GB2547944A

GB2547944A - Diaphragm pump

Info

Publication number: GB2547944A
Application number: GB1603768.1A
Authority: GB
Inventors: Louis Tyers Gary
Original assignee: Intelligent Energy Ltd
Current assignee: Intelligent Energy Ltd
Priority date: 2016-03-04
Filing date: 2016-03-04
Publication date: 2017-09-06
Also published as: GB201603768D0

Abstract

Pump 1 comprising an elastic membrane 2 compressed between two plates 3, 4, the plates collectively defining an inlet port 5 and valve chamber 6, outlet port 7 and valve chamber 8, pump port 9 and chamber 10, and communication channels 11, 12, 13. The membrane comprises a non-return inlet flap valve 14 adjacent the inlet port, an outlet flap valve 15 adjacent the outlet valve chamber, and a diaphragm portion 16 between the pump port and pump chamber. The flaps may be smaller in area than their adjacent valve chambers into which they may be resiliently displaced, and greater than the diameter of a port or plate opening against which they are seated. An outlet communication channel may link the pump chamber and outlet valve chamber. Channels between chambers may be located in the plate face adjacent the membrane. The inlet port may be open 20 on the membrane-facing face 18 of one plate, and also the opposite side 19 of that plate. An outlet port may open on the same external face as the inlet port, and connect to the outlet valve chamber. A dome-shaped control valve 22 with at least two slits 25 in cross-shape orientation defining displaceable leafs may be provided between the pump chamber and outlet valve chamber, and may open only when pressure exceeds a predetermined differential.

Description

DIAPHRAGM PUMP

The present invention relates to diaphragm pumps for pumping fluids. A conventional diaphragm pump generally comprises a flexible diaphragm which is displaceable to pressurise fluid in a chamber having an inlet and an outlet each with a respective non-return valve. The non-return valves ensure that pressurization and depressurization in the chamber caused by diaphragm displacement enable flow in a single direction through the pump. A number of technological applications require the use of miniature pumps and there is a continuing need to reduce the size, complexity and cost of manufacture of such diaphragm pumps.

It is an object of the invention to provide a compact and easily manufactured diaphragm pump.

According to one aspect, the present invention provides a pump comprising: an elastic membrane held in compression between two plates, the two plates together defining an inlet port, an inlet valve chamber, an outlet port, an outlet valve chamber, a pump port and a pump chamber, and communication channels; the elastic membrane having: an inlet flap portion defining an inlet non-return valve component adjacent the inlet port; an outlet flap portion defining an outlet valve component adjacent the outlet valve chamber; a diaphragm portion disposed between the pump port and the pump chamber. A first one of the plates may define the inlet port having a first cross-sectional area smaller than the area of the inlet flap portion against which the inlet flap portion seats. A second one of the plates may define the inlet valve chamber having a cross sectional area larger than the inlet flap portion into which the inlet flap portion may be displaced. The first one of the plates may define an outlet valve chamber having a first cross-sectional area larger than the area of the outlet flap portion into which the outlet flap portion may be displaced. The second one of the plates may define an outlet communication channel having an opening with a cross sectional area smaller than the area of the outlet flap portion against which the outlet flap portion seats. The outlet communication channel may extend between the pump chamber and the outlet communication channel opening.

The first one of the plates may have a first face in contact with the elastic membrane and a second face opposite the first face, and the inlet port may include an opening in the second face of the first plate. The first one of the plates may have a first face in contact with the elastic membrane and a second face opposite the first face, and the outlet valve chamber may extend from the first face to the outlet port which extends from the second face.

The pump may include a control valve. The elastic membrane may further define a control valve flap portion defining an asymmetric valve component adjacent the outlet port. The first one of the plates may define a control valve upstream chamber in communication with the outlet valve chamber and into which the control valve flap portion extends. The second one of the plates may define a control valve downstream chamber in communication with the outlet port. The control valve flap portion may comprise a moulded shape having at least one slit configured to allow forward passage of fluid therethrough from the control valve upstream chamber to the control valve downstream chamber only when the pressure differential across the control valve exceeds a first predetermined threshold.

