Abstract:
There is described a demand valve for a breathing apparatus wherein a pilot jet of the demand valve is controlled by a pivoting lever resiliently held against a planar face in which the pilot jet is formed. The pilot jet is preferably formed in a land surface surrounded by a recessed area of the planar face, and opening of the pilot jet is effected by movement of a control projection mounted on the pivoting lever. The area of the control projection is preferably greater than the area of the land surface. A bypass arrangement for a demand valve is also disclosed

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to demand valves for breathing apparatus whereby breathable gas stored under pressure is supplied to a face-piece, hood or helmet at a rate according to the respiratory requirements of the wearer, whilst at the same time maintaining a predetermined pressure within the face-piece, hood or helmet. The predetermined pressure is set either as super-ambient, or positive, so as to prevent any inward leakage of ambient atmosphere, or may be set as a negative pressure so that gas is only supplied when the wearer inhales. 
     Positive pressure demand valves for breathing apparatus are well known and employ a variety of mechanisms to control the flow of gas to the wearer according to his requirements, such mechanisms being actuated by movement of a pressure responsive diaphragm exposed on one side to ambient pressure and on the other side to pressure within the face-piece such that, when the wearer inhales, causing a drop in pressure within the face-piece, the diaphragm moves inwards, actuating the valve mechanism to admit gas to the face-piece at a rate proportional to the pressure drop. When inhalation ceases, equilibrium is restored and the valve closes. In order to maintain a small positive pressure within the face-piece, the valve is biased open, typically by means of a spring bearing against the outer face of the diaphragm such that a pressure of, say, 2 millibar within the face-piece is required to move the diaphragm outwards against the spring and thus close the valve. The wearer&#39;s exhaled breath is vented from the face-piece to the surrounding atmosphere through a simple non-return valve which is biased closed with a spring so as to only open when pressure within the face-piece exceeds ambient pressure by, say, 4 millibar. Thus it may be seen that pressure within the face-piece is continuously maintained at a level of between, say, 2 and 4 millibar above that of the surrounding atmosphere and by this means, any leakage due to damage or imperfect sealing of the face-piece, can only be outwards, so preventing any ingress of ambient atmosphere to the face-piece. 
     SUMMARY OF THE INVENTION 
     For many applications, it is required to provide the demand valve with a manually operated bypass valve in order to supply a controlled continuous flow of breathable gas to the wearer independently of the normal demand operation. 
     An objective of the present invention is to provide a demand valve of simplified construction and assembly, wherein accurate positioning of moving parts is achieved with the minimum number of components. 
     A further objective of the present invention is to provide a two-stage demand valve whose performance is reliable and predictable, but which requires a minimum of precision-made components 
     A further objective of the present invention is to provide a manual bypass arrangement for use in demand valves, incorporating a simplified construction with a minimum number of components, which provides to a wearer of the demand valve the possibility of a continuous flow of breathable gas to the facepiece. 
     One aspect of the present invention provides a pilot operated demand valve which is efficient, reliable and predictable in operation and is of small physical size and simple construction. A second aspect of the invention provides a bypass arrangement for a demand valve. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which; 
     FIG. 1 shows a sectional elevation of the valve in its closed condition; 
     FIG. 2 shows a sectional elevation of the valve in its open condition; 
     FIG. 3 shows a plan view of the valve showing an operating lever and its retaining wire form; 
     FIGS. 4 a ,  4   b  and  4   c  show top, side and underneath views of the lever respectively; 
     FIG. 5 shows a sectional view of the valve with a bypass valve included; and 
     FIG. 6 shows a section of the bypass valve plug. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures, the valve comprises a circular, generally disc-like body  1  having a radially extending inlet bore  6  and an axially extending outlet port  17  opening to one face of the disc-like body  1  and communicating with the inlet bore  6 . The outlet port  17  opens into a recess  18  divided by an annular rib  50  into a central part  51  and an annular surrounding part  24 . The outlet port  17  is surrounded by the annular rib  50 . 
     Extending parallel to, and in communication with, the inlet bore  6  is a pilot bore  5 . A pilot jet  4  extends from the pilot bore  5  to the other face  2  of the disc-like body  1 . The face  2  of the body is made flat, and is formed with an annular recess  3  surrounding the jet  4 , the end face of the jet  4  being set level with face  2 . 
