Pump

Abstract

A pump that has a cavity (13) in which is located a flexible membrane (14). An inlet (24) opens into the cavity (13) and is associated with a valve (27). A valve (28) is likewise provided in an outlet (25). Also opening into cavity (13) is a port (22) to which means for applying negative and positive pressures can be connected whereby the flexible membrane (14) can be moved to its two states corresponding to completion of inlet and exhaust of a pumping cycle.

Description

BACKGROUND TO THE INVENTION

[0001] This invention relates to a pump. More particularly the present invention relates to a membrane pump.

[0002] Pumps, which incorporate a flexible element to achieve the pumping action, are known. For example, the flexible element can be in the form of a deformable tube. A pump of this type is described in our international patent specifications WO 99/01687 and WO 02/18790.

[0003] In WO 02/18790 there is described a pneumatic pinch mechanism for a deformable tube and, in particular, the mechanism when applied to the pump. The mechanism includes a piston movably located within a chamber with vent means so that at some point during a movement of the piston between the first and second positions, a pressure equalisation occurs within the chamber. Consequently, as the piston moves toward the first position a pressure increase occurs which can be used to deform the deformable tube. When the piston moves toward the second position, a negative pressure is created which can be used to return the deformable tube from its deformed configuration.

[0004] The pump has proved successful, but as with deformable tube pumps, the deformable tube can require regular replacement. This is generally due to the repeated closing and release of the tube leading to localised wear or fatigue in the tube, which can ultimately lead to the tube rupturing.

[0005] A further disadvantage with such pumps is that it is often difficult or not possible to produce a deformable tube (having the necessary characteristics of being able to deform and rebound or be returned to its non-deformed state) from a material, which is particularly suited for handling the materials intended to flow through the pump.

[0006] A membrane pump therefore provides an advantage that the membrane can be formed from a material, which has a wide range of applications, and indeed materials which are required in some applications, but which cannot be formed or economically formed into replaceable deformable tubes for use in pumps having cyclic deforming of the tube. However, membrane pumps to date are of constructions, which still give rise to mechanical stress in the diaphragm, thereby requiring regular replacement of the diaphragm. Also, many known diaphragm pumps fall short in performance, especially in achievement of full removal of fluid from the pump chamber on the exhaust stroke and full uptake on the inlet stroke.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to provide a membrane pump, which is of a construction resulting in reduction in mechanical stress in the membrane, thereby leading to longer membrane life.

[0008] It is a further object of the present invention to provide a membrane pump of a construction, which enables full removal of fluid on the exhaust stroke and fuller uptake on the inlet stroke during operation of the pump.

[0009] Broadly according to one aspect of the invention there is provided a pump including a cavity with an inlet port and an outlet port opening into and from the cavity, a flexible membrane located within the chamber and arranged to be bi-stable in two states corresponding to completion of inlet and exhaust of a pumping cycle.

[0010] Preferably the flexible membrane is mounted in the cavity with a preset whereby the membrane adopts one of the stable states.

[0011] The membrane is preferably formed from an elastomeric material which can be in sheet form.

[0012] In a preferred form the membrane is clamped between first and second housing sections, each section having a cavity section such that when the housing sections are assembled to form a housing, said cavity is formed.

[0013] The cavity is, in the preferred form, located in a housing, the cavity being connectable to a source or sources of negative and positive pressure and means to cyclically apply the positive and negative pressures to the cavity to cause the membrane to move between the stable states.

[0014] In a preferred form the first and section housing sections configured to form said cavity when the housing sections are joined together, clamp the membrane about a peripheral margin thereof.

[0015] The first housing section can include a recess into which the membrane is located, the peripheral dimensions of the membrane being greater than those of the recess whereby compressive forces are set up in the membrane when it is installed in the recess.

[0016] The second housing section can include a protruding portion which engages in the recess, when the first and second housing sections are combined together, to cause the membrane to be clamped in place.

[0017] Preferably there is a third housing section coupled to the second housing section, said third housing section including means for facilitating connection of inlet and outlet conduits for pumpable material.

[0018] In a preferred form the second and third housing sections include inlet and outlet openings and means for locating therein a valve element. The valve element can be a disk of flexible material.

