Pump

Abstract

 A pump has an elongate pump chamber (22) with a flexible tube disposed along the chamber and which is compressible to reduce the volume of the tube and cause fluid in the tube to pass along the tube, the flexible tube being disposed within the chamber in a state in which it occupies the full volume of the chamber. A pair of valves (30) are provided, one at each end of the chamber, and the valves are individually actuatable to close off the flexible tube during operation of the pump. A compression element (23) is movable over a given distance to reduce the volume of the chamber and hence the volume of the flexible tube by an amount substantially equal to the swept volume of the compression element.

Description

BACKGROUND

[0001] The present invention relates to pumps and, more particularly, to pumps in which one or more compression elements move to compress a flexible tube over a given length to cause fluid in the tube to be pumped from it by the reduction in volume which occurs with the compression of the tube. Such pumps are generally known as peristaltic pumps owing to the similarity over operation with the peristalsis which occurs in body lumens to move fluid through them.

[0002] A number of different types of pump are known in the laboratory instrument and health care fields, for example positive displacement pumps such as diaphragm pumps, piston-operated pumps and syringe pumps. Such pumps are used to supply or deliver accurate amounts of fluid. However, they are disadvantageous in uses which require sterility to be maintained because of the difficulty of achieving thorough washing. Similarly, they are disadvantageous where there are frequent changes in the fluid being delivered, in particular where no contamination between one fluid sample and another is required to be assured, since they generally require autoclaving, flushing or otherwise sterilizing, or replacement altogether in such circumstances. Peristaltic pumps, in this context, pumps which have one or more compression elements movable to compress a flexible tube over a given length to cause fluid in the tube to be pumped from it by the reduction in volume which occurs with the compression of the tube, are frequently used instead as the flexible tubes can easily be replaced when different fluids are to be pumped, without significant cost overhead. In other cases, since the tubes are easy to wash/clean, sterility can be maintained easily without replacement of the tubes. Some peristaltic pumps rely on rotary motion of one or more rollers to compress the tube to a flattened state around an arcuate path and others are linear' in that one or more compression elements close the tube in turn along a path, but without a rolling action of the compression element(s).

[0003] Such peristaltic pumps are well known in the laboratory instrument and health care fields. Prior art of background relevance can be found in GB-A-2150644, US-A-4671792, US-A-5868712, US-A-4039269 & US-A-6213739.

[0004] A particular difficulty which it is desirable to overcome is that of consistency of volumetric change and hence the volume of fluid delivered at each stroke of the pump. This is a particular issue in laboratory apparatus where the volumes to be delivered may be very small (in the region of small numbers of microlitres). Relatively minor variations in the wall thickness (which can affect the internal diameter) of the flexible tubes used in such pumps can result in significant variations in fluid volumes delivered. In particular with multi-channel pumps where it is desired to deliver equal volumes from the different channels, for example in chemical or biological assay work or drug development work, variations are problematic.

[0005] Existing linear peristaltic pumps, for example those referred to in the prior art documents mentioned above, whilst providing generally desirable pumping characteristics, do not solve the issue of variability referred to above.

STATEMENT OF INVENTION

[0006] A pump comprising:

an elongate pump chamber;

a flexible tube disposed along the chamber and which is compressible to reduce the volume of the tube and cause fluid in the tube to pass along the tube, wherein the flexible tube is disposed within the chamber in a state in which it occupies the full volume of the chamber;

a pair of valves, one at each end of the chamber, and individually actuatable to close off the flexible tube during operation of the pump; and

a compression element movable over a given distance to reduce the volume of the chamber and hence the volume of the flexible tube by an amount substantially equal to the swept volume of the compression element.

[0007] The present invention solves the problem of variability of delivery volumes caused by changes in tube dimensions, by a construction in which the delivery volume is arranged to be largely unrelated to the tube dimensions. By arranging for the pump chamber volume change to be defined by the movement of the compression element, i.e. its swept volume, minor variations in tube dimensions, e.g. tube wall thickness or internal bore diameter, do not affect the delivery volume either from one chamber to another in a multi-chamber pump or when the flexible tube is changed either to avoid contamination of samples or because of wear.

[0008] In one type of pump, the movable element engages the flexible tube.

[0009] The pump may include tube clamping elements at each end of the chamber to prevent or minimise longitudinal movement of the flexible tube.

[0010] The pump may include fixed tubular components at each end of the chamber to prevent or minimise longitudinal movement of the flexible tube.

[0011] Alternatively, the pump may include including fixed tubular components at each end of the chamber to prevent or minimise longitudinal movement of the flexible tube.

[0012] In other examples, the pump may include the flexible tube is contoured at each end of the chamber and the pump includes housing components matching the tube profile to prevent or minimise longitudinal movement of the flexible tube.

[0013] To smooth the flow of fluid through the pump the flexible tube may include a further chamber and a corresponding further movable element arranged to operate out of phase 180° with the first movable element and to move only half the swept distance of the first movable element. The second chamber and movable element may be disposed on the outlet and/or the inlet side of the first chamber.

[0014] Preferably, the valves are pinch valves. The internal tube diameter of the flexible tube at the pinch valves may be smaller than that within the chamber and/or the external tube diameter of the flexible tube at the pinch valves may be smaller than that within the chamber.

[0015] In a further design, an elastomeric element may be disposed between the movable element and the flexible tube to transfer the volume displacement of the movable element to the flexible tube.

[0016] In a yet further design, a fluid filled chamber, having an elastomeric membrane disposed against the aside of the flexible tube, is disposed to transfer the volume displacement of the movable element to the flexible tube.

[0017] Preferably the chamber is cylindrical and either of circular or rectangular cross-section to facilitate a tight fit with the flexible tube. The flexible tube may be pre-compressed into the pump chamber (i.e. an 'interference' fit) or else is arranged to be of external dimensions exactly the same as the internal dimensions of the chamber.

[0018] It may be noted that there is no need for the flexible tube to be completely closed (indeed this is undesirable) by the movement of the compression element, the pinch elements being used to prevent back-flow in operation.

[0019] The chamber may include a movable wall portion acted upon by the compression element to reduce the chamber volume. Preferably, the chamber has a pair of semi-circular cross-sectioned chamber halves, into which the flexible tube is fitted under pre-compression, and which are movable towards one another in operation to change the chamber volume. Preferably one of the chamber halves is fixed and the other movable relative to it.

[0020] The valves may be pinch elements arranged to close off the tube by squeezing it or may be separate valves to which the flexible tube is fitted at each end. The valves do not have to be immediately adjacent the chamber but may be spaced from the ends of the chamber to suