GB2575829A

GB2575829A - Fluid pump assembly

Info

Publication number: GB2575829A
Application number: GB1812061.8A
Authority: GB
Inventors: Hatfield Stuart
Original assignee: TTP Ventus Ltd
Current assignee: TTP Ventus Ltd
Priority date: 2018-07-24
Filing date: 2018-07-24
Publication date: 2020-01-29
Anticipated expiration: 2038-07-24
Also published as: GB2575829B; GB201812061D0

Abstract

A fluid pump assembly, a body of a fluid pump assembly and a kit of parts is disclosed. The pump assembly comprises first and second body part. The pump further comprises an actuator, a nodal hole, and a valve located in an aperture; each being comprised by one of the first and second body portions. An interior cavity is defined by a first and second end wall comprised by the body components. A side wall connects the end walls. One of the body parts is separable from the assembly so that it can be replaced by a similar component. The detached component can be disposed of, with the other part being reused. An embodiment of the invention relates to an acoustic resonance pump. The disclosure also extends to a fluid pump assembly with a removable valve attached to an aperture.

Description

FLUID PUMP ASSEMBLY

BACKGROUND OF THE INVENTION

The present invention relates to a fluid pump assembly, in particular a fluid pump assembly comprising first and second body parts which are each separable from the assembly such as to be replaceable.

As a wide range of markets trend towards reduced size, highly integrated, compact and convenient products, there is a strong requirement for increasingly small, discrete fluid pumps capable of providing high pump performance. In some applications, the ability to accurately control fluid pressures and flows with low pulsatility is important.

A large number of the miniature fluid pumps in the known art are displacement pumps, i.e. pumps in which the volume of the pumping chamber is made smaller in order to compress and expel fluids through an outlet valve and is made larger so as to draw fluid in through an inlet valve. Whilst the use of piezo-driven displacement pumps has enabled small devices, the pump performance is limited by the small positive displacements achieved by the piezo diaphragms, and the low operation frequencies used.

An alternative method which can be used to achieve fluid pumping is use of acoustic resonance. This can be achieved using a long cylindrical cavity with an acoustic driver at one end, which drives a longitudinal acoustic standing wave. In such a cylindrical cavity, the acoustic pressure oscillation has limited amplitude. Varying cross-section cavities, such as cone, horn-cone, and bulb have been used to achieve higher amplitude pressure oscillations, thereby significantly increasing the pumping effect. In such higher amplitude waves, non-linear mechanisms which result in energy dissipation are suppressed by careful cavity design. Until recently, high amplitude acoustic resonance has not been employed within disc-shaped cavities in which radial pressure oscillations are excited. International Patent Application No. PCT/GB2006/001487, published as WO 2006/111775 (the ‘487 Application) and incorporated herein by reference, discloses a pump having a substantially disc-shaped cavity with a high aspect ratio, i.e. the ratio of the radius of the cavity to the height of the cavity.

The acoustic resonance pump described in the ‘487 Application operates on a different physical principle to the displacement pumps in the related art. In acoustic resonance pumps there exists, in operation, an acoustic standing wave within the pump cavity such that the fluid is compressed within one part of the cavity while the fluid is simultaneously expanded in another part of the cavity. In contrast to a conventional displacement pump, an acoustic resonance pump does not require a change in the cavity volume in order to achieve pumping operation. Instead, its design is adapted to efficiently create, maintain, and rectify the acoustic pressure oscillations within the cavity.

Turning to its design and operation, the ‘487 Application describes an acoustic resonance pump which has a substantially cylindrical shell comprising a substantially cylindrical side wall closed at each end by end walls, one or more of which is a driven end wall. The driven end wall is achieved with an actuator that causes an oscillatory motion of the end wall (“displacement oscillations”) in a direction substantially perpendicular to the end wall or substantially parallel to the longitudinal axis of the cylindrical cavity, referred to as “axial oscillations” of the driven end wall. The axial oscillations of the driven end wall generate substantially proportional “pressure oscillations” of fluid within the cavity creating a radial pressure distribution approximating that of a Bessel function of the first kind as described in the ‘487 Application; such pressure oscillations are referred to as “acoustic standing waves” within the cavity.