The control valve flap portion may comprise a dome shape extending into the control valve upstream chamber which may have at least two slits in cross-wise configuration defining leafs resiliently biased to normally-closed positions but displaceable to open positions under the first predetermined pressure differential.

The control valve flap portion may be configured to return to a closed configuration when the pressure differential falls to a second predetermined pressure differential less than the first pressure differential. The control valve flap portion may be configured to return to its dome-shaped closed configuration with a snap action which provides a back pressure to the outlet valve flap portion. A first one of the communication channels may extend between the inlet valve chamber and the pump chamber in a first face of a second one of the plates, the first face being in contact with the elastic membrane. A second one of the communication channels may extend between the pump chamber and the outlet valve in the first face of the second plate. A third one of the communication channels may extend from the outlet valve chamber to the control valve upstream chamber in a first face of the first one of the plates, the first face being in contact with the elastic membrane.

The inlet flap portion and/or the outlet flap portion may each comprise a displaceable portion of the elastic membrane incompletely surrounded by a cut in the membrane such that the displaceable portion can be flexed out of the plane of the membrane about a hinge portion of the membrane. The displaceable portion incompletely surrounded by the cut may have a diameter greater than the diameter of a port or opening in the plate against which the displaceable portion seats and smaller than the diameter of a chamber in the plate into which it can be resiliently displaced.

The two plates of the pump may include a snap fit or friction fit connection mechanism for quick assembly of the pump with the elastic membrane held between the plates. The elastic membrane may comprise an injection moulded membrane. The pressure differential required to open the control valve may exceed a pressure differential required to open the outlet valve. The outlet flap portion may define a component of an outlet valve comprising a control valve, the flap portion defining an asymmetric valve component adjacent the outlet port.

The pump as defined above may be incorporated into a fuel cartridge having a first reactant in a first chamber, the fuel cartridge being configured to pump first reactant fluid from the first chamber to a second reactant to thereby generate fuel.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of the main components, in exploded form, of a diaphragm pump, viewed from the side and below;

Figure 2 shows a perspective view of the same components of the diaphragm pump of figure 1, viewed from the side and above;

Figure 3 shows a perspective cross-sectional view of part of the same components of the pump of figures 1 and 2, from the side and above;

Figure 4 is a top plan view of an elastic membrane component of the diaphragm pump of figures 1 to 3;

Figure 5 is a side view of the elastic membrane component of figure 4 and the diaphragm pump of figures 1 to 3;

Figure 6 is a schematic cross-sectional view of the functional component parts of the diaphragm pump of figures 1 to 3 shown in linear relationship:

Figure 7 is a schematic cross-sectional view of an alternative and simplified version of a diaphragm pump similar to that shown in figure 6, without anti-siphon functionality;

Figure 8 is a schematic cross-sectional view of an alternative and simplified version of a diaphragm pump similar to that shown in figure 6, with a combined non-return and anti-siphon valve component.

Throughout the present specification, any descriptors relating to relative orientation and position, such as "top", "bottom", "horizontal”, "vertical", "left", "right", "up", "down", "front", "back", as well as any adjective and adverb derivatives thereof, are used in the sense of the orientation of the diaphragm pump and its components as presented in the drawings. However, such descriptors are not intended to be in any way limiting to an intended use of the described or claimed invention.

With reference to figures 1 and 2, there is shown a diaphragm pump 1 which can be fabricated from as few as three components, plus any external connector fittings required. The pump 1 comprises a first plate 3 (which can conveniently be labelled as a top plate) and a second plate 4 (which can conveniently be labelled as a bottom plate), and an elastic membrane 2 disposed between the two plates 3, 4. The elastic membrane is constrained between the top and bottom plates, e.g. held in compression and firmly in place between the two plates by pressure applied by the plates, although the drawings show the components separated for clarity of explanation.