     Extending into the inlet bore  6 , to its radially inner end, is a tubular inlet stem  7  which is rotatable within the bore  6  and which is formed at its radially outer end with a barbed stem  8  serving as a connection means for a supply hose (not shown). An annular seal  9  is housed in a groove around the inlet stem  7  to seal the stem  7  against the wall of the inlet bore  6  adjacent the radially outer end of the inlet bore  6 . Close to the radially inner end of the stem  7 , the stem  7  has an area of reduced diameter  10 , which forms an annular chamber with the inlet bore  6  and defines a flange  11  at the end of the stem. Extending through the flange  11  in the axial direction of the stem are a number of openings  12  which provide fluid communication between the end face of the inlet stem  7  and the annular chamber area. 
     Adjacent to the end face of the inlet stem  7  there is a resilient valve disc  13 , the periphery of which seals against the wall of the inlet bore  6 . The centre of the valve disc is penetrated by a small metering orifice  14 . The area of the valve disc between the metering orifice  14  and the periphery of the disc seals the openings  12  in the flange  11  of the inlet stem  7 . 
     Between the valve disc and the radially inner end face of the inlet bore  6 , there may be interposed a dished supporting disc  15 , concave towards the stem  7 , which forms a conical or domed chamber  16  between the valve disc  13  and the end face of the inlet bore  6 . This chamber is in communication with the pilot bore  5  and the jet  4 , by means of channels in the supporting disc  15 . Alternatively, the end of the inlet bore  6  may be made concave so as to form the domed chamber  16 , as is shown in FIG.  2 . 
     The outlet port  17  in the body communicates between the annular chamber  10  and a recess  18  which houses a pair of wire screens  19  and  20 , which are spaced apart and secured within the recess  18  by means of tightly fitting rings  21  and  22 . The screen  19  rests against the end of the annular rib  50 , while the screen  20  is spaced from the screen  19  by the ring  21 . The rib  50  prevents direct fluid communication between the outlet port  17  and the annular space  24  between the screen  19  and the body  1  outside the annular rib  50 . One end of a passage  23  extending through the body opens into this annular space  24  between the first screen  19  and the body  1 , and the other end of the passage  23  opens on the face  2  of the body  1 . The valve body  1  is adapted, by means of a groove  25  or by other suitable attachment means surrounding the recess  18 , such as a screw thread or a bayonet fitting, to connect in a leak tight manner to a corresponding attachment means on a face-piece of a breathing apparatus or to a hood. 
     A lever  26  is arranged to extend radially across the face  2  of the valve body  1 . The lever  26  has two projections  27  intermediate the length of the lever which engage face  2  of the body  1 , and a control projection  28  which is positioned at a first end of the lever over the jet  4 , and has a flat face to contact the face  2  of the body  1 . A second end of the lever is positioned substantially centrally with relation to the body  1 , and is spaced from the flat face  2  of the body  1 . 
     The lever  26  is held in this position by means of a generally U-shaped spring wire form  29 , whose central section is located in a transverse groove  30  extending across the lever between the projections  27  and the control projection  28 . The “legs” of the U-shape extend longitudinally of the lever, with the ends of the spring wire form secured in holes  31  formed in the face  2  of the body. The spring wire form  29  exerts a force on the lever urging it in the direction of the face  2 . A ridge or embossment  32  positioned centrally in the groove in the lever and upon which the wire form bears, ensures that the force applied by the wire form is substantially evenly applied to the two projections  27  upon which the lever stands, even if that part of the wire form which passes through the groove is not parallel to surface  2 . 
     The groove  30  in the lever is preferably positioned nearer to the control projection  28  than to the projections  27 , so that the force of the spring wire  29  is mainly applied to the control projection  28 . In the most preferred position, the groove  30  is spaced twice as far from the projections  27  as it is from the control projection  28 . The groove must be positioned so that the force exerted on the projection  28  by the wire form  29  can overcome the supply pressure of gas at the jet  4 . 