The pump disclosed in the ‘487 Application comprises of one or more valves for controlling the flow of fluid through the pump and, more specifically, valves being capable of operating at high frequencies, as it is preferable to operate the pump at frequencies beyond the range of human hearing. The combination of the high amplitude pressure oscillations provided by the acoustic resonance pump and high operational frequency valve enables a high pump performance within a small device size.

As a result of the high frequency operation of the pump disclosed in the ‘487 Application, the pump has strong benefits in applications where smooth, highly controllable flow are required, such as microfluidics, point-of-care instrumentation and gas sensing. This kind of pump typically forms an integral part of a product and its integration into the product may be complex. Furthermore the product is typically disposed of after use, which is wasteful of the pump and so can significantly increase product cost. There is therefore a need for a fluid pump, which may provide the kind of benefits provided by the pump disclosed in the ‘487 Application but which lessens the cost and/or complexity of the product which includes the pump.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a fluid pump assembly comprising: first and second body parts; an actuator, a nodal hole, an aperture and a valve which is located in the aperture, each being comprised by one of the first and second body parts; and an interior cavity which is defined by a first end wall comprised by the first body part, a second end wall comprised by the second body part, and a side wall which connects the first and second end walls, wherein at least one of the first and second body parts (e.g. including the actuator, nodal hole, and/or aperture and valve comprised thereby) is separable from the assembly such as to be replaceable in the assembly by a similar body part.

In other words, the fluid pump assembly described herein comprises first and second body parts connected by a (preferably continuous) side wall to define an interior cavity between the first and second body parts. One of said first and second body parts comprises an actuator, one of said first and second body parts comprises a nodal hole, and one of said first and second body parts comprises a valve located in an aperture, such that each of said first and second body parts comprises at least one of said actuator, nodal hole and valve (located in an aperture). At least one of the first and second body parts is separable from the assembly such that it can be substituted in the assembly by a similar (e.g. replacement) body part.

According to the invention, either one of the first and second body parts (and the components thereof) can be replaced in the pump assembly, such that the other one of the first and second body parts (and the components thereof) can be reused. Thus one of the first and second body parts is a disposable part, while the other one of the first and second body parts is a reusable part which can be reused with a succession of different disposable parts of the pump assembly. Thus the product which contains the pump can be used over and over again, with only a relatively inexpensive part of the pump having to be disposed of each time. This reuse capability represents a significant cost saving.

The cavity may be cylindrical. The cylindrical cavity may have a radius, a, and a height, h, the ratio a/h being greater than about 1.2.

The first end wall may comprise the actuator and the second end wall may comprise the nodal hole and the aperture and valve.

The fluid pump assembly may comprise a membrane which extends across the cavity such that in use the actuator is isolated from a fluid contained in the cavity by the membrane. The provision of the membrane means that the fluid path may be contained entirely within the second body part, such that the first body part is isolated from the fluid. The ability to replace the second body part including the fluid flow path has clear advantages with regard to sterility and avoidance of contamination or degradation, as well as simple convenience. Moreover the separation of the fluid path from the actuator (and other components) reduces the complexity of the device.

The second body part may comprise the membrane. The actuator may be spaced apart from the membrane. The actuator may be in contact with the membrane. The first body part may comprise at least one biasing element for holding the actuator in contact with the membrane.

The fluid pump assembly may comprise an isolator which attaches the actuator to the first or second body part or the side wall.

One of the first and second body parts may comprise the side wall, the side wall being removably attached to the other one of the first and second body parts. The fluid pump assembly may comprise an intermediate body part which comprises the side wall, the side wall being removably attached to each one of the first and second body parts.

The removable attachment may comprise a mechanical fastening, magnetic or electrostatic force, adhesive, or vacuum.

One or both of the first and second body parts may comprise plastics, metal or metal alloy, glass, or semi-conductor material.

The fluid pump assembly may comprise: a third body part; and a second interior cavity which is defined by a third end wall comprised by the third body part, the second end wall, and the side wall which connects the second and third end walls.

In use, the cavity may contain a fluid and the actuator may be operable to cause oscillatory motion of one or both of the first and second end walls, in a direction substantially perpendicular to the plane of the first and second end walls, such that the axial oscillations of the first and second end walls drive radial oscillations of fluid pressure in the cavity.

