Diaphragm assembly for the demand regulator of a breathing apparatus
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a diaphragm assembly for the demand regulator of a breathing apparatus, and particularly to an assembly wherein the diaphragm has varying effective area and also serves as the exhaust valve. 
     2. Description of the Prior Art 
     In a typical self-contained underwater breathing apparatus, the regulator includes a first stage that reduces the breathable gas pressure to about 140 psi above ambient, and a second stage that supplies this breathable gas to the diver on demand. Inhalation pressure is sensed by a diaphragm within the second stage that cooperates to open a valve which controls the flow of gas to the diver. 
     A relatively large area diaphragm is required to sense the slight pressure drop at the beginning of inhalation. However, this large effective area becomes a disadvantage if an aspirator is used. As the flow rate of breathable gas to the diver increases, there is increasing aspiration effect. Thus the pressure drop sensed by the diaphragm increases disproportionately to actual demand. If the aspirator were set for maximum aspiration effect at low flow rates, the diaphragm would be sucked into the regulator case when the flow rate increased. As a result, prior art regulators required that the aspiration effect be minimized at low flow rates. This insured stable operation at higher mass flow rates, but had the disadvantage of reduced aspiration at times of low flow rate, such as at the beginning and end of the inhalation cycle. 
     An object of the present invention is to provide a demand regulator for a breathing apparatus having a diaphragm of variable effective area that facilitates the use of maximum aspiration at low mass flow rates. 
     Another shortcoming of prior art regulators is that a separate exhaust valve was provided to permit the escape of exhaled gases. A further object of the present invention is to provide a regulator in which the pressure sensing diaphragm also functions as the exhaust valve. 
     SUMMARY OF THE INVENTION 
     These and other objective are achieved by a demand regulator diaphragm assembly employing a diaphragm that gradually flattens down against a conical platform as the pressure in the regulator inner chamber decreases. The diaphragm thus exhibits a varying effective area. 
     When the diaphragm assembly is used with an aspirator, the aspiration effect can be maximized at low mass flow rates. As the flow rate increases, the sensed pressure drops. However, the diaphragm effective area is reduced, so that there is no tendency for the diaphragm to be displaced excessively. Stable operation results at all flow rates, and at all depths. 
     The periphery of the diaphragm seats on an annular ledge at the rim of the conical platform. During exhalation, the excess pressure within the regulator urges the diaphragm periphery away from the platform, opening a flow path for the exhaust gases. Thus the diaphragm assembly also functions as the exhaust valve for the regulator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of the invention will be made with reference to the accompanying drawings wherein like numerals designate corresponding parts in the several figures. These drawings, unless described as diagrammatic, or unless otherwise indicated, are to scale. 
     FIG. 1 is a pictorial view of an underwater breathing apparatus having a regulator second stage incorporating the inventive diaphragm system. 
     FIG. 2 is a sectional view of the regulator second stage as seen along the line 2--2 of FIG. 1, and showing the diaphragm in the rest position. 
     FIG. 3 is a transverse sectional view like FIG. 2, but with the diaphragm shown in a position for high mass flow of breathable gas through the regulator. 
     FIG. 4 is a fragmentary sectional view of another regulator second stage having an adjustable aspirator. 
     FIG. 5 is a perspective view of the aspirator collar used in the regulator of FIG. 4. 
     FIG. 6 is a perspective view showing a portion of the diaphragm platform used in the embodiments of FIGS. 2 through 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention since the scope of the invention best is defined by the appended claims. 
     Operational characteristics attributed to forms of the invention first described also shall be attributed to forms later described, unless such characteristics obviously are inapplicable or unless specific exception is made. 
     In FIG. 1 there is shown a self-contained underwater breathing apparatus incorporating a demand regulator 10 in accordance with the present invention. The scuba system 9 includes a supply tank 11 containing breathable gas under high pressure. Attached to the tank 11 is a conventional regulator first stage 12 which provides the breathable gas at a reduced pressure, typically 140 psi above ambient, to a conduit 13. The regulator second stage 10 is connected to the other end of the conduit 13 via an inlet port 14, and functions to deliver breathable gas to a diver via a mouthpiece 15 upon inhalation demand. 
     As evident in FIGS. 1, 2 and 6, the body 17 of the regulator 10 includes a truncated cylindrical section 17a that defines an interior chamber 18. A flow control valve 19 is situated within a valve housing 20 which is supported coaxially within the body section 17a. The valve 19 controls the flow of breathable gas from the inlet port 14 to the mouthpiece 15 via an outlet port 21 that communicates with the interior chamber 18. 
