WO2015193675A1

WO2015193675A1 - Dispensing pump with first and second membrane pumps

Info

Publication number: WO2015193675A1
Application number: PCT/GB2015/051788
Authority: WO
Inventors: Ronald Skinner
Original assignee: Brightwell Dispensers Limited
Priority date: 2014-06-20
Filing date: 2015-06-18
Publication date: 2015-12-23
Also published as: GB201411058D0; GB2529611B; GB2529611A

Abstract

A dispensing pump comprising a motor, a driveshaft rotatable by said motor in both a first direction and a second direction opposite to said first direction, a first membrane pump comprising a first operating plunger mounted to said driveshaft by a first coupling, and a second membrane pump comprising a second operating plunger mounted to said driveshaft by a second coupling, in which said first coupling and said second coupling each comprise a cam body which converts rotational movement of said driveshaft into reciprocal movement of said first operating plunger and second operating plunger respectively, in which said first coupling and said second coupling each comprise a clutch bearing which is only engaged by rotation of said driveshaft in said first direction and said second direction respectively.

Description

Dispensing Pump with First and Second Membrane Pumps

The present invention relates to a dispensing pump with first and second membrane pumps, for use particularly, but not exclusively, to dispense separate cleaning chemicals into washing machines and dishwashers and the like.

Domestic and industrial dishwashers and laundry washing machines use one or more different chemical substances to wash and rinse the objects placed in them. Such chemical substances can be detergents, soaps, rinse aids and so on, and are usually provided in a concentrated form to be diluted in water. In small domestic machines these chemical substances are placed in a tray or tank and are circulated into the washing system via internal plumbing. Each particular substance is circulated at pre-determined intervals according to a washing and rinsing cycle.

However, the quantity of chemical substance used is not usually well controlled, and the same amount is often provided each time, when different wash cycles actually require differing amounts. In addition, it is common to provide too much or too little chemical. These problems are exacerbated when the machines are industrial in size, and when large numbers of such machines are taken into consideration. It is common for a facility such as a hotel to have large numbers of washing machines. If all these machines are used incorrectly, or inefficiently, then very large quantities of chemical substances can be wasted, and introduced to the sewerage system and the greater environment unnecessarily.

Therefore, it is known to provide industrial washing machines with improved aftermarket chemical dispensing systems. Such systems comprise external, electronically programmable pumps provided with a source of chemical, often from a large container. The pumps are integrated into the machine's control system so they operate when the machine requires an input of chemical substance. These retro-fit systems provide improved control of chemical input, and can be used to provide various different chemicals at different times. The best systems can be precisely controlled and can be set up to operate in a large number of different ways. Any known kind of pump can be used in such systems, including peristaltic pumps and membrane pumps. Such pumps comprise an electric motor, a driveshaft rotatable by the motor, and a pumping arrangement which is mounted to the driveshaft. A coupling converts the rotational movement of the driveshaft into a pumping action. In the case of a peristaltic pump this is the rotatory movement of rollers, and in the case of a membrane pump this is the reciprocal movement of an operating plunger. Where numerous machines are in use there needs to be a separate motor and pumping arrangement for each chemical supplied to each machine, which adds to the cost and space taken up. Therefore, it is known to provide modular systems comprising motor housings to which numerous identical pumps can be releasably fitted to suit.

WO 90/13743 in the name of the applicant discloses a pump comprising a single motor with a driveshaft extending therefrom, and two pumps mounted to the driveshaft by couplings capable of transmitting torque in one direction only. As such, rotation of the driveshaft in one direction operates one pump, and rotation of the driveshaft in the opposite direction operates the other pump. The advantage is that one motor can be used to operate two different pumps, saving a motor, and decreasing size and costs. However, this prior art relates to the use of peristaltic pumps, which are axially very short, as they only comprise a set of radially mounted rollers working a radially mounted tube. As such, the configuration of adjacent pumps is small in size and therefore effective. The embedment described encloses the two peristaltic pumps within the same enclosure, immediately adjacent to one another. However, peristaltic pumps suffer from a number of drawbacks. In particular, the tubes wear out relatively quickly and require replacement, and there are a relatively large number of moving parts, which increases the risk of failure.

The present invention is intended to overcome some of the above problems.