According to another aspect of the invention, there is provided a kit of parts for a fluid pump assembly as described above, the kit of parts comprising: discrete first and second body parts; and an actuator, a nodal hole, an aperture and a valve which is located in the aperture, each being comprised by one of the first and second body parts.

The at least one of the first and second body parts may comprise attachment means for removably attaching the body part in the assembly.

According to another aspect of the invention, there is provided a body part for a fluid pump assembly as described above, the body part comprising: one or more of an actuator, a nodal hole, an aperture and a valve which is located in the aperture; and attachment means for removably attaching the body part to another body part of the fluid pump assembly.

According to another aspect of the invention, there is provided a fluid pump assembly comprising a pump body and a valve, wherein the valve is removably attached to an aperture in the pump body such as to be replaceable in the assembly by a similar valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example, with reference to the accompanying figures in which:

Figures 1a-2b show simplified sectional representations of separable fluid pumps according to embodiments of the invention;

Figures 3a-3c show details of the construction of a separable fluid pump according to Figure 2a;

Figures 4a-4c show details of an alternative construction of a separable fluid pump according to Figure 2a; and

Figures 5a and 5b relate to an arrangement of a fluid pump comprising a replaceable valve.

DETAILED DISCUSSION

Referring to Figure 1a, a separable fluid pump comprises a first body part and a second body part which are removably attachable to each other. The first body part comprises an actuator. In this exemplary embodiment the actuator comprises a piezoelectric disc. Alternatively the actuator may comprise a magnetostrictive device. The actuator may be driven by a solenoid. The actuator may be an electrostatically driven plate.

In this embodiment the first body part further comprises a cavity wall or side wall, and an isolator which joins the actuator to the side wall. The isolator may comprise a ‘skirt’ of plastic, metal or other material. The isolator may be an extension of a substrate which allows relatively undamped vibration of the actuator, e.g. spokes, or ‘sprung’ contacts. Alternatively the isolator may be a mechanical structure which clamps the actuator in place but allows relatively undamped motion. The isolator may incorporate electrical contacts. Alternatively the isolator may be omitted and the actuator joined directly to the side wall.

The second body part provides a fluid flow path. The fluid may be a liquid or a gas, or both. The second body part includes a nodal hole and an aperture in which a valve is installed. In the figure the nodal hole is shown as providing an outlet and the aperture as providing an inlet. Alternatively the nodal hole may provide an inlet and the aperture may provide an outlet. The valve may be a high frequency valve. Alternatively the valve may comprise a high frequency structure which is built directly into the body. Alternatively the valve and node may be replaced by a single split valve providing the inlet and outlet.

The first body part and/or the second body part may comprise plastics, metal or metal alloy, glass, or semi-conductor material. One or both of the first and second body parts may be of unitary construction.

The first body part and/or the second body part may comprise a single part (machined, fabricated (MEMs), etched, moulded, vacuum formed, or stamped). Alternatively the first body part and/or the second body part may comprise an assembly (laminated, assembled, or bonded).

When the first body part and the second body part are connected together in combination there exists, in the interior of the pump, a chamber or cavity. The cavity is bounded by: the actuator and isolator (of the first body part), which together form an upper end wall; the body of the second body part (including the nodal hole and valved aperture), which forms a lower end wall; and the side wall (of the first body part), which connects the upper and lower end walls (the end walls being parallel with each other).

In this embodiment the cavity is cylindrical. Alternatively the cavity may be a different shape, for example elliptical. The cavity may be frusto-conical.

The cylindrical cavity has a radius, a, and a height, h. In this embodiment the ratio a/h is greater than about 1.2. The ratio a/h may be greater than about 20. In some embodiments the value of h²/a is greater than 4x1 O'¹⁰ m.

In use the cavity is resonant. The motion of the actuator couples to the radial pressure mode of the cavity, creating a pressure anti-node at the centre of the cavity. The pressure anti-node causes a net flow of air through the valve, inducing airflow and/or pressure generation in first and second flow channels of the pump.

The first body part and the second body part may be aligned by, for example: mechanical keying features; aligning magnets; or optical alignment. Alternatively the first and second body parts may be connected together without the aid of such accurate means of alignment.

