in an arrangement as shown in fig1 , an inhalation device consists of a main body 400 , which is generally cylindrical in cross section , with a mouthpiece section 405 at one end and an end cap 407 housing air inlets 420 at the other end . a known type of aerosol dispensing container 25 of generally cylindrical shape is housed within the main body of the device . the aerosol dispensing container has a stem 40 which contains an aerosol dispensing valve ( not shown ). the bore 15 is such that it forms an air tight seal on the stem 40 of the aerosol dispensing container 25 . a shoulder 45 limits and locates the position of the stem 40 , which in turn locates the aerosol dispensing container 25 in position in the main body 400 . a passage 50 extends from the bore 15 , continuing from the shoulder 45 to interconnect with a dispensing nozzle 55 . the opposite end of the dispensing container is contained within a sleeve 421 of similar cross section to the main body 400 . the longitudinal axis of both the sleeve 421 and main body 400 is generally coaxial . the sleeve is in loose sliding contact with the inner wall of the main body and may include several rebated grooves 430 in its walls to allow free passage of air in the main body past the sleeve . the sleeve 421 may be held in place by connection with a diaphragm 440 held in connection with the top of the main body 400 , as will now be described . thus , the sleeve 421 effectively hangs from the top of the main body . one end of an e . g ., molded flexible diaphragm 440 ( as shown alone in fig2 ) comprising a rigid disc - like section 441 , a flexible generally cylindrical wall section 445 and a diaphragm connection section 447 , is fitted around a inner sleeve groove 450 in the sleeve , e . g . by snap - fitting . a further molded lip 470 on the diaphragm 440 provides a snug fit for one end of a compression spring 460 . the compression spring is thus located and free to act on the sleeve . the other end of the compression spring is located by an annular shoulder 481 in a predominantly cylindrical flanged insert 480 housed in the top section of the main body 400 . this insert includes a groove 490 into which the disc - like section 441 of the flexible diaphragm 440 is snap - fitted . preferably , the multimaterial diaphragm is made using a multishot molding process wherein a first portion ( such as the disk ) is molded in a first step , and a second portion ( such as the flexure and ring ) is molded in a second step , and at the same time bonded to the first portion . with the improved diaphragm configuration of the invention , shown in fig2 , the relatively thick disk - portion “ a ” is molded from a rigid material ( relatively high stiffness ), which is particularly resistant to flexural deformation when the closed region 600 is at negative pressure , while the relatively thin flexure portion “ b ” is molded from an optimally flexible ( relatively low stiffness ) material , minimising the force required to move the inner sleeve and hence the forces required to be stored and released by the mechanism . the relatively thin flexure portion “ b ” is bonded to the disk - portion “ a ” along a continuous surface substantially parallel to the central axis of the diaphragm . the joint between the diaphragm connector section 447 and inner sleeve groove 450 is arranged to be air tight and the shape of the top surface of . the sleeve 422 to conform to the internal shape of the diaphragm such that in the rest position of the inhaler the two surfaces are in close proximity , and the enclosed space between them very small . the cylindrical flanged insert 480 is retained in place by the end cap 407 fitted into the main body of the device . this forms a chamber 590 between the air inlet slots 420 and the rigid part 441 of the diaphragm . the chamber is provided with one or more air pathways 580 such that air may pass from the air , inlet slots 420 to the mouthpiece 405 . the rigid disc - like section 441 of the diaphragm also includes a small valve port 495 which is normally covered by a valve seal ( flap ) 540 housed in a vane 550 pivotally connected to the cylindrical flanged insert 480 . the vane 550 in its rest position divides the chamber 590 between the air inlets 420 and the air pathways 580 that link to the mouthpiece such that it may move from its rest position by means of a pressure drop between the air inlets and the mouthpiece . on movement of the vane to the actuated position the valve seal ( flap ) 540 is sufficiently moved to open the valve port 495 . ( the vane 550 may be biased closed by a light spring flexure , a weight or a magnet not shown .) as shown in fig1 , the end of the main body having a pivot 500 has a recess adapted to receive a cam 520 integral with a dust cap 510 operating on the pivot . the recess further includes a passage communicating with a similar passage molded into the internal wall of the main body 400 . a camfollower 530 extending from the lower edge of the inner sleeve 421 acts on the cam such that when the dust cap is in the closed position the inner sleeve is forced by the camfollower to its uppermost position . when the dust cap is rotated to its open position the cam profile is such that the camfollower is free to move downwards by an amount sufficient to allow actuation of the device . in its rest position the dust cap 510 is closed , the camfollower 530 restrains the inner sleeve 421 in its uppermost position such that the enclosed space trapped between the diaphragm 440 and the top surface 422 of the inner sleeve is at a minimum and the spring 460 is compressed . the valve port 495 is closed by the valve seal ( flap ) 540 and the sleeve 421 is clear of the top of the aerosol can 25 which is thus unloaded . the dust cap is opened rotating the integral cam 520 allowing the camfollower 530 to drop by amount aa . the inner sleeve is forced downwards under the action of the spring 460 . as the inner sleeve moves downwards the enclosed volume between the diaphragm 440 and inner sleeve is increased by a linear equivalent amount a ′ a ′, less than or equal to aa . since the valve port 495 is closed this creates a low pressure volume or near vacuum in the closed region 600 [ fig3 ]. the effect of the pressure differential between the closed region 600 and atmospheric pressure is such that the inner sleeve tends to resist the action of the spring . as the inner sleeve moves downwards it contacts the aerosol can 25 and begins compression of the aerosol valve ( not shown ). downward movement of the inner sleeve will continue until there is a balance of forces between the compressive force in the spring 460 and resisting forces created by the pressure differential and compression of the aerosol valve . the geometry of the device is arranged such that this balance occurs before the aerosol valve has been sufficiently compressed to actuate it . a typical chlorofluorocarbon ( cfc ) aerosol medicament container requires about 20n force to actuate , while a typical hydrofluoroalkane ( hfa ) aerosol medicament container requires about 40n force to actuate . thus , depending upon the application , the spring 460 should provide a force 10 % to 50 % greater than the required actuation force of the medicament container . as is known , cfc containing propellants have been shown to liberate chlorine in the stratosphere and cause ozone depletion . because of this danger , the montreal protocol was signed that bans the use of cfcs . metered - dose inhalers ( mdis ) for treating asthma and other respiratory diseases were exempted from this general ban , although this exemption is temporary and will be lifted as substitute products become available . the first such substitute , hfa propellant , has been on the market for about a year . it may also be possible to arrange for the balance of forces to take place before the inner sleeve has contacted the aerosol can , such that the spring force is balanced by the resisting force produced on the inner sleeve by virtue of the pressure differential . on inhalation by the patient through the mouthpiece 405 , a small pressure differential is created across the vane 550 which is pivoted towards one end . the pressure differential causes the vane to move from the rest position to the actuated position . the vane 550 and design of the air passageway 580 in the chamber 590 are such that in the actuated position air can flow freely from the air inlets 420 to the patient . the movement of the vane 550 causes the valve seal ( flap ) 540 to be moved out of a sealing position with the valve port 495 . opening the valve port allows air into the closed region 600 between the diaphragm and inner sleeve such that the enclosed space reaches atmospheric pressure . this causes an imbalance of forces acting on the sleeve 421 and container 25 . the sleeve and container are thus forced downwards by the spring 460 resulting in the release of a measured dose of medicament through the dispensing nozzle 55 and into the mouthpiece at the same time as the patient breathes in . thus , the patient inhales air with a metered dose of medicament . after the inhalation of the dose by the patient , the dust cap 510 is returned to its closed position . this rotates the cam 520 and causes the camfollower 530 to be forced upwards . this in turn acts on the inner sleeve 421 moving it upwards to compress the spring 460 and close the closed region 600 between the diaphragm and inner sleeve top surface 422 . this forces air out of the closed region 600 which escapes through the valve port 495 lifting the valve seal ( flap ) 540 . since the valve seal ( flap ) is only lightly biased to its closed position it presents little resistance to air flow out of the enclosed space . the aerosol can is free to return to the rest position under the action of its own aerosol valve spring . in use the patient loads the aerosol dispensing container into the main body . the aerosol container may be loaded by providing a coarse threaded screw in the main body 400 , for example about the line i - i . when part of the main body 400 has been unscrewed , the aerosol can be inserted . the main body 400 can then be replaced locating the inner sleeve over the top end of the can , and the device is ready for use . as described previously , the device could be manufactured as a sealed unit . the device may be provided with means to provide a regulated air flow to the user or inhaler . thus a sonic device , e . g ., a reed , may be provided which sounds when the inspired air flow is greater than a pre - set level , e . g ., above 30 to 50 litres per minute . the sonic device may be located in the mouthpiece 95 or below the air inlet 421 . the sound produced warns the patient to breathe at a lower rate . the device may also be provided with a means such that it will not operate below a certain pre - determined air flow rate , e . g . 