The top plate 3 defines an inlet port 5 extending through the plate 3 suitable for receiving or being otherwise engaged with or coupled to an inlet connector 55 (visible in figure 2) which could be in threaded engagement with the top plate 3. The inlet connector 55 may comprise a push-fit connector for example, which could be in threaded engagement with the top plate 3. The top plate 3 also defines a pump port 9, an outlet valve chamber 8, a control valve upstream chamber 23 and a communication channel 13 extending between the outlet valve chamber 8 and the control valve upstream chamber 23. The communication channel 13 will, for convenience, be referred to herein as the third communication channel.

The bottom plate 4 (best seen in figure 2) defines an inlet valve chamber 6, a pump chamber 10 and a communication channel 11 (referred to as the first communication channel) extending between the inlet valve chamber 6 and the pump chamber 10. The bottom plate 4 also defines a communication channel 12 (referred to as the second communication channel) extending from the pump chamber 10 to an opening or recess 17. The bottom plate 4 also defines a control valve downstream chamber 24, and an outlet port 7 extending through the thickness of the plate. The outlet port 7 may be suitable for receiving or being otherwise engaged with or coupled to an outlet connector 56 (visible in figure 1). The outlet connector 56 may comprise a push-fit connector 56 for example, which could be in threaded engagement with the bottom plate 4.

The elastic membrane 2 comprises a sheet of elastic material such as an elastomeric compound which defines an inlet flap portion 14, an outlet flap portion 15, a diaphragm portion 16, and a control valve flap portion 22. The inlet flap portion 14 may be formed as a generally circular cut-out portion remaining connected to the rest of the membrane 2 by a hinge portion 30. Similarly, the outlet flap portion 15 may be formed as a generally circular cut-out portion remaining connected to the rest of the membrane 2 by a hinge portion 31. The diaphragm portion 16 may comprise a suitable area of the membrane 2 without modification, although a specially modified area of the membrane 2 could be provided such as a thickened portion as shown in figures 2, 3 and 5, e.g. if required to alter the resilient properties of the membrane specifically at the pump chamber 10. The control valve flap portion 22 comprises a dome-shaped portion of the membrane having at least one slit 25 cut through the membrane in the dome. In the preferred arrangement shown, the dome-shaped portion has two slits 25 cut in a crosswise configuration. The cross-slits effectively define leafs in the membrane which are biased to normally closed positions, but are displaceable to open positions under a requisite pressure differential as will be described below. A single slit 25 may function satisfactorily, for example where the action of inversion of the dome by a requisite pressure differential forces apart the edges of a slit across the dome apex.

The top plate 3, the bottom plate 4 and the elastic membrane 2 have, respectively, a set of holes 50, 51, 52 extending therethrough in mutual alignment for the purposes of clamping the plates together with the membrane in compression therebetween, using a set of bolts or screws for example. In the example shown, six holes in each component are shown for clamping the assembly together. However, a different number of fixing points may be used according to the size and nature of the materials of the components, to ensure that a fluid tight set of enclosures can be maintained, as will be explained later. Other ways of clamping the assembly together may be considered, such as one or more external clamps or glue or other bonding agent, or by providing snap-fit or friction fit features to the plates 3,4 so that they can snap-fit or friction fit together for quick-assembly.

Figure 3 shows parts of the components and features described in connection with figures 1 and 2 in a cross-sectional form showing particularly the profile of the pump port 9, the control valve upstream chamber 23, the dome-shaped control valve flap portion 22, the pump chamber 10 and the control valve downstream chamber 24.