[0019] Preferably the cavity is elongate and of curved cross-section, a port via which the source(s) of positive and negative pressure are connectable opens into the cavity.

[0020] The ends of the elongate cavity are preferably complex curved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the following more detailed description of the invention according to one preferred embodiment, reference will be made to the accompanying drawings in which:

[0022] FIG. 1 is a longitudinal cross-section through the pump,

[0023] FIG. 2 is an exploded view in cross-section of the pump as shown in FIG. 1,

[0024] FIG. 3 is a transverse cross-sectional view taken between the inlet and outlet ports but showing only two sections of the pump body,

[0025] FIG. 4 is a perspective view of one housing section of the pump,

[0026] FIG. 5 is a schematic view of the pump on an exhaust cycle,

[0027] FIG. 6 is a view similar to FIG. 5 but of the inlet cycle, and

[0028] FIG. 7 is a cross-sectional view of a second embodiment which incorporates a different form of control mechanism.

DETAILS DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0029] Referring firstly to FIGS. 1-3, the pump 10 is, according to a preferred embodiment, formed of two housing sections 11 and 12. When these are assembled together they define an internal pump cavity 13. Clamped between the housing sections 11 and 12, as will hereinafter be described, is a membrane 14 which is made from a suitable flexible material.

[0030] In the preferred form of the invention, the cavity 13 is elongate and, as shown in FIG. 4, each end 15 is complex curved. In cross-section as shown in FIG. 1, each end is also curved as indicated at 15. Furthermore, in transverse cross-section as shown in FIG. 3, the cavity 13 is also of curved cross-section.

[0031] Housing section 11 incorporates a rebate 16, which effectively results in an upstand or projecting portion 17. Thus, the cavity section 13a is effectively located, at least in part, in the resultant upstanding portion 17.

[0032] The other housing section 12 has a recessed portion 18 with cavity section 13b extending away from the floor of the recess 18. Thus, when the two housing sections 11 and 12 are brought together the projecting portion 17 engages snugly within recess 18. However, the arrangement is such that surface 20 of projecting portion 17, terminates a distance from the floor 19 of recess 18. In the preferred form of the invention, this distance D (see FIG. 1) is less than the thickness of the membrane 14. The reason for this gap D will hereinafter become apparent.

[0033] The membrane 14 is, in the preferred form of the invention, cut from sheet material. The material is elastomeric and of a type which is compatible with the material, that is intended to be pumped through the pump 10. For example, if the material to be pumped through the pump 10 is corrosive, then the membrane material is selected such as to be able to withstand the corrosive nature of the fluid. By way of further example, the membrane is selected from a food grade material in the event that the pump is to handle a liquid foodstuff.

[0034] The various types of materials and applications to which a pump of this type can be put are well known to those skilled in the art. Therefore further description herein is not necessary for the purposes of describing the construction and operation of the pump according to the invention.

[0035] According to the invention, the membrane 14 is cut in a shape and to a size, which enables it to be snugly fitted into the recess 18. However, the overall peripheral dimensions of the membrane 14 are greater than the peripheral dimensions of the sidewall 21 of the recess 18. Thus, when the membrane 14 is placed into the recess 18 compressive forces are set up in the membrane due to what is effectively an interference fit of the membrane 14 into the recess 18. This therefore causes membrane 14 to deform from its flat state into a state, which essentially conforms with the complex curved shape of the cavity section 13b. Effectively, the membrane 14 is mounted with a preset.

[0036] However, when the housing section 11 is combined with housing section 12 (the membrane 14 being in place in recess 18) the fact that distance D is less than the thickness of the membrane 14 causes the peripheral edge margin portion of the membrane 14 to be sandwiched and clamped between opposing surfaces 19 and 20. This clamping force provides yet further compressive forces in the membrane, which causes the membrane to even more closely adapt into the shape of the cavity section 13b. Thus, in effect the membrane 14 is in contact with, or located closely adjacent to the overall surface of the cavity section 13b.

[0037] A port 22 is formed in the housing section 12 and opens into the cavity section 13b. This port 22 can be offset toward one end of the cavity 13, as shown in the drawings, or else it can be located midway in the length of the cavity 13.