The first body part and the second body part may be removably connected using, for example: mechanical fixtures or fasteners within the first and second body parts; external fasteners (screw threads, snap fit, cages, bayonetted features, latches or clamps; magnetics (magnets in the first and second body parts and/or third clamping part); electrostatics; adhesive (glue, PSA, UV release adhesive); vacuum (externally or internally generated); or gravity under their own mass. The side wall and the second body part may seal against one another.

The fluid pump of Figure 1b is generally similar to the fluid pump of Figure 1a, except that the cavity wall or side wall is comprised in the second body part rather than in the first body part. More particularly, the second body part comprises a recess (in this embodiment a circular recess) such as to form the side wall. A floor of the recess comprises the nodal hole and aperture.

The fluid pump of Figure 1c is generally similar to the fluid pump of Figure 1a, except that the aperture and valve are comprised in the actuator (itself located in the first body part) rather than in the second body part.

The fluid pump of Figure 1d is generally similar to the fluid pump of Figure 1a, except that the side wall comprises a separate and discrete element which is removably attached to each of the first and second body parts. In other words, the side wall comprises an intermediate body part by which means the first and second body parts are indirectly attached to each other.

Turning now to Figure 2a, a separable fluid pump comprises a first body part and a second body part which are removably attachable to each other. The first body part comprises an actuator. In this exemplary embodiment the actuator comprises a piezoelectric disc. Alternatively the actuator may comprise a magnetostrictive device. The actuator may be driven by a solenoid. The actuator may be an electrostatically driven plate.

In this embodiment the first body part further comprises an isolator which joins the actuator to a cavity wall or side wall which is comprised by the second body part. The isolator may comprise a ‘skirt’ of plastic, metal or other material. The isolator may be an extension of a substrate which allows relatively undamped vibration of the actuator, e.g. spokes, or ‘sprung’ contacts. Alternatively the isolator may be a mechanical structure which clamps the actuator in place but allows relatively undamped motion. The isolator may incorporate electrical contacts. Alternatively the isolator may be omitted and the actuator joined directly to the side wall.

The second body part provides a fluid flow path and comprises a recess (which in this embodiment is a circular recess) such as to form the side wall. A floor of the recess includes a nodal hole and an aperture in which a valve is installed. In the figure the nodal hole is shown as providing an outlet and the aperture as providing an inlet. Alternatively the nodal hole may provide an inlet and the aperture may provide an outlet. The valve may be a high frequency valve.

Alternatively the valve may comprise a high frequency structure which is built directly into the second body part. Alternatively the valve and node may be replaced by a single split valve providing the inlet and outlet. The second body part further comprises a membrane which covers the circular recess.

The first body part and/or the second body part may comprise plastics, metal or metal alloy, glass, or semi-conductor material.

When the first body part and the second body part are connected together the actuator and the isolator are in direct contact with an upper surface of the membrane. The actuator and the isolator extend laterally across the membrane, such as to cover the majority (substantially all) of the upper surface of the membrane. In this state there exists, in the interior of the pump, a chamber or cavity. The cavity is bounded by: the (lower surface of the) membrane, which forms an upper end wall of the second body part; the body of the second body part (including the nodal hole and valved aperture), which forms a lower end wall; and the side wall (of the second body part), which connects the upper and lower end walls (the end walls being parallel with each other).

The cylindrical cavity has a radius, a, and a height, h. In this embodiment the ratio a/h is greater than about 1.2. The ratio a/h may be greater than about 20. In some embodiments the value of h²/a is greater than 4x1 O’¹⁰ m.

In use the cavity is resonant. The membrane moves with a mode shape substantially similar to that of the actuator. The motion of the membrane couples to the radial pressure mode of the cavity, creating a pressure anti-node at the centre of the cavity. The pressure anti-node causes a net flow of air through the valve, inducing air flow and/or pressure generation in first and second flow channels of the pump.

The provision of the fluid-blocking membrane advantageously allows for the first body part to be fully isolated from the fluid path which is contained in the second body part.