Figures 4 and 5 show the features of the elastic membrane 2 in greater detail, in particular the inlet flap portion 14 and the outlet flap portion 15, the diaphragm portion 16, and the dome-shaped portion of the membrane with cross slits 25 providing the control valve flap portion 22. Figure 4 also shows the hinge portion 30 which provides a flexing function to the inlet flap portion 14 so that the inlet flap 14 can, under pressure, resiliently flex out of the plane of the rest of the membrane by virtue of the semi-circular cut-out 32 (or semicircular cut line) which incompletely / partially surrounds the displaceable inlet flap portion 14. Similarly, the hinge portion 31 provides a flexing function to the outlet flap portion 15 so that the outlet flap 15 can, under pressure, resiliently flex out of the plane of the rest of the membrane by virtue of the semi-circular cut-out 33 (or semi-circular cut line) which incompletely / partially surrounds the displaceable outlet flap portion 15.

Operation of the diaphragm pump will now be described in detail with reference to the schematic cross-sectional view of figure 6. The schematic view of figure 6 is represented in slightly different form than the arrangements of figures 1 to 5 such that all four main components of the diaphragm pump 1 are sectioned in one cross-section. The diaphragm pump 1, in this embodiment, comprises: (i) an inlet non-return valve comprising inlet port 5, inlet flap portion 14, and inlet valve chamber 6; (ii) a pump comprising pump port 9, diaphragm 16, and pump chamber 10; (iii) an outlet non-return valve comprising opening 17, outlet flap portion 15, and outlet valve chamber 8; (iv) an anti-siphon control valve comprising control valve upstream chamber 23, control valve flap portion 22, control valve downstream chamber 24 and outlet port 7.

The inlet valve is fluidly coupled to the pump by way of the first communication channel 11; the pump is fluidly coupled to the outlet valve by way of the second communication channel 12; and the outlet valve is fluidly coupled to the control valve by way of the third communication channel 13.

It will be recognised that these components can be disposed in any suitable two dimensional layout within the planes of the plates 3, 4 such as shown in figures 1 to 3, or can be disposed in a linear layout within the planes of the plates 3, 4, as illustrated in figure 6.

Inlet fluid is provided at inlet opening 20 in the top plate 3 via a suitable connector and fluid conduit (not shown in figure 6). Inlet port 5 extends through the top plate 3 from a first (e.g. inside) face 18 to the opening 20 at a second (e.g. outside) face 19 of the plate. Inlet flap portion 14 defines an inlet non-return valve component which is adjacent to the inlet port 5 and seats against the first (inside) face 18 of the top plate 3, because the flap portion 14 is larger in diameter than the inlet port 5. However, the inlet flap portion 14 is displaceable, under a pressure differential, into the inlet valve chamber 6 which is larger in diameter than the inlet flap portion 4. When there is a forward pressure differential (i.e. the pressure in chamber 6 is lower than the inlet pressure at inlet port 5), the inlet flap portion 14 displaces into the chamber 6 (as shown in dashed outline in figure 6) against a natural bias provided by the resilience of the elastic membrane. When there is no pressure differential across the inlet valve, the flap portion 14 returns under the natural resilience of the elastic material to the in-plane position indicated by the unbroken lines in figure 6. Under reverse pressure differential (i.e. the pressure in chamber 6 is higher than the inlet pressure at inlet port 5), the inlet flap portion 14 is pressed firmly against the first face 18 of the top plate 3, thereby sealing the inlet valve shut.

The pump is actuated by a suitable plunger or other actuator extending through the pump port 9 in the top plate 3, as indicated schematically with the actuator arrow in figure 6. The actuator displaces the diaphragm portion 16 of the membrane 2 to a displacement position within the pump chamber 10 in the bottom plate 4, as indicated by the dashed lines in figure 6. Fluid displaced within the pump chamber 10 by the displacement of the diaphragm portion 16 of the membrane 2 cannot flow backwards through the first communication channel 11 and through the inlet valve because it is blocked by the nonreturn action of the flap portion 14 when the pressure in inlet valve chamber 6 rises above the pressure at the inlet port 5. Instead, fluid that is displaced from the pump chamber 10 by the diaphragm portion 16 as it moves to the displacement position (dashed lines) is directed along the second communication channel 12 to the opening 17 of the outlet valve.