[0038] In one form of the invention, a narrow groove 22a can be formed in the wall surface of the cavity section 13b and extend along the length of the cavity 13 either side of from the port 22. Also a similar narrow groove (not shown) can be formed in cavity 13b. The effect of the narrow groove(s) is to prevent the pump from "choking" when the membrane approaches contact with the surface of the cavity. Such contact could prevent fluid flow from occurring and thereby result in the cavity not fully filling or exhausting. The narrow groove ensures that flow occurs right down to when the membrane comes into full overall contact with the cavity surface.

[0039] At each end of the cavity section 13a is a port, which opens from the cavity 13 to the outer surface 23 of housing section 11. Port 24 functions as an inlet port while port 25 functions as an outlet or exhaust port. Each of inlet ports 24 and exhaust port 25 can, as shown, be made up by a plurality of separate passages 24a and 25a respectively. A recess 26 is formed in the surface 23 of housing section 11 and into this is engaged a disk of flexible material which forms valve element 27. Likewise, a valve element 28 in the form of a disk of flexible material is provided in the exhaust valve 25 but it locates in a recess 29 in cover 30.

[0040] Cover 30 has connecting pieces 31 and 32 (e.g. in the form of annular walls or turrets) which respectively provide connections for an inlet line (not shown) to inlet valve 24 and an outlet or exhaust line (also not shown) from exhaust valve 25.

[0041] The arrangement of the membrane 14 in the cavity 13 as described above, results in the membrane 14 being bi-stable. One stable position of the membrane 14 is shown in full detail in FIG. 1 while the other stable position is shown in dotted detail. Thus, in the first stable position the membrane 14 is in the cavity section 13b and when in the second stable position the membrane 14 is located in the cavity section 13a. In effect therefore, the membrane 14 adopts a stable position in either a position which conforms with completion of intake of fluid through inlet valve 24 (i.e. the position shown in the drawings) and a full or completed exhaust position.

[0042] The membrane 14 is moved between its two stable positions by application of negative P1 and positive P2 pressures applied to the cavity 13b through port 22. Consequently with the pump in the configuration shown in FIG. 1 and inlet and outlet conduits or lines attached to connectors 31 and 32 a positive pressure P2 (see FIG. 5) applied through port 22 will force the membrane 14 into an opposite stable position. In this "stroke" of the membrane 14, the inlet valve 24 is forced closed while the outlet valve 25 is forced open and any fluid within the cavity 13 i.e. to that side of the membrane opposite to that which faces port 22, is exhausted through the outlet valve 25.

[0043] Upon this "stroke" having been completed a negative pressure P1 applied via port 22 (see FIG. 6) causes the membrane 14 to return to the position shown in FIG. 1 which also causes the exhaust valve 25 to close but the inlet valve 24 to open and enable fluid in the inlet line to be drawn into cavity 13. The cavity 13 thus fills with the fluid ready to be exhausted through the outlet valve 25 upon the next cycle occurring when membrane 14 moves back into cavity section 13a under positive pressure P2.

[0044] The means for applying negative and positive pressures can take on many forms as will be apparent to the person skilled in the art. The means could comprise, for example, sources of positive and negative pressure, which via suitable valves can be coupled to the port 22.

[0045] Examples of mechanisms we have developed for applying the positive and negative pressures via port 22 are shown in FIGS. 1 and 7.

[0046] As shown in FIG. 1, there is a pneumatic operator 33 that has a body 34 which defines a chamber 35 in which a piston 36 is reciprocally mounted. A piston rod 37 is pivotally connected via pivot 38 to the piston 36. This piston rod 37 is pivotally connected by pivot 39 at its other end to a rotating drive member 40. The drive member 40 is connected to a drive means (not shown) which can be in the form of an electric motor or some other form of motive power.

[0047] A port 41 in the end wall 42 of the body 34 is in communication with port 22. As shown in FIG. 1 the body 34 is in close proximity to the pump 10 but it will be appreciated by those skilled in the art that the pneumatic operator 33 could be located quite some distance away from the pump 10 and connected by a conduit extending between ports 22 and 41.

[0048] A recess 43 is formed in the inside surface of the side wall 34a of body 34. The recess is located adjacent the end of wall 42.