     Rigidly attached to the truncated body section 17a is a generally cylindrical housing 17b that contains the inventive diaphragm assembly 22. This diaphragm housing 17b includes a cylindrical outer wall 23 having one or more openings 24 that admit water into the interior region 25 rearward of a diaphragm 26. 
     The diaphragm 26 is of generally circular, concave configuration and is made of a resilient rubber or plastic material. The diaphragm assmebly 22 is not rigidly mounted, but rather &#34;floats&#34; within the housing 17b. The center 26a of the diaphragm 26 is affixed to a cylindrical retainer 27 that is rigidly connected to a shaft 28 which projects into the interior chamber 18 and is linked to the flow control valve 19. 
     An annular ridge or seat 30 is provided integral with the diaphragm housing 17b within the region 25. In the quiescent condition shown in FIG. 2, the diaphragm 26 rests on this annular seat 30. The diameter of the seat 30 typically is between about one-third and one-half of the diameter of the diaphragm 26. 
     During exhalation, the pressure in the chamber 18 exceeds that in the chamber 25. As a result, the exhaled gases cause the outer portion 26b of the diaphragm 26 to deflect rearward, as to the position 26b&#39; shown in phantom in FIG. 2. The exhaled gases then flow through the region 25 and out of the regulator body 17 via the openings 24. 
     Only that portion of the diaphragm 26 having a radius larger than the seat 30 is deflected rearward during exhalation. Rearward movement of the central diaphragm section 26c, having a radius less than the seat 30, is prevented by a rigid disc 31 that is attached to the diaphragm retainer 27 and to the shaft 28 by means of a fitting 32. The diameter of the disc 31 is approximately the same as the annular seat 30, so that during exhalation the disc 31 rests atop the seat 30, separated therefrom by the thickness of the diaphragm 26, as shown in FIG. 2. 
     As evident in FIGS. 2 and 6, a rigid, conical platform 35 is formed in a wall 36 that separates the chamber 18 from the interior of the diaphragm housing 17b. The wall 36 has a central opening 37 that is approximately coaxial with the shaft 28 and has a diameter slightly greater than that of the disc 31. The conical platform 35 is truncated by the opening 37. The outer periphery of the platform 35 has a diameter slightly smaller than the diaphragm 26, and forms a ledge 38 against which the diaphragm rests in the quiescent state. A bead 26d at the outer periphery of the diaphragm 26 overhangs the ledge 38. 
     During inhalation the pressure in the chamber 18 is reduced, causing the diaphragm 26 and the shaft 28 to move in the direction of the arrow 40 (FIG. 3). A linkage 41 translates movement of the shaft 28 into axial displacement of a ball 42 that is constrained within a cylindrical bore 43 within the valve housing 20. Displacement of the ball 42 imparts movement to a valve poppet 44 in a direction that causes opening of the flow-control valve 19. 
     The poppet 44 is generally cylindrical, and includes a reduced diameter section 44a situated within a cylindrical bore 45 that communicates with the inlet port 14 via a channel 46. With this arrangement, the annular space 47 between the poppet section 44a and the wall of the bore 45 contains breathable gas at the inlet pressure. Flow of this gas into the bore 43 is prevented by an O-ring seal 48 received in a groove 49 at the periphery of a flange 44b that is an integral part of the poppet 44. 
     The valve 19 itself includes an annular valve seat 51 having a generally V-shaped cross-section and situated at the open end of the bore 45. Cooperating with the seat 51 is an O-ring 52 mounted in an annular shoulder region 44c of the poppet 44. The O-ring 52 is held within an annular groove 53 by the overlapping edge of a conical section 44d of the poppet 44. The exposed portion of the O-ring 52 abuts against the annular valve seat 51 to close the flow valve 19 as shown in FIG. 2. The poppet 44 is biased to this closed position by means of a spring 55 contained within an annular space 56 within the valve housing 20. 
     During inhalation, displacement of the diaphragm 26 causes movement of the poppet 44 in a direction that carries the shoulder 44c and O-ring closure 52 away from the valve seat 51, as shown in FIG. 3. This permits breathable gas to flow from the inlet region 47 past the annular space between the valve seat 51 and the valve closure 52 into the space 56. From there, the breathable gas flows through an aspirator opening 57 formed in the wall of the valve housing 20 into the outlet port 21. In this manner, breathable gas is supplied to the diver on demand. 
