve is a tilt valve comprising a valve member urged against an annular seat and openable by rocking of the valve member upon such seat.

3. A demand regulator according to claim 2, wherein the tilt valve member is urged upon a downstream seat by upstream pressure.

4. A demand regulator according to claim 3, including a by-pass for the tilt valve and a pressure relief valve to vent excess pressure upstream of the tilt valve.

5. A demand regulator according to any one of the preceding claims, wherein the valveoperating means comprises a diaphragm having one face exposed to ambient and its other face exposed to pressure downstream of the valve and adapted to deflect in response to the pressure differential thereacross so as to open the valve at appropriate differential pressure values.

6. A demand regulator according to claim 5, wherein the spring biassing means comprises a compression spring acting on the same face of the diaphragm as ambient pressure.

7. A demand regulator according to claim 6, wherein said compression spring acts on a plunger movable by a user in opposite senses to override the action of the spring on the diaphragm.

8. A demand regulator according to claim 7, wherein said plunger is movable to a latched condition relieving the said diaphragm of the thrust of said spring.

9. A demand regulator substantially as described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. resisted by engagement of the screw heads 30 with the cam rests 32 on the rear end of the sleeve 20, a condition attained by pulling the cap 26 outwardly and rotating it to move the screw heads 30 out of alignment with the grooves 33. On the other hand, inwards movement of the plunger 21 by manual thrust on the cap 26 may be utilized to effect positive opening of the tilt valve assembly irrespective of the pressure within the body 1 for the purpose, for instance, of rushing the body and components connected thereto with breathable gas. WHAT WE CLAIM IS:-

1. A demand regulator for breathing apparatus of the type defined, such demand regulator comprising a valve for controlling the supply of breathable gas from a pressure source to a user outlet; and valve-operating means including means sensitive to the differential between ambient pressure and pressure downstream of said valve and adapted to open the valve in response to falling pressure downstream of the valve, and spring biassing means arranged, in an operative position, to assist the valve-opening effort of said differential-sensitive means in response to failing pressure downstream of the valve so that the latter is opened whenever the pressure downstream thereof has less than a prescribed excess over ambient pressure the spring biassing means being arranged to be capable of being overridden, in either sense, temporarily by deliberate action by a user.