[0049] At a position in the length of the side wall 34a of the body 34 there is a port 43a which opens to atmosphere. As illustrated, the port 43a is shown in one preferred position where it is adjacent the inner end of the piston 36 when the piston is at its full stroke away from end wall 42 of body 34. Thus, once the piston has moved past the port 43a (i.e. into the position of FIG. 1) the chamber 35 is fully vented to atmosphere. The position of port 43a can be varied dependent on use requirements that may require venting before the full stroke of piston 36 has been completed.

[0050] Consequently, when the piston 36 advances toward end wall 42 the air in chamber 35 becomes compressed and the resultant positive pressure P2 works on the membrane 14 to force it into cavity section 13a. However, when the piston 36 has completed its stroke toward wall 42 the piston sealing ring 36a is positioned within the area of the recess 43 whereby air can flow past the sealing ring 36a and exhaust through the clearance between the piston 36 and surface of wall 36a.

[0051] Upon its reverse stroke commencing the piston 36 moves so that sealing ring 36a moves away from recess 43 and once again seals against the entire peripheral surface of wall 36a. Consequently, the movement of the piston creates negative pressure P1 until the port 43a opens to vent the chamber 35 to atmosphere and hence complete the pumping cycle.

[0052] An alternative arrangement is shown in FIG. 7.

[0053] A port 43' in the wall 34a is connected to a conduit 44 which is, in turn, connected to a vent housing 45. One wall of the vent housing 45 has a vent opening 49 which opens into a chamber 50 in which a pin 51 is moveably located. The pin 51 is therefore moveable between the position where conduit 44 is isolated from vent 49 to a position where the vent 49 is connected to conduit 44.

[0054] Mounted with a periphery of the driving member 40 and projecting there from is a pair of curved or shaped (e.g. ramped) projections 52 and 53. Consequently, as the rotating member 40 rotates, a projection 52 or 53 comes into contact pin 51 which forces the pin 51 inwardly (relative to the housing) thereby connecting or disconnecting the vent 49 from the conduit 44.

[0055] This action causes the chamber 35 to vent to atmosphere (via vent 49) for the period of time that the pin 51 fails to seal closed the conduit 44. In the preferred form of the invention the pin 51 is biased by suitable biasing means (not shown) such as a spring or the like into a position where the vent 49 is closed i.e. isolated from conduit 44.

[0056] As a consequence, continued movement of the piston 36 creates a positive pressure build up which via port 22 forces the membrane 14 from the position shown in FIG. 7 to its other stable position in cavity section 13a. Material resident in the cavity 13 is thus forced out through the exhaust port 25.

[0057] As the piston 36 moves back along the chamber 35 from the second position the vent port 49 will still be closed. This will continue to be the situation until the engagement projection 52 comes into contact with pin 51 to effectively open the vent port 49. As a result, the vent port 49 once again vents the chamber 35 to atmosphere. After the vent 49 is closed from conduit 44 by movement of the pin 51 and as a result of the pin clearing the projection 52, the continued movement of the piston 36 back to its first position will create a negative pressure.

[0058] This negative pressure build up will cause the membrane 14 to move back to the position shown in FIG. 7 thereby creating a negative pressure within the chamber 13 which draws pumpable medium on the inlet 24 to be drawn through the inlet valve 24 and into the cavity 13. This inflow will continue until the membrane 14 is fully back into its position shown in FIG. 7.

[0059] Preferably the point and the movement of the piston 36 where contact between the pin 51 and projections 53 respectively occurs is adjustable. According to the preferred form of the invention, projections 52 and 53 can be adjustable in position on the periphery of the driving member or rotor 40 so that, for example, the period during which the piston creates a positive pressure could be less. This would result in the time that the membrane is under negative pressure to be greater than the period that it is under positive pressure.

[0060] The bi-stable flexible membrane 14 effectively has a small amount of travel between its two states. It is not mechanically connected to any drive thereby giving the membrane free movement in the cavity 13. The cavity shape is round rectangular and its contoured to fit the bi-stable shape of the membrane. Consequently, the cavity supports the diaphragm over its full surface when the diaphragm is in a so-called stable state. The membrane is therefore subject to uniform pressure not only when in the stable states but during the transition between the states as it is supported on both surfaces by the incoming or outgoing pumpable medium and the positive or negative pressure applied across the whole membrane surface via port 22.