     The lever  26  is so shaped that it can be tilted to a limited degree by moving the second end of the lever towards the face  2  of the body, rocking the lever about an axis defined by the engagement of the two projections  27  with face  2 . When the lever  26  is so tilted, the control projection  28  will move away from the jet  4 . 
     The lever  26  is positioned between the face  2  of the body  1  and a flexible diaphragm  33 , having a rigid central plate  34  and a peripheral bead  35  shaped to fit into and seal against the faces of a groove formed in an upstanding rim projecting from the face  2 . The diaphragm  33  and the face  2  define a variable volume into which the jet  4  and the passage  23  open. 
     The diaphragm  33  is held in contact with the second end of the lever  26  by means of a biasing spring  36 , one end of which is in contact with the face of the diaphragm  33  remote from the body  1 , and the other end of which is retained in a recess in an adjusting screw  37  threaded into a central boss in a rigid cover  38  attached to the body  1  and covering the diaphragm  33 . A small hole  39  in the adjusting screw  37  admits ambient pressure to the outer face of the diaphragm  33 . In an alternative embodiment (not shown) a vent hole may be formed in the cover  38  to provide fluid communication between the ambient atmosphere and the face of the diaphragm  33  remote from the body  1 . 
     In a positive-pressure demand valve, arranged to prevent any inward leakage of ambient atmosphere into the facepiece, the pressure exerted on the diaphragm  33  by the adjusting spring  36  is adjusted so that, in the absence of a pressurised gas supply to the demand valve, the second end of lever  26  is held in contact with face  2  of the valve body, and the jet  4  is open. 
     The cover  38  has a substantially circular central portion to cover the diaphragm  33 , and a depending peripheral flange to engage the periphery of the body  1 . The peripheral flange has an arched cut-out  40  which engages with a groove or step  41  around the inlet stem  7  so as to prevent the inlet stem  7  from moving out of the inlet bore  6  of the body  1 , and to allow the stem  7  to rotate. The cover  28  is secured to the body  1  by screws  42  extending through the flange. Alternative fixing means may be used, however. 
     In operation, a breathable gas is supplied to the demand valve from a supply hose at a pressure of about 10 bar, and passes through the central bore in the tubular inlet stem  7 . The pressure of the gas deforms the resilient valve disc  13  into a domed shape, moving the valve disc away from the end face of the inlet stem  7  and allowing gas to pass through the openings  12  in flange  11  to the annular chamber  10 , from which it passes through port  17  to the recess  18  and hence to the face-piece. 
     At the same time, a small continuous flow of gas passes through the metering orifice  14  in the valve disc  13  into the domed chamber  16  behind the disc, from whence it can escape through the bore  5  and the jet  4 , while the lever  26  is held in a tilted position by the biasing spring  36  bearing against the diaphragm  33 , such that the control projection  28  on the lever is held away from the jet  4 . The small flow of gas from the jet  4  escapes freely from the space under the diaphragm through passage  23  to the annular space  24  and thence through the screens  19  and  20 . 
     When the facepiece is sealed to the face of a wearer, the flow of gas from the valve outlet inflates the facepiece, causing the pressure within the face-piece to rise. Escape of gas from within the facepiece is controlled by a spring loaded exhalation valve. The pressure increase is communicated via passage  23  to the space between the diaphragm  33  and the face  2 . The pressure acts upon the diaphragm  33 , urging it away from the body  1  against the force of the biasing spring  36 . This allows the lever  26  to be moved under the influence of the spring wire form  29  to bring the control projection  28  into contact with the face  2 , closing the jet  4 . 
     When the jet  4  is obstructed by the control projection  28  of the lever  26 , the egress of gas through the jet  4  from the domed chamber  16  is interrupted, and the pressure in the domed chamber  16  rises to equal the pressure of the supplied gas, due to the continuous inflow of gas to the domed chamber through the metering orifice  14  in the resilient valve disc  13 . The increased pressure in the domed chamber  16  urges the resilient valve disc  13  against the flange  11  on the inlet stem  7 , thus closing the openings  12  in the flange and preventing further flow of gas to the outlet  10 . The flow of gas is prevented for as long as the pressure in the facepiece and under the diaphragm  33  is sufficient to overcome the force of the spring  36 . 