Outlet flap portion 15 of the membrane 2 defines an outlet non-return valve component which is adjacent to the opening 17 of the outlet valve and seats against the first (inside) face 28 of the bottom plate 4, because the flap portion 15 is larger in diameter than the opening 17. However, the outlet flap portion 15 is displaceable, under a forward pressure differential, into the outlet valve chamber 8 which is larger in diameter than the outlet flap portion 15. When there is a forward pressure differential (i.e. the pressure in the outlet valve chamber 8 is lower than the pressure at opening 17), the outlet flap portion 15 displaces into the chamber 8 (as shown in dashed outline in figure 6) against a natural bias provided by the resilience of the elastic membrane. When there is no pressure differential across the outlet valve, the flap portion 15 returns under the natural resilience of the elastic material to the in-plane position indicated by the unbroken lines in figure 6. Under reverse pressure differential (i.e. the pressure in chamber 8 is higher than the pressure at the outlet valve opening 17), the outlet flap portion 15 is pressed firmly against the first face 28 of the bottom plate 4, thereby sealing the outlet valve shut.

When the diaphragm portion 16 of the pump returns to its rest position in the plane of the membrane (as shown in solid lines in figure 6), the pressure in pump chamber 10 will drop causing a corresponding pressure drop in inlet valve chamber 6, thereby opening the inlet valve flap portion 14 to admit more fluid from the inlet port 5. Fluid is prevented from refilling the pump chamber 10 from the outlet because the reverse pressure differential applied across the outlet valve flap portion 15 closes and seals against the first (inside) face 28 of bottom plate 4 at the opening 17.

The inlet non-return valve 5, 14, 6; the pump 9, 16, 10; and the outlet non-return valve 17, 15, 8 thereby together act in concert as a diaphragm displacement pump. A further feature of the diaphragm pump 1 of figure 6 is an anti-siphon or control valve. The control valve receives fluid from the outlet non-return valve via the third communication channel 13 which communicates with the control valve upstream chamber 23. The dome-shaped control valve flap portion 22 requires a larger forward pressure differential for it to be displaced to an open condition as indicated by the dashed lines in figure 6, e.g. the pressure in the control valve upstream chamber 23 must be greater than that in the control valve downstream chamber 24 by more than a nominal amount, and generally by more than the forward pressure differential required to open the outlet valve flap portion 15 in the outlet valve. Once the forward pressure differential across the control valve flap portion 22 reaches a predetermined amount, the dome may invert and the flaps or leafs defined by the slits 25 may open to allow forward fluid flow through the control valve to the outlet port 7.

Preferably, the control valve flap portion 22 provides asymmetric opening and closing pressures to the control valve. The control valve flap portion 22 may provide an opening pressure threshold PI which can be provided and exceeded by the impulse of the pump when pump diaphragm portion 16 is actuated, and a closing pressure threshold P2, less than PI, such that the pump will be sure to close positively and fully when the pressure falls from PI to P2. The return of dome-shaped flap portion 22 to its rest position (unbroken lines) may be by a snap displacement back to its dome-shaped rest position. This may provide a small return pressure impulse which forces firm closure of the outlet valve flap portion 15. The required pressure PI on the dome to open the control valve may also provide an anti-siphoning action. Moderate pressure differentials across the diaphragm pump 1 where the pressure at the outlet 7 falls below that at the inlet 20 such as may be caused by a siphoning action can be prevented from causing flow through the pump by profiling the control valve flap portion 22 to have its opening pressure PI sufficiently high to resist opening by siphoning action, but sufficiently low to enable opening by the pump diaphragm 16 displacement action.