[0061] It is believed that the bi-stable nature of the membrane, the cavity shape and contour, as well as the uniform pressure to which the membrane is subjected will lead to a significant reduction in mechanical stress on the membrane. This will therefore equate to longer membrane life. Furthermore, during operation of the pump there will be full removal of fluid on the exhaust stroke and full uptake on the inlet stroke as the membrane 14 moves fully from contact and support within the two sections of the chamber.

[0062] The pump therefore provides maximum efficiency and good linear flow characteristics, the latter being more critical as viscosity of the pumpable medium increases. The outlet pressure will be governed by the drive pressure therefore no need for pressure limiting. Suction (lift) is governed by the negative pressure. There is thus consistent through put over a wide range of drive pressures.

[0063] The valves 24 and 25 are located at the half round extremities of the cavity and in close proximity to the cavity. This proximity of the valves to the cavity thus minimises voids thereby giving optimum dry prime and compression ratio.

[0064] The pump arrangement is such that only low inertia needs to be overcome in order to drive the membrane. The valves are progressively closed and finally close before full exhaust or intake. This means that the last thing to occur as the membrane 14 reaches its stable position is movement of the valves into a closed position or opening is the first thing to occur upon the membrane 14 moving from a stable position.

[0065] The invention as described herein is by way of example only and it will be appreciated by those skilled in the art that other embodiments incorporating the invention are possible.

Claims

1. (canceled)

2. (canceled)

3. A pump as claimed in claim 19 wherein the membrane is formed from an elastomeric material.

4. A pump as claimed in claim 3 wherein the membrane is formed from elastomeric sheet material.

5. A pump as claimed in claims 19 wherein the membrane is damped between first and second sections, of the housing each housing section with one of the opposing surfaces having a cavity section such that when the housing sections are assembled to form the housing, the cavity with opposing surfaces is formed.

6. A pump as claimed in claim 19 wherein a pressure port opens into said cavity, said pressure port being connectable to a source or sources of positive and negative pressures.

7. A pump as claimed in claim 6 further including a device to cyclically apply the positive and negative pressures to the cavity to cause the membrane to move between the stable states.

8. (canceled)

9. A pump as claimed in claim 5 wherein the housing sections are joined together and to clamp the membrane about a peripheral margin thereof.

10. A pump as claimed in claim 5 wherein the first housing section includes a recess into which the membrane is located, the peripheral dimensions of the membrane being greater than those of the recess whereby compressive forces are set up in the membrane when it is installed in the recess to thereby create the preset.

11. A pump as claimed in claim 6 wherein the second housing section includes a protruding portion which engages in the recess when the first and second housing sections are combined together, to cause the membrane to be clamped in place.

12. A pump as claimed in claim 19 further including a third housing section coupled to the second housing section, said third housing section including means for facilitating connection of inlet and outlet conduits for pumpable material.

13. A pump as claimed in claim 12 wherein the second and third housing sections include inlet and outlet openings and means for locating therein a valve element.

14. A pump as claimed in claim 13 wherein the valve element is a disk of flexible material.

15. A pump as claimed in claim 6 wherein the cavity is elongate and the pressure port is offset in the length of the cavity.

16. A pump as claimed in claims 7 wherein the cavity is elongate and of curved cross-section.

17. A pump as claimed in claim 15 or 16 wherein the ends of the elongate cavity are complex curved.

18. (canceled)

19. a pump including a housing, a cavity with opposing surfaces, an inlet port opening into the cavity, an outlet port opening from the cavity, a pressure port connected to the cavity, a flexible membrane located within the cavity, the flexible membrane being mounted within the housing and a pre-set is applied to the flexible membrane such that the membrane adopts a first stable state in contact with one of the opposing surfaces of the cavity and can be caused to invert into a second stable state by the application of pressure to the cavity via the pressure port, the bi-stable membrane thereby being movable between the first and second stable states corresponding to completion of inlet and exhaust of a pumping cycle.

20. A pump as claimed in claim 7 wherein the clamping of the membrane creates further compressive forces in the membrane.