Therefore, according to the present invention, a dispensing pump comprises a motor, a driveshaft rotatable by said motor in both a first direction and a second direction opposite to said first direction, a first membrane pump comprising a first operating plunger mounted to said driveshaft by a first coupling, and a second membrane pump comprising a second operating plunger mounted to said driveshaft by a second coupling, in which said first coupling and said second coupling each comprise a cam body which converts rotational movement of said driveshaft into reciprocal movement of said first operating plunger and second operating plunger respectively, in which said first coupling and said second coupling each comprise a clutch bearing which is only engaged by rotation of said driveshaft in said first direction and said second direction respectively.

Thus, the present invention provides a dispensing pump with one motor, which can operate two separate membrane pumps by rotating the driveshaft in opposite directions. Membrane pumps are simpler and longer lasting than peristaltic pumps, but their shape and configuration makes them inherently unsuitable for adjacent use on a single driveshaft. A membrane pump comprises a resilient membrane with a given radius, mounted for movement above a chamber which is axially much shorter than that radius. As such, membrane pump housings are generally flat and square, and when they are driven by a driveshaft they must be arranged parallel with the driveshaft, with the operating plunger extending at right angles to the driveshaft. In comparison, a peristaltic pump is mounted radially around the driveshaft, which is a much more compact and effective configuration.

It would be possible to stagger two membrane pumps mounted on the same driveshaft, with the housings arranged at different angles to the drive shaft, and with the membranes in different planes. This would allow for the operating plungers to be relatively close to one another on the drive shaft, and for the whole dispensing pump to be axially short. However, it also makes the membrane pumps operate differently to one another, as gravity has a different effect on each one, which is not an effective outcome. This is particularly the case if one pump were inverted in relation to the other.

Therefore, in a preferred embodiment the first and second membrane pumps can each comprise a membrane with a static perimeter, and they can be arranged with the static perimeter of their respective membranes in the same plane. Further, the first and second membrane pumps can each comprise a body which defines a pump chamber, and they can be arranged with their respective bodies alongside one another.

With this arrangement the two membrane pumps will operate in the same way, as gravity will have the same effect on both of them. However, it does make the dispensing pump axially large.

Preferably the dispensing pump can further comprise a motor housing from which the driveshaft projects, and a rear of the first membrane pump can be releasably attached to a front of the motor housing, with the first coupling releasably mounted to the driveshaft. Further, a rear of the second membrane pump can be releasably attached to a front of the first membrane pump, with the second coupling releasably mounted to said drive shaft.

Therefore, the first and second membrane pumps can be modular units which can be mounted to the motor housing to suit. The first and second membrane pumps can be identical, save for the orientation of the clutch bearing.

Due to the manner in which the first and second membrane pumps are arranged alongside one another the driveshaft must be relatively long in order to pass through the coupling of the second membrane pump. As such, the potential for any deviation in the performance of the driveshaft along its length is greater than it otherwise would be. If any such deviation is present, this will affect the performance of the second membrane pump.

In order to address this problem, the first and second membrane pumps can each comprise a cover which can be releasably mounted to their body, and which can enclose the first and second operating plungers respectively. The covers can each comprise a first support bearing provided in a first side thereof, which can be releasably mounted to the driveshaft, and a second support bearing provided in a second side thereof, which can also be releasably mounted to the driveshaft.

These support bearings can perform an important role in supporting and stabilising the driveshaft, to ensure that it provides a uniform performance along its length, so the first and second membrane pumps can be operated in the same way.

In a preferred embodiment the dispensing pump can comprise one or more further motors, each of which can comprise a further driveshaft rotatable thereby in both a first direction and a second direction opposite to the first direction. There can also be one or more further membrane pumps each comprising an operating plunger mounted to a further driveshaft by a coupling comprising a cam body which can convert rotational movement of that further driveshaft into reciprocal movement of that operating plunger, that coupling comprising a clutch bearing which is only engaged by rotation of that further driveshaft in said first direction or said second direction.

With this configuration the dispensing pump as a whole can operate four, six or more membrane pumps, which might be suitable in some installations.

As referred to above, it is possible to mount the first and second membrane pumps in a different configuration to that described above, despite the inherent drawbacks. It may be possible to effectively compensate for such drawbacks, for example by increasing the capacity of an inverted membrane pump so its operational performance was the same as a non-inverted membrane pump.