10 to 30 litres per minute . in one embodiment the vane 550 will be biased by a spring such that the predetermined minimum air flow is necessary for it to move to its actuated position and enable the valve seal to open . the main body of a dispensing device , as described in the above embodiment of this invention is preferably manufactured from a plastic such as polypropylene , acetal or moulded polystyrene . it may however be manufactured from metal or another suitable material . referring to fig4 - 8 another diaphragm assembly 640 and actuator assembly according to the present invention for use with the medicament dispenser of fig1 are shown . the diaphragm assembly 640 and the actuator assembly of fig4 - 8 are similar to the diaphragm assembly 440 and the actuator assembly of fig2 and 3 , such that similar elements are provided with the same reference numerals . the molded flexible diaphragm 640 includes a rigid disc - like section 641 , a flexible generally cylindrical wall section , or annular flexure 645 , and a thicker connector section , or peripheral attachment ring 647 . a central portion 700 is unitarily formed with and extends radially inwardly from the annular flexure 645 . the central portion preferably is provided in the form of a central portion 700 bonded along a top surface to a bottom surface of the rigid disc - like section 641 , i . e ., surfaces substantially traverse to the central axis of the diaphragm 640 . referring to fig6 and 7 , the relatively thick disk - portion “ a ” which includes the disc - like section 641 of the diaphragm 640 , is molded from a rigid material ( relatively high stiffness ) such as acrylonitrile butadiene styrene ( abs ), which is particularly resistant to flexural deformation when the closed region 600 is at negative pressure . the relatively thin flexure portion “ b ” which includes the central portion 700 , the annular flexure 645 and the peripheral attachment ring 647 , is molded from an optimally flexible material ( relatively low stiffness ) such as a thermoplastic elastomer ( tpe ), permitting high performance . preferably , the multimaterial diaphragm 640 is made using a multishot molding process wherein the first portion “ a ” is molded in a first step , and the second portion “ b ” is molded in a second step , and at the same time bonded to the first portion . as shown in fig4 through 7 , the central portion 700 and the rigid disc - like section 641 both define a central upwardly extending boss 702 for additional strength . in addition , the rigid disc - like section 641 includes an outer axial wall 704 which provides further strength to the diaphragm 640 . the central portion 700 includes axial walls 706 which are received within and bonded to axial grooves 708 of the rigid disc - like section 641 , thereby providing bonding surfaces substantially parallel with the central axis of the diaphragm 640 and increasing the total bonding surface area between the central portion 700 and the rigid disc - like section 641 . referring also to fig8 , the peripheral attachment ring 647 of the diaphragm 640 is fitted around an annular wall 451 of the sleeve 421 and is secured in an air - tight manner thereon with a retainer ring 800 , which is secured to the sleeve 421 , e . g ., by snap - fitting into an annular groove 452 of the sleeve . the retainer ring 800 also provides a snug fit for one end of the compression spring 460 , such that the compression spring is thus located and free to act on the sleeve 421 . the cylindrical flanged insert 480 housed in the top section of the main body 400 of the inhaler includes a protrusion 491 which is snap fit into a radially outwardly facing circumferential groove 710 of the relatively rigid disc - like section 641 of the flexible diaphragm 640 . the valve port 690 of the diaphragm 640 passes through the rigid disc - like section 641 and the central portion 700 of the diaphragm . the valve port 690 is closed by the valve seal ( flap ) 540 , which is biased closed by a fiat spring 802 , as shown in fig8 . the rigid disc - like section 641 of the diaphragm includes protrusions 712 extending upwardly therefrom that receive and correctly position the flat spring 802 . the rigid disc - like section 641 of the diaphragm 640 also includes a baffle 714 on a top surface thereof for substantially preventing air flow between the valve seal ( flap ) 540 and the diaphragm . the baffle 714 closely follows the profile of the underside of the flap 540 , yet provides sufficient clearance for the flap to open upon breath - actuation . the rigid disc - like section 641 of the diaphragm 640 additionally includes an assembly location key 716 for use in correctly assembling the diaphragm 640 within the actuator assembly of fig8 . the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the present embodiments are therefore to be considered in all respects illustrative and not restrictive , the scope of the invention being indicated by the appended claims rather than by the foregoing description , and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein . although the invention herein has been described with reference to particular embodiments , it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention . it is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims .
a metered dose inhaler for use with a pressurized aerosol container which is preferably breath - actuated . a preload is applied to the internal aerosol valve by an amount sufficient to result in a dose release , but this is prevented by the application of a pneumatic resisting force . the inhaler comprises a release device which , upon actuation , releases the resisting force and allows the preload to actuate the aerosol valve . a metered dose of medicament is then released for inhalation by the patient . the pneumatic resisting force is established by a negative pressure region defined in part by a diaphragm . the diaphragm includes a central disk of a first , relatively high stiffness material and a peripheral ring , coupled by a flexure of a second , relatively low stiffness material .