The membrane may be formed of plastic, rubber, thin glass, or metal. The membrane and actuator motion may be matched by joining them by, for example: compression onto a taut membrane; electrostatics; vacuum; magnetics; adhesive (PSA, UV release adhesive, etc); mechanical joining features; or temporary bonding methods (e.g. heat bonding). The membrane may be joined to the second body part by, for example: lamination; adhesive; mechanical clamping; electrostatics; welding; or solvent bonding.

The fluid pump of Figure 2b is generally similar to the fluid pump of Figure 2a, except that the cavity wall or side wall is comprised in the first body part as well as the second body part. Thus, when the first body part and the second body part are connected together, the actuator and isolator are axially spaced from the membrane. Accordingly there is provided a second cylindrical cavity, which is bounded by: the actuator and isolator, which together form an upper end wall of the first body part; the (upper surface of the) membrane, which forms a lower end wall; and the side wall (of the first body part) which connects the upper and lower end walls (the end walls being parallel with each other).

In use the first (lower) and second (upper) cavities are resonant. The motion of the actuator couples to the radial pressure mode of the second cavity. The membrane transmits energy to the radial pressure mode of the first cavity. The pressure anti-node in the first cavity causes a net flow of air through the valve, inducing airflow and/or pressure generation in first and second flow channels of the pump.

The membrane may be formed of a thin flexible material such as plastic, rubber, thin glass or metal. The membrane may be a mechanical structure designed to resonate with the appropriate frequency and mode shape. The membrane may be an air permeable barrier layer which allows the air pressure wave to transmit directly from the second cavity chamber to the first cavity chamber, but which prevents contamination from passing through, for example by use of a filter material or hydrophobic barrier.

Referring now to Figure 3a (which shows details of the construction of a first body part of a pump generally according to Figure 2a), the first body part comprises the actuator and the isolator. More specifically the actuator is mounted to the body by springs which bias the actuator away from the body (downwardly in the sense of Figure 3a). The actuator is electrically connected to drive electronics by two electrical contacts to provide pump drive and control. The first body part has location features to axially locate the first body part to the second body part. Magnets are embedded in the first body part to join the first body part to the second body part.

Referring also to Figure 3b (which shows details of the construction of a second body part of a pump generally according to Figure 2a), the second body part is a moulding which comprises the first and second flow channels and also pneumatic connections. The valve is bonded into the aperture. The membrane comprises a lamination at the upper side of the second body part. The lower side of the second body part is also laminated so as to form a further, lower membrane which caps the flow channels. Magnets or magnetically permeable materials are embedded in the second body part for removably joining the second body part to the first body part.

Referring now to Figure 3c, the first body part and the second body part are connected together such that the location features axially locate the two body parts. The magnets in the first body part and the second body part join the body parts together. The actuator is biased against the membrane by the springs.

When driven by the drive electronics, the actuator moves with a velocity profile substantially similar to the mode shape of the acoustic cavity pressure. The membrane moves with substantially similar velocity profile to the actuator. The motion of the membrane couples to the radial pressure mode of the cavity, creating a pressure anti-node at the centre of the cavity. The pressure anti-node causes a net flow of air through the valve. Air is drawn from one pneumatic connection to the other.

Channels or features may be patterned in the actuator surface which contact with the membrane to prevent air bubbles between the membrane and the actuator when pressed together.

The springs (or other type of biasing elements) may contact the actuator at the nodal point of motion. The springs may be compliant to prevent noise (ringing of actuator). The electrical contacts may be wires, sprung contacts, or bonded flexible circuit. The first body part has a ‘back chamber’ behind the actuator which may be designed to be non-resonant to avoid damping of the actuator (shaping, surface finish, holes to relieve pressure).

Referring now to Figure 4a (which shows details of the construction of a first body part of a pump generally according to Figure 2a), the actuator is mounted to a support structure via the isolator. The actuator is electrically connected to drive electronics by a flexible circuit which is laminated onto the device. The first body part has sprung clipping connection features to axially locate the first body part to the second body part and removably attach the body parts together. The first body part comprises manifold elements for linking the pneumatic circuits of two of the second body parts.