In a general aspect, the elastic membrane 2 may be engineered to provide the control valve flap portion 22 with an asymmetric opening and closing action where the pressure required to open the valve is greater than the pressure allowing closing of the valve. The elastic membrane 2 may be engineered to provide the control valve flap portion with a closing force or impulse which back-pressurises the inlet and outlet valves of the diaphragm pumps to ensure correct operation thereof. The elastic membrane 2 may be engineered to provide the control valve flap portion 22 with an opening force / pressure requirement that is greater than the opening force / pressure required by the outlet valve flap portion 15, thereby resisting any hydrostatic head of a fluid reservoir feeding the inlet port 5 and preventing forward fluid flow leakage past the pump. The control valve may provide a stabilizing and/or metering effect to the diaphragm pump 1. The control valve may generally be tuned to match or exceed a likely hydrostatic head of fluid at the inlet and/or resist any siphoning pressure at the outlet.

The characteristics required of the control valve, and of the inlet valve, outlet valve and the diaphragm can all be established by engineering the respective regions of the elastic membrane 2 accordingly. Injection moulding may be a suitable manufacturing technique to provide a suitably engineered membrane 2 with appropriate resilient and other characteristics at the required positions for the inlet valve, the pump, the outlet valve and the control valve. The elastic membrane may have uniform thickness across a major part of its surface or may be locally varied for the flap portions or diaphragm portions, for example. Shapes, other than the dome-shape of the control valve flap portion, may be suitable to provide a suitable moving part for the control valve to have asymmetric opening and closing action, e.g. exhibiting hysteresis in the opening and closing action. Other convex / concave shapes may be appropriate. By appropriate sizing of the various chambers and ports, it may be possible to realise a design of pump 1 which uses a uniform elastic material across its whole, or a major part of its whole, surface area.

Figure 9 illustrates a number of possible variations of the engineered membrane 2. Figure 9a illustrates a membrane 2a of uniform thickness such that each of the flap portions 14, 15, the diaphragm portion 16 and the dome-shaped control valve flap portion 22 have the same thickness (the dome-portion 22 having an excursion of the uniform thickness membrane out-of-plane). Figure 9b illustrates a membrane 2b of uniform thickness except for a thickened portion for the diaphragm portion 16, resulting in an increased relative thickness of the diaphragm portion only. This increases the effort required to depress the diaphragm part of the membrane and thereby to actuate the pump, and also increases the force that the diaphragm exerts on the return stroke. Figure 9c illustrates a thicker membrane 2c than shown in figures 9a and 9b. In figure 9c, the membrane is of uniform thickness except for a thinner portion for the diaphragm portion 16, such that each of the flap portions 14, 15 and the dome-shaped control valve flap portion 22 have a greater resistance to displacement than the diaphragm portion. This decreases the effort required to actuate the pump but raises the effort required to open the valves. Figure 9d shows a variant membrane 2d in which the diaphragm portion 16 and the control valve flap portion 22 have relatively thin membrane while the inlet valve and outlet valve flap portions 14,15 are relatively thick, to increase the effort required to open the inlet and outlet valves relative to the effort required to actuate the pump diaphragm and control valve. Figure 9e illustrates a membrane 2e of uniform thickness except for a thickened portion at the domeshaped control valve flap portion 22 such that each of the flap portions 14, 15 and the diaphragm portion 16 have the same thickness but the dome-portion 22 requires more effort for actuation. Other variations can be implemented according to the specific requirements of any particular diaphragm pump application.

Although the inlet valve flap portion 14 is described in the arrangement of figure 6 as having a larger diameter than the inlet port 5, it will be recognised that for non-circular arrangements of flap portion 14 and/or port 5, a more general condition would be that the inlet flap portion 14 has a surface area which is greater than the cross-sectional area of the inlet port 5, such that it is able to completely occlude the port 5. Although the inlet flap portion 4 is described as having a smaller diameter than the inlet valve chamber 6, it will be recognised that for non-circular arrangements of the flap portion 14 and/or valve chamber 6, a more general condition would be that the inlet flap portion has a smaller area than the cross-sectional area of the valve chamber 6 such that the flap portion 14 can be displaced into the valve chamber 6.