     As breathable gas is supplied via the aspirator opening 57, an aspiration or venturi effect occurs which tends to reduce the pressure in the chamber 18. This in turn causes further motion of the diaphragm 26 and the shaft 28 in the direction of the arrow 40, so as to increase the opening of the valve 19 and hence to increase the flow of breathable gas to the diver via the aspirator opening 57. An aspirator &#34;boost&#34; is achieved. 
     In demand regulators having a conventional diaphragm, the aspirator opening must be positioned so that a low flow rates there is very little aspiration effect, and so that the maximum aspiration boost occurs at high flow rates. If the aspirator opening were set to provide maximum aspiration effect at low flow rates, then at a high flow rate the aspiration effect would be so great that the diaphragm would literally be sucked into the regulator interior chamber, and far too much breathable gas would be supplied to the diver. The regulator may become unstable or inoperative. 
     This severe shortcoming of the prior art is overcome in the present invention by reducing the effective diameter of the diaphragm 26 at high flow rates. The reduced effective diameter results as the diaphragm 26 begins to flatten against the conical platform 35 (FIG. 3) during the inhalation cycle. 
     As a result, the aspirator opening 57 can be positioned to provide maximum aspiration effect at low flow rates. As the flow rate increases, more and more of the diaphragm 26 flattens out against the conical platform 35, thereby decreasing the effective area of the diaphragm exposed to the pressure within the chamber 18. At higher flow rates there is increased aspiration effect, resulting in lower pressure in the chamber 18. However, since only a smaller area of the diaphragm 26 is exposed to this decreased pressure, there will be no excessive diaplacement of the diaphragm, as in the case of prior art regulators. In effect, the amount of aspiration effect is reduced at the higher flow rates, as a result of the lessor effective area of the diaphragm 26. Thus, the diaphragm assembly 22 enables the aspirator opening 57 to be set for maximum aspiration effect at very low flow rates, while insuring that as the flow rate increases the aspiration effect will not become excessive. Very stable operation results, and the increased aspiration effect reduces the breathing effort needed to actuate the regulator 10. 
     In the alternative embodiment of FIG. 4, the regulator 10&#39; has an adjustable aspirator. This embodiment is particularly useful for deep-diving applications, where under heavy work conditions a diver may wish to increase the aspiration effect so as to reduce further the breathing effort. In the regulator 10&#39;, this aspirator adjustment can be made externally to the regulator body 17&#39; by slightly rotating the knurled end cap 60 which is an integral part of an aspirator collar 61 illustrated in FIG. 5. 
     The aspirator collar 61 includes a cylindrical section 62 that contains the aspirator opening 57&#39;. The section 62 is inserted through a circular opening 63 in the end 17a&#39; of the regulator body 17&#39;. The collar 61 is retained in place by a snap ring 64 that fits within a groove 65 in the cylindrical section 62. An O-ring 66 prevents leakage past the interface between the cap 60 and the housing end 17a&#39;. 
     The cylindrical section 62 forms the outer wall of the space 56&#39; into which breathable gas is admitted when the flow control valve 19 opens. This breathable gas then passes through the aspirator opening 57&#39; to the outlet 21. A seal is achieved at the open end of the cylindrical section 62 by means of an O-ring 67 situated within a groove 68 formed in an outer section of the valve housing 20&#39;. 
     The diaphragm assembly used with the regulator 10&#39; is identical to that shown in the regulator 10 of FIGS. 2 and 3. By rotating the cap 60, the diver can change the location of the aspirator opening 57&#39; and accordingly change the amount of aspiration provided by the regulator 10&#39;. 
     Referring once again to FIG. 2, the regulator 10 is provided with a purge button 70 that is mounted on the diaphragm housing 17b. The purge button 70 includes a generally flat cap 70a formed integrally with a cylindrical section 70b which surrounds, but does not touch the diaphragm retainer 27. A peripheral flange 70c engages a shoulder 17c formed integrally with the housing 17b. A spring 71 situated between this shoulder 17c and the cap 70a biases the purge button 70 to the rest position shown in FIG. 2. 
     When the purge button 70 is manually depressed against the force of the spring 71, the interior surface 70d of the cap 70a pushes against the end 27a of the diaphragm retainer 27. This in turn displaces the shaft 28 in the direction of the arrow 40 so as to cause the valve 19 to open. The resultant flow of breathable gas through the valve 19 purges the regulator 10.