Referring also to Figure 4b (which shows details of the construction of a second body part of a pump generally according to Figure 2a), the second body part is a moulding which comprises the first and second flow channels and also pneumatic connections. The valve is bonded into the aperture. The membrane comprises a lamination at the upper side of the second body part. The lower side of the second body part is also laminated so as to form a further, lower membrane which caps the flow channels.

Referring now to Figure 4c, two second body parts of the type described are provided. The first body part and the two second body parts are removably connected together such that the first body part is sandwiched between the two second body parts and the two second body parts have opposite valve orientations. The clip connection features axially locate the first body part and the second body parts. The clip connection features in the disposable parts clip onto the moulded connection feature of the first body part to removably join the body parts together. When so joined, the manifold element pierces the membrane in the region of the cross channel to join the two second body parts to each other. The actuator is biased against the membranes by the opposing forces of the two membranes.

When driven by the drive electronics, the actuator moves with a velocity profile substantially similar to the mode shape of the acoustic cavity pressure in the two cavities. The two membranes move with substantially similar velocity profile to the actuator. The motion of the two membranes couples to the radial pressure mode of the two cavities, creating a pressure anti-node at the centre of each cavity (180 degrees out of phase from one another). The pressure anti-node in the first cavity causes a net flow of air from the first pneumatic connection to the manifold element. The pressure anti-node in the second cavity causes a net flow of air from the manifold element to the second pneumatic connection. The combined flow and pressure in the two cavities in series provides a pressure doubling effect. A flow path is created which may be fully isolated from the first body part.

The second body parts may be combined in parallel rather than series to provide a flow doubling effect. The manifold element may be a separate component to allow the full second body part path to be removed from the first body part. The second body parts may be pneumatically separated to provide two pneumatically isolated pumps driven commonly. The support structure may be a PCB which comprises the drive electronics. While the first body part is shown in conjunction with two second body parts, alternatively just one second body part may be used with the first body part.

With regard to each of the above-described embodiments, the first body part (and the components thereof, i.e. the actuator, nodal hole, aperture, valve which is located in the aperture) may be removed from the pump assembly, discarded, and replaced (e.g. substituted) in the pump assembly with a new, similar first body part (including similar components). In this way the second body part (and the components thereof) may be reused. Thus the first body part (including its components) is disposable, while the second body part (including its components) is reusable. Alternatively, the second body part (and the components thereof, i.e. the actuator, nodal hole, aperture, valve which is located in the aperture) may be removed from the pump assembly, discarded, and replaced in the pump assembly with a new, similar second body part (including similar components). In this way the first body part (and the components thereof) may be reused. Thus the second body part (including its components) is disposable, while the first body part (including its components) is reusable.

It will be understood that each of the components (i.e. the actuator, nodal hole, aperture, valve which is located in the aperture) is comprised by one or other of the first and second body parts. As used herein, the term “comprised by” preferably connotes that the first or second body parts comprises (at least) one or more of said components. With regard to which of the components is comprised by which of the body parts, any combination is within the scope of the claimed invention, provided that each of the first and second body parts comprises at least one of the components. In other words, the first body part comprises one or more of said actuator, nodal hole, aperture and valve, and the second body part comprises the other one or more of said actuator, nodal hole, aperture and valve, such that all of said components are present in the assembly. One or both of the first and second body parts (including the actuator, nodal hole, and/or aperture and valve comprised thereby) is separable (removable) from the assembly such as to be replaceable in the assembly by a similar (structurally identical) body part including components (actuator, nodal hole, and/or aperture and valve) of the same type.

Referring now to Figure 5a, a valve is removable from a fluid pump assembly of the kind described above, such that the valve can be discarded and replaced in the assembly by a similar valve. That is, the valve is separable from (the aperture of) the pump body. Thus the valve is disposable while the remainder of the pump assembly is reusable. This effectively extends the life of the pump, since the valve may tend to wear at a faster rate than the other pump components.

The valve should be installed in a body part of the pump assembly in such a way as to facilitate convenient replacement. Also with regard to valve installation, the valve should be robust against pressure oscillation in the cavity and should support a pressure difference across the valve without back-leaks. In addition the valve should present a valve active area which is close to the cavity (i.e. not down a long tube of ‘dead’ volume).