     An increase in pressure in the facepiece, such as when the wearer exhales, increases the pressure under the diaphragm  33 , and keeps the jet  4  closed. The facepiece is provided with an exhalation valve which opens when the pressure within the facepiece is at a predetermined level above the ambient pressure, to release used gas. The exhalation valve is preferably arranged to open only when the pressure within the facepiece is sufficient to close the jet  4  of the demand valve. 
     A subsequent reduction in pressure within the face-piece, such as when the wearer inhales, will cause the diaphragm  33  to move towards the body  1  under the influence of the biasing spring  36 , thus tilting the lever to move the control projection  28  away from the jet  4 . Gas can then escape from the domed chamber  16  through the jet  4 , and the pressure in the domed chamber falls such that the valve disc will be urged away from the face of flange  11  by the pressure of the incoming gas, allowing a flow of gas through the openings  12  to the outlet and hence to the face-piece. 
     In a negative-pressure demand valve, arranged to admit gas only when the wearer inhales, the pressure exerted on the diaphragm  33  by the adjusting spring  36  is so set that, in the absence of a pressurized gas supply, the second end of lever  26  is held away from face  2  of the valve body by the wire form  29  and the jet  4  is closed. 
     In operation of the negative-pressure demand valve, a breathable gas is supplied to the demand valve from a supply hose at a pressure of about 10 bar, and passes through the central bore in the tubular inlet stem  7 . 
     Since the jet  4  is obstructed by the control projection  28  of the lever  26 , the egress of gas through the jet  4  from the domed chamber  16  is prevented, and the pressure in the domed chamber  16  rises to equal the pressure of the supplied gas, due to the continuous inflow of gas to the domed chamber through the metering orifice  14  in the resilient valve disc  13 . The increased pressure in the domed chamber  16  urges the resilient valve disc  13  against the flange  11  on the inlet stem  7 , thus closing the openings  12  in the flange and preventing gas from flowing to the outlet  10 . 
     When the wearer inhales, the diaphragm  33  moves towards the body  1  under the influence of the ambient pressure on the outside of the diaphragm  33  and the force of biasing spring  36 , thus tilting the lever to move the control projection  28  away from the jet  4 . Gas can then escape from the domed chamber  16  through the jet  4 , and the pressure in the domed chamber falls such that the valve disc will be urged away from the face of flange  11  by the pressure of the incoming gas, allowing a flow of gas through the openings  12  to the outlet and hence to the face-piece. 
     When the inhalation stops, the incoming gas to the face piece will inflate the face piece and urge diaphragm  33  away from face  2 , thus closing the jet  4  and stopping the further supply of gas. 
     Exhalation by the wearer urges the diaphragm  33  further from face  2 , keeping jet  4  and the gas supply closed. The facepiece exhaust valve vents exhaled air to atmosphere. 
     At the next inhalation, the reduction of pressure within the facepiece caused by the wearer&#39;s intake of breath again causes the jet  4  and demand valve to open, supplying more gas. 
     The outlet screens  19  and  20  serve to diffuse the flow of gas out of the valve and also to provide a pressure feedback via passage  23  to the space under the diaphragm. 
     For the valve to be accurately calibrated to close the openings  12  at a predetermined overpressure within the facepiece, the flow through the jet  4  has to be accurately controllable and predictable. 
     If the jet  4  is formed in the flat face  2  and is closed by a control projection  28  whose diameter is similar to that of the jet  4 , then any eccentricity between the jet  4  and the projection  28  will provide a radial leakage path of low flow resistance as the projection  28  moves off the surface  2 , and this will affect the rate of exit of gas from the jet  4  as the projection  28  moves away from the jet. Extreme accuracy in positioning the projection  28  concentrically over the jet  4  will therefore need to be achieved to provide a uniform response from one valve to the next, and this requires expensive machining of close tolerances to the components. 
     The present invention avoids expensive precision components by providing an annular recess surrounding the jet  4  to define a circular land area of known dimensions surrounding the jet  4 . The control projection  28  of the lever  26  is arranged to be larger than this land area, and is positioned so as completely to cover the land area when urged onto the face  2  by the spring wire  29 . The throttling effect produced as the jet is opened is thus repeatable in production valves, since the radial paths for the gas from the jet  4  between the projection  28  and the land area are all of the same length, even if the projection  28  extends beyond the land area by different amounts in different radial directions. 