Similarly, although the outlet valve flap portion 15 is described in the arrangement of figure 6 as having a larger diameter than the opening 17, it will be recognised that for non-circular arrangements of flap portion 15 and/or opening 17, a more general condition would be that the outlet flap portion 15 has a surface area which is greater than the cross-sectional area of the opening 17, such that it is able to completely occlude the opening 17. Although the outlet flap portion 15 is described as having a smaller diameter than the outlet valve chamber 8, it will be recognised that for non-circular arrangements of the flap portion 15 and/or valve chamber 8, a more general condition would be that the outlet flap portion has a smaller area than the cross-sectional area of the valve chamber 8 such that the flap portion 15 can be displaced into the valve chamber 8.

Figure 7 shows a somewhat simplified version of a diaphragm pump, where the special functionality of the control valve is not required. In this arrangement, the control valve elements of the upstream chamber 23, the downstream chamber 24, and the domeshaped flap portions 22 are omitted. The outlet port 7 can thus be provided directly from the outlet valve chamber 8, to the second surface 19 of the top plate 3. Alternatively, the outlet port could be provided to a lateral edge of the top plate 3 by way of a communication channel such as that shown as item 13 in figure 6.

Figure 8 shows another simplified version of a diaphragm pump, where the special functionality of the control valve is combined with the outlet valve functionality. In this arrangement, the outlet non-return valve functionality and the control valve functionality are combined in a single control valve. In this arrangement, the slits 25 of the control valve are engineered so that the dome-shape can be inverted and the slits opened by the pressure of the pump diaphragm, when actuated, but the slits are strong enough to remain closed when the reverse pressure caused by the return of the diaphragm to its rest position is applied so that the control valve is an effective non-return valve over the expected reduced pressure ranges caused by the diaphragm return action. In accordance with the arrangement of figure 6, the dome-shaped flap portion 22 may be engineered to have a closing pressure lower than the opening pressure in the forward direction such that the control valve will have already closed or started closing as the diaphragm portion 16 returns to its rest position.

The first, second and third communication channels 11, 12, 13 have been exemplified in figures 1 to 8 as channels in the first surfaces 18, 28 of their respective top and bottom plates 3, 4 but it will be recognised that these communication channels could be provided within the body of the respective plate. However, for manufacturing simplicity, it may be preferred to form the channels in the first surfaces as shown where they will be conveniently covered and closed by the elastic membrane 2 along the appropriate parts of their lengths. The inlet port 5 and outlet port 7 have been exemplified in figures 1 to 8 as ports passing through the respective plates 3, 4 from first surface 18 or 28 to second surface 19 or 29. However, it will be understood that edge opening ports could be provided by channels running along the respective first surfaces 18 or 28 of the plate from the position of the inlet valve or outlet valve to a peripheral edge of the plates 3, 4 where a suitable connection could be made.

The diaphragm pumps 1 as described herein may have particular use and application in fuel cartridges where a small and accurately controlled intermittent flow of fluid is required, for example to deliver small quantities of reactant fluid such as water to fuel pellets in a reaction chamber, to result in the generation of hydrogen in the reaction chamber. Thus, in a general aspect, a fuel cartridge may have a first reactant (such as water) in a first chamber (such as a fluid reservoir) and a diaphragm pump as described above may be coupled between the first chamber and a reaction chamber comprising a second reactant. When hydrogen generation is required, a small and/or metered volume of first reactant can be pumped to the reaction chamber.

Other applications for such diaphragm pumps are readily envisaged.

Other embodiments are intentionally within the scope of the accompanying claims.

Claims

1. A pump comprising: an elastic membrane held in compression between two plates, the two plates together defining an inlet port, an inlet valve chamber, an outlet port, an outlet valve chamber, a pump port and a pump chamber, and communication channels; the elastic membrane having: an inlet flap portion defining an inlet non-return valve component adjacent the inlet port; an outlet flap portion defining an outlet valve component adjacent the outlet valve chamber; a diaphragm portion disposed between the pump port and the pump chamber.