Therefore, in one embodiment of the invention, the first and second

membrane pumps can each comprise a membrane with a static perimeter, and they can be arranged with the static perimeter of their respective membranes in different planes. This can include having the pumps mounted at any angle, for example 45 or 135 degrees. In one version of the invention the first and second membrane pumps can be arranged with the static perimeter of their respective membranes in parallel planes. This could be with both pumps mounted at 90 degrees to horizontal, or with one horizontal and the other inverted. It will be appreciated that any angular relationship between the membrane pumps is possible.

The invention can be performed in various ways, but one embodiment will now be described by way of example, and with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a dispensing pump according to the present invention;

Figure 2 is a side view of the dispensing pump as shown in Figure 1 ; and

Figure 3 is a cross-sectional front view of the dispensing pump as shown in Figure 1 .

As shown in Figure 1 , a dispensing pump 1 comprises a motor (not visible), a driveshaft 2 rotatable by the motor in both a first direction, as indicated by arrow A, and a second direction opposite to said first direction, as indicated by arrow B, a first membrane pump 3 comprising a first operating plunger 4 mounted to the driveshaft 2 by a first coupling 5, and a second membrane pump 6 comprising a second operating plunger 7 mounted to the driveshaft 2 by a second coupling 8. As shown in Figure 3, the first coupling 5 comprises a cam body 9 which converts rotational movement of the driveshaft 2 into reciprocal movement of the first operating plunger 4. Further, the first coupling 5 comprises a clutch bearing 10 which is only engaged by rotation of the driveshaft 2 in the first direction A. The second coupling 8 is identical, save for the orientation of the clutch bearing 1 1 , which is only engaged by rotation of the driveshaft 2 in the second direction B.

Referring to Figure 3, the first membrane pump 3 comprises a membrane 12 with a static perimeter 13. The membrane 12 is resilient, and is mounted for movement over a pump chamber 14. The static perimeter 13 is held in place by being mounted between upper 15 and lower 16 body parts, which connect together to form the body 17 of the first membrane pump 3. The membrane 12 is moved up and down in priming and dispensing strokes by reciprocal movement of the first operating plunger 4, the outer end of which 18 comprises a head 19 which is mounted to a socket 20 formed in the centre 21 of the membrane 12. In Figure 3 the membrane 12 is shown at the bottom of the dispensing stroke. Opposite the membrane 12 is an inlet 22 and an outlet 23. A fluid inlet line (not shown) is fitted to the inlet 22, and provides a supply of chemical fluid to be dispensed, and a fluid outlet line (not shown) is fitted to the outlet 23 to dispense the chemical fluid to the associated washing machine. The inlet 22 and outlet 23 are provided with non-return valves (not shown) in the known way, so during the priming stroke the inlet 22 is open and the outlet 23 is shut, and during the dispensing stroke the inlet 22 is shut and the outlet 23 is open.

The first coupling 5 is mounted to the inner end 24 of the first operating plunger 4, and comprises an annular housing 25, a roller bearing 26 disposed radially inside the annular housing 25, the cam body 9, which is disposed radially inside the roller bearing 26, and the clutch bearing 10 which is disposed radially inside the cam body 9. The clutch bearing 10 comprises an aperture 27, in which the driveshaft 2 is fixed. The cam stroke is 1 .5mm in this case. Therefore, when the driveshaft 2 is rotated in the first direction A, the clutch bearing 10 is engaged and the cam body 9 is rotated inside the roller bearing 26. The roller bearing 26 and the annular housing 25 are therefore moved through an orbital path around an axis 28 of the driveshaft 2. This movement is transmitted via the first operating plunger 4 into reciprocal movement of the centre 21 of the membrane 12.

The second membrane pump 6 comprises all the same components as the first membrane pump 3 shown in Figure 3, save for the orientation of the clutch bearing 1 1 , which is only engaged by rotation of the driveshaft 2 in the second direction B. Referring to Figure 2, the bodies 17 and 29 of the first and second membrane pumps 3 and 6 are arranged horizontally next to one another, such that the static perimeters of their respective membranes (not visible in Figure 2) are in the same plane C-C. As such, gravity affects the first and second membrane pumps 3 and 6 in the same way, so their respective pumping performance is the same.

The dispensing pump 1 comprises a motor housing 30 from which the driveshaft 2 projects. A rear 31 of the first membrane pump 3 is releasably attached to a front 32 of the motor housing 30 by suitable means which are not shown, and with the first coupling 5 releasably mounted to the driveshaft 2. Further, a rear 33 of the second membrane pump 6 is releasably attached to a front 34 of the first membrane pump 3 by suitable means which are not shown, with the second coupling 8 releasably mounted to the drive shaft 2. The means which allows these parts to releasably connect together can be any known releasable mechanism. With regard to the mounting of the couplings 5 and 8 to the driveshaft 2, this is achieved by sliding the couplings 5 and 8 over the driveshaft 2 until the pump 3 or 6 is releasably mounted in its position.

The motor housing 30 houses the motor (not visible) which drives the driveshaft in the first and second directions A and B. It also comprises a

programmable electronic control system (not visible), which can be arranged to operate the first and second membrane pumps 3 and 6 in any manner required, and in particular to dispense particular quantities of chemical, at particular rates, and at particular times. In addition, the motor housing also contains a gear box which transmits movement from the motor to the driveshaft 2. Such arrangements are known, and are therefore not further described here.

The first and second membrane pumps 3 and 6 each comprise a cover 35, which is releasably mounted to their body 17 and 29 respectively, and which encloses the first and second operating plungers 4 and 7 respectively. These covers 35 are identical in each case, and are shown in cross-section in Figure 2 only. They are mounted to the bodies 17 and 29 with suitable means which are not shown. These means can be any known releasable mechanism.

The covers 35 each comprise a first support bearing 36 provided in a first side 37 thereof, which is releasably mounted to the driveshaft 2, and a second support bearing 38 provided in a second side 39 thereof, which is also releasably mounted to the driveshaft 2. The support bearings 36 and 38 are releasably mounted to the driveshaft 2 by sliding the covers 35 over the driveshaft 2 until the pump 3 or 6 is releasably mounted in its position. The support bearings 36 and 38 perform an important role in supporting and stabilising the driveshaft 2, which as is clear from the Figures is relatively long in order to pass through the coupling 8 of the second membrane pump 6, due to the manner in which the first and second membrane pumps 3 and 6 are arranged alongside one another.

The invention defined in the present application is embodied in the

arrangement so far described. In particular the invention comprises a first membrane pump 3 and a second membrane pump 6 mounted to the same driveshaft 2.

However, as is clear from Figure 1 , the dispensing pump 1 in the illustrated embodiment comprises a further motor (not visible) and a further driveshaft 40. The dispensing pump 1 therefore comprises two arrangements which fall within the scope of claim 1 below, which multiple configuration falls within the scope of claim 9 below.

The drive shaft 40 is the same as driveshaft 2 described above, and it is rotatable in both a first direction A and a second direction opposite to the first direction. In Figure 1 only one further membrane pump 41 is shown, however it will be appreciated that another can be mounted on the same driveshaft 40 in the manner of second membrane pump 6 mounted on driveshaft 2. The further membrane pump 41 is identical to membrane pump 3 described above, and the clutch bearing 42 is orientated so the membrane pump 41 operates when the driveshaft 40 is rotated in the first direction A. The arrangement shown on the second driveshaft 40 illustrates the flexibility inherent in dispensing pump 1 , which can be used to operate 1 , 2, 3 or 4 pumps at the same time, in any of the possible formations.

Therefore, in use the dispensing pump 1 is mounted in a convenient location adjacent to one or more washing machines. The user then mounts the required number of membrane pumps to the dispensing pump 1 , and in order to achieve an arrangement according to the present invention this would include mounting two membrane pumps with clutch bearing of the opposite orientation on at least one of the driveshafts 2 or 40, as is shown in the Figures with first and second membrane pumps 3 and 6 mounted on driveshaft 2. For the purposes of this illustrative example the user mounts the three membrane pumps 3, 6 and 41 in the manner shown in Figure 1 .

To mount a membrane pump on a driveshaft the user slides it over the end of the driveshaft, so it passes through the support bearings 36 and 38 of the cover 35, as well as through the aperture 27 of the clutch bearing in question. The membrane pump nearest the motor housing 30, which in this example is first membrane pump 3, is moved over the driveshaft 2 until the means to connect it to the motor housing (not shown) are engaged. The next membrane pump, which in this example is second membrane pump 6, is then mounted in the same way and moved down the driveshaft 2 until the means to connect it to the first membrane pump 3 (not shown) are engaged. The arrangement shown in Figure 2 is then achieved.