Some suitable means of valve installation/connection are shown in Figure 5b. As can be seen, the valve may be clamped against a lip of the pump body using a screw thread. Or the valve may be held in the aperture of the body by a mechanical clip. Alternatively the valve may be secured in the aperture by means of an interference fit (i.e. a tight, friction fit) with the walls of the aperture (which may be compliant). Or the valve may be attached to the body at the aperture using PSA adhesive to provide a temporary bond. Alternatively one or both of the valve and pump body may comprise a magnet or magnetic material, such that the valve is held in the aperture by magnetic force. A large/wide valve may be provided which forms an entire end wall of the pump cavity, this valve being installed by any of the means described above.

It will be understood that the invention has been described in relation to its preferred embodiments and may be modified in many different ways without departing from the scope of the invention as defined by the accompanying claims.

Claims

1. A fluid pump assembly comprising:

first and second body parts;

an actuator, a nodal hole, an aperture and a valve which is located in the aperture, each being comprised by one of the first and second body parts; and an interior cavity which is defined by a first end wall comprised by the first body part, a second end wall comprised by the second body part, and a side wall which connects the first and second end walls, wherein at least one of the first and second body parts is separable from the assembly such as to be replaceable in the assembly by a similar body part.

2. A fluid pump assembly according to claim 1, wherein the cavity is cylindrical.

3. A fluid pump assembly according to claim 2, wherein the cylindrical cavity has a radius, a, and a height, h, the ratio a/h being greater than about 1.2.

4. A fluid pump assembly according to any preceding claim, wherein the first end wall comprises the actuator and the second end wall comprises the nodal hole and the aperture and valve.

5. A fluid pump assembly according to claim 4, comprising a membrane which extends across the cavity such that in use the actuator is isolated from a fluid contained in the cavity by the membrane.

6. A fluid pump assembly according to claim 5, wherein the second body part comprises the membrane.

7. A fluid pump assembly according to claim 5 or 6, wherein the actuator is spaced apart from the membrane.

8. A fluid pump assembly according to claim 5 or 6, wherein the actuator is in contact with the membrane.

9. A fluid pump assembly according to claim 8, wherein the first body part comprises at least one biasing element for holding the actuator in contact with the membrane.

10. A fluid pump assembly according to any preceding claim, comprising an isolator which attaches the actuator to the first or second body part or the side wall.

11. A fluid pump assembly according to any preceding claim, wherein one of the first and second body parts comprises the side wall, the side wall being removably attached to the other one of the first and second body parts.

12. A fluid pump assembly according to any one of claims 1 to 10, comprising an intermediate body part which comprises the side wall, the side wall being removably attached to each one of the first and second body parts.

13. A fluid pump assembly according to claim 11 or 12, wherein the removable attachment comprises a mechanical fastening, magnetic or electrostatic force, adhesive, or vacuum.

14. A fluid pump assembly according to any preceding claim, wherein one or both of the first and second body parts comprises plastics, metal or metal alloy, glass, or semi-conductor material.

15. A fluid pump assembly according to any preceding claim, comprising:

a third body part; and a second interior cavity which is defined by a third end wall comprised by the third body part, the second end wall, and the side wall which connects the second and third end walls.

16. A fluid pump assembly according to any preceding claim, wherein in use the cavity contains a fluid and the actuator is operable to cause oscillatory motion of one or both of the first and second end walls, in a direction substantially perpendicular to the plane of the first and second end walls, such that the axial oscillations of the first and second end walls drive radial oscillations of fluid pressure in the cavity.

17. A kit of parts for a fluid pump assembly according to any one of claims 1 to 16, comprising:

discrete first and second body parts; and an actuator, a nodal hole, an aperture and a valve which is located in the aperture, each being comprised by one of the first and second body parts.

18. A kit of parts according to claim 17, wherein at least one of the first and second body parts comprises attachment means for removably attaching the body part in the assembly.

19. A body part for a fluid pump assembly according to any one of claims 1 to 16, comprising:

one or more of an actuator, a nodal hole, an aperture and a valve which is located in the aperture; and attachment means for removably attaching the body part to another body part of the fluid pump assembly.

20. A fluid pump assembly comprising a pump body and a valve, wherein the valve is removably attached to an aperture in the pump body such as to be replaceable in the assembly by a similar valve.