2. The pump of claim 1 in which a first one of the plates defines the inlet port having a first cross-sectional area smaller than the area of the inlet flap portion against which the inlet flap portion seats, and a second one of the plates defines the inlet valve chamber having a cross sectional area larger than the inlet flap portion into which the inlet flap portion may be displaced.

3. The pump of claim 2 in which the first one of the plates defines an outlet valve chamber having a first cross-sectional area larger than the area of the outlet flap portion into which the outlet flap portion may be displaced, and the second one of the plates defines an outlet communication channel having an opening with a cross sectional area smaller than the area of the outlet flap portion against which the outlet flap portion seats, the outlet communication channel extending between the pump chamber and the outlet communication channel opening .

4. The pump of claim 2 in which the first one of the plates has a first face in contact with the elastic membrane and a second face opposite the first face, and the inlet port includes an opening in the second face of the first plate.

5. The pump of claim 3 in which the first one of the plates has a first face in contact with the elastic membrane and a second face opposite the first face, and the outlet valve chamber extends from the first face to the outlet port which extends from the second face.

6. The pump of claim 3 further including a control valve, and wherein: the elastic membrane further defines a control valve flap portion defining an asymmetric valve component adjacent the outlet port; the first one of the plates defines a control valve upstream chamber in communication with the outlet valve chamber and into which the control valve flap portion extends; and the second one of the plates defines a control valve downstream chamber in communication with the outlet port.

7. The pump of claim 6 in which the control valve flap portion comprises a moulded shape having at least one slit configured to allow forward passage of fluid therethrough from the control valve upstream chamber to the control valve downstream chamber only when the pressure differential across the control valve exceeds a first predetermined threshold.

8. The pump of claim 7 in which the control valve flap portion comprises a dome shape extending into the control valve upstream chamber and having at least two slits in cross-wise configuration defining leafs resiliently biased to normally-closed positions but displaceable to open positions under the first predetermined pressure differential.

9. The pump of claim 8 in which the control valve flap portion is configured to return to a closed configuration when the pressure differential falls to a second predetermined pressure differential less than the first pressure differential.

10. The pump of claim 8 in which the control valve flap portion is configured to return to its dome-shaped closed configuration with a snap action which provides a back pressure to the outlet valve flap portion.

11. The pump of any preceding claim in which: a first one of the communication channels extends between the inlet valve chamber and the pump chamber in a first face of a second one of the plates, the first face being in contact with the elastic membrane, and a second one of the communication channels extends between the pump chamber and the outlet valve in the first face of the second plate.

12. The pump of claim 11 when dependent from claim 6 in which: a third one of the communication channels extends from the outlet valve chamber to the control valve upstream chamber in a first face of the first one of the plates, the first face being in contact with the elastic membrane.

13. The pump of claim 1 in which the inlet flap portion and/or the outlet flap portion each comprises a displaceable portion of the elastic membrane incompletely surrounded by a cut in the membrane such that the displaceable portion can be flexed out of the plane of the membrane about a hinge portion of the membrane.

14. The pump of claim 13 in which the displaceable portion incompletely surrounded by the cut has a diameter greater than the diameter of a port or opening in the plate against which the displaceable portion seats and smaller than the diameter of a chamber in the plate into which it can be resiliently displaced.

15. The pump of claim 1 in which the two plates include a snap fit or friction fit connection mechanism for quick assembly of the pump with the elastic membrane held between the plates.

16. The pump of claim 1 in which the elastic membrane comprises an injection moulded membrane.

17. The pump of claim 7 in which the pressure differential required to open the control valve exceeds a pressure differential required to open the outlet valve.

18. The pump of claim 1 in which the outlet flap portion defines a component of an outlet valve comprising a control valve, the flap portion defining an asymmetric valve component adjacent the outlet port.

19. A fuel cartridge having a first reactant in a first chamber, the fuel cartridge being configured to pump first reactant fluid from the first chamber to a second reactant to thereby generate fuel, using the pump of any preceding claim.