To complete the arrangement shown in Figure 1 , the membrane pump 41 is then mounted to driveshaft 40 in the same way as first membrane pump 3 is mounted to driveshaft 2.

The user then connects supply lines (not shown) to the inlets 22 of the membrane pumps 3, 6 and 41 , which are fed from the required supplies of washing chemicals. They then connect delivery lines (not shown) to the outlets 23 of the membrane pumps 3, 6, and 41 , which are fed to inlets of the associated washing machines. It will be appreciated that with the membrane pumps 3 and 6 mounted in the manner shown, the inlets 22 and outlets 23 are all conveniently aligned with one another in the horizontal plane, and are all easily accessible on the undersides of the pumps 3 and 6. This would not be the case if the membrane pumps 3 and 6 were mounted at different angles to one another.

The user can then program the dispensing pump 1 to operate as required, for example to supply a given quantity of detergent to a washing machine at a given flow rate at a given moment in the washing cycle, and to then supply a given quantity of a rinse aid to the washing machine, again at a given flow rate at a given moment. The user would specify which of the pumps 3, 6, and 41 were used each time.

The dispensing pump 1 is also electronically connected to the associated washing machine or machines, so it can receive signals which prompt it to operate as programmed.

In use the dispensing pump 1 operates to rotate the driveshaft 2 in the first direction A in order to operate membrane pump 3. When the driveshaft 2 is rotated on its axis 28 this engages the clutch bearing 10, which then rotates the cam body 9 in unison with the driveshaft 2. The cam body 9 rotates the roller bearing 26 and the annular body 25, moving them through an orbital path around the axis 28 of the driveshaft 2. This movement is transmitted via the first operating plunger 4 into reciprocal movement of the centre 21 of the membrane 12. This reciprocal movement flexes the membrane 12 up and down in priming and dispensing strokes. During the priming stroke the inlet 22 is opened by its non-return valve (not shown) and the outlet 23 is shut by its non-return valve (not shown), such that the chemical is drawn into the pump chamber 14. During the dispensing stroke the inlet 22 is shut by its non-return valve and the outlet 23 is opened by its non-return valve, such that the chemical in the pump chamber 14 is driven out of the outlet 23.

At a later time the dispensing pump 2 then operates to drive the driveshaft 2 in the second direction B to operate membrane pump 6. This then operates in the same manner as described above to pump a different chemical to the associated washing machine.

When the driveshaft 2 is rotated, either in direction A or direction B, it is supported along its length by four support bearings 36 and 38, which are provided in both of the covers 35. This ensures that the movement of the driveshaft 2 remains consistent and true along its length. Any deviation would lead to under or over performance, in particular of the second membrane pump 6, which is connected to the driveshaft 2 further along its length from the motor housing 30 than the first membrane pump 3, so any deviation would be more likely, and would have a greater effect.

As the first and second membrane pumps 3 and 6 are arranged horizontally next to one another, such that the static perimeters of their respective membranes are in the same plane C-C, gravity affects the first and second membrane pumps 3 and 6 in the same way, so their respective pumping performance is the same. This is important to ensure that the dispensing pump 1 can be readily programmed to deliver the required amounts each time. If there were any discrepancy between the pumping performances of the first and second membrane pumps 3 and 6, this would have to be factored into the way the motor was operated in terms of its rotation speed and duration of operation. This would add unnecessary complication and the risk of inadequate performance.

Therefore, the dispensing pump 1 uses just one motor to operate two membrane pumps 3 and 6 in the same way.

The dispensing pump 1 can also then operate the driveshaft 40 in the first direction A to operate membrane pump 41 . This then operates in the same manner as described above to pump a chemical to the associated washing machine. This action can be performed simultaneously with the rotation of the driveshaft 2 if necessary. It will be appreciated that a further membrane pump could be mounted to the driveshaft 40, so the arrangement on driveshaft 2 were duplicated.

In the event that a user wants to re-arrange the membrane pumps to a different configuration, or if one or more of the membrane pumps 3, 6 or 41 requires replacement, then they can remove them from the dispensing pump 1 in a reverse procedure to how they were mounted. The lines (not shown) are disconnected from the inlet 22 and the outlet 23, the means to connect the membrane pump (not shown) to the motor housing 30, or to another membrane pump, are disengaged, and the membrane pumps is then slid off the driveshaft in question.