     By making the area of projection  28  significantly larger than the land area surrounding the jet  4 , accurate positioning of the projection  28  over the jet is not needed to ensure that the land area is completely covered by the projection  28 . 
     Additionally, the land area surrounding the jet  4  is formed so as to be coplanar with the surfaces which support the projections  27  of the lever, so that movement of the control projection  28  in the initial stages of the movement of the lever  26  is a substantially perpendicular to the plane of the land area surrounding the jet  4 . This “vertical lift” of the control projection  28  off the jet  4  produces a predictable and repeatable venting of the domed chamber  16  through the jet  4  as the lever  26  is tilted. 
     The face  2  of the body  1  is described above as being a planar surface. In order to achieve the advantages of the present invention, and to avoid excessive machining costs, the body  1  may be provided with a land area surrounding the jet  4  and bounded by a recess, and a further area coplanar with the land area for engagement of the projections  27  of the lever  26 . This further area need not entirely surround the recess, and need not be contiguous with the recess, provided that the further area is coplanar with the land area. To ensure this coplanar relationship, the land area and the further area may be formed in a final lapping or other finishing operation on the valve body  1 . 
     As an alternative to mounting the ends of the resilient wire form  29  in openings formed in the face  2 , the spring wires may simply be clamped to the body by a screw clamp arrangement (not illustrated). In a further alternative, the resilient wire may be replaced by a leaf spring. 
     As an alternative to the two projections  27  intermediate the length of the lever which engage the face  2  of the body  1 , the lever may comprise a single elongated ridge extending substantially tangentially to said control projection and spaced therefrom. 
     A second embodiment of a demand valve according to the invention incorporates a manually operated bypass valve and is here described with particular reference to FIGS. 5 and 6. In this valve, the inlet stem  7  is provided with a second annular seal  43  between the annular seal  9  and the annular space  10 , the area between this second seal  43  and the first seal  9  having a reduced diameter so as to define an annular clearance  44  between the inlet stem  7  and the wall of the inlet bore  6 . A cross hole  45  in the inlet stem  7  communicates between the annular clearance  44  and the axial bore of the inlet stem, to provide gas at supply pressure to the annular clearance  44 . 
     A port  46  communicates between the annular clearance  44  and a second radial bore  47  in the body. The radially inner end of the second radial bore  47  communicates with the annular chamber  10  via a small port  59 . 
     A cylindrical plug  48  terminating at its outer end in a knob  49 , is retained in the radial bore  47  by a second arched cut-out  50  in the cover  38 , which engages with a groove  51  around the plug. The base of this groove (seen in FIG. 6) is formed wit with two flats  51   a  and  51   b , between which is a projection  52 . The flats  51   a  and  51   b  abut respective side surfaces  50   a  and  50   b  of the arched cutout  50  in the cover, to limit rotation of the plug  48  to a quarter of a turn. 
     An annular seal  53  is housed in a groove around the plug  48 , and seals the plug against the radial bore  47 . An eccentric bore  54  in the inner end of the plug houses a spring  55  which bears upon a plunger  56 , urging it against a resilient seal  57  housed in a recess  58  in the body and surrounding the small port  59 . 
     The bypass valve is shown in FIGS. 5 and 6 in its closed position, with flat  51   a  contacting side surface  50   a  of arched cut-out  50 . 
     Gas under pressure passes from the axial bore of the inlet stem  7  through cross hole  45  to the area of annular clearance  44  between the stem  7  and the body  1 , and thence through port  46  into the second radial bore  47 . Its escape through small port  59  is prevented by contact between the spring loaded plunger  56  and resilient seal  57 . 
     When the knob  49  is turned, rotating the plug  48  so that flat  51   b  contacts side surface  50   b  of arched cut-out  50 , the plunger  56  sweeps across the seal  57 , exposing the recess  58 , allowing gas to pass through small port  59  to the valve outlet and hence to the face-piece. The rate of flow through the bypass valve is controlled by the size of the small port  59 . 
     It will be appreciated that operation of the bypass valve does not affect, and is not affected by, the normal demand operation of the valve as previously described.