The invention can be altered without departing from the scope of claim 1 . For example, in alternative embodiments (not shown) two membrane pumps are arranged on a driveshaft with the static perimeter of their respective membranes in different planes. This can include having the pumps mounted at any angle, for example 45 or 135 degrees. In some of these alternative embodiments the first and second membrane pumps are arranged with the static perimeter of their respective membranes in parallel planes. This includes having them both mounted at 90 degrees to horizontal, and with one horizontal and the other inverted. In some of the embodiments in which the membrane pumps are arranged at an angle greater than 90 degrees to one another, they are axially staggered on the driveshaft to reduce the axial length of the dispensing pump and bring the operating plungers closer together. In some of these embodiments gravity has a different effect on the two membrane pumps, but in order to compensate for this they are provided with a greater capacity or are operated differently, so the desired pumping performance is still achieved.

Therefore, the present invention provides a dispensing pump with one motor, which can operate two separate membrane pumps by rotating in opposite directions. Further, the membrane pumps are preferably mounted with their membranes in the same plane, so the performance is equalised. In addition, support bearings are provided to ensure that the relatively long driveshaft rotates in a uniform manner along its length. The invention provides all the advantages of the known dispensing pumps which operate two peristaltic pumps on one driveshaft, but avoids the drawbacks associated with peristaltic pumps in general.

Claims

1 . A dispensing pump comprising a motor, a driveshaft rotatable by said motor in both a first direction and a second direction opposite to said first direction, a first membrane pump comprising a first operating plunger mounted to said driveshaft by a first coupling, and a second membrane pump comprising a second operating plunger mounted to said driveshaft by a second coupling, in which said first coupling and said second coupling each comprise a cam body which converts rotational movement of said driveshaft into reciprocal movement of said first operating plunger and second operating plunger respectively, in which said first coupling and said second coupling each comprise a clutch bearing which is only engaged by rotation of said driveshaft in said first direction and said second direction respectively.

2. A dispensing pump as claimed in claim 1 in which said first membrane pump and said second membrane pump each comprise a membrane with a static perimeter, and in which said first membrane pump and said second membrane pump are arranged with the static perimeter of their respective membranes in the same plane.

3. A dispensing pump as claimed in claim 2 in which said first membrane pump and said second membrane pump each comprise a body which defines a pump chamber, and in which said first membrane pump and said second membrane pump are arranged with their respective bodies alongside one another.

4. A dispensing pump as claimed in claim 3 in which said dispensing pump further comprises a motor housing from which said driveshaft projects, and in which a rear of said first membrane pump is releasably attached to a front of said motor housing, with said first coupling releasably mounted to said driveshaft.

5. A dispensing pump as claimed in claim 4 in which a rear of said second membrane pump is releasably attached to a front of said first membrane pump, with said second coupling releasably mounted to said drive shaft.

6. A dispensing pump as claimed in claim 5 in which said first membrane pump and said second membrane pump each comprise a cover which is releasably mounted to the body of the first membrane pump and second membrane pump respectively, and which encloses said first operating plunger and said second operating plunger respectively.

7. A dispensing pump as claimed in claim 6 in which the covers of the first membrane pump and the second membrane pump each comprise a first support bearing provided in a first side thereof, which is releasably mounted to said driveshaft.

8. A dispensing pump as claimed in claim 7 in which the covers of the first membrane pump and the second membrane pump each comprise a second support bearing provided in a second side thereof, which is releasably mounted to said driveshaft.

9. A dispensing pump as claimed in claim 1 , in which said dispensing pump comprises one or more further motors, each of which comprises a further driveshaft rotatable thereby in both a first direction and a second direction opposite to said first direction, and in which said dispensing pump comprises one or more further membrane pumps each comprising an operating plunger mounted to a further driveshaft by a coupling comprising a cam body which converts rotational movement of that further driveshaft into reciprocal movement of that operating plunger, that coupling comprising a clutch bearing which is only engaged by rotation of that further driveshaft in said first direction or said second direction.

10 A dispensing pump as claimed in claim 1 in which said first membrane pump and said second membrane pump each comprise a membrane with a static perimeter, and in which said first membrane pump and said second membrane pump are arranged with the static perimeter of their respective membranes in different planes.

1 1 . A dispensing pump as claimed in claim 10 in which said first membrane pump and said second membrane pump are arranged with the static perimeter of their respective membranes in parallel planes.

12. A dispensing pump substantially as described herein and as shown in the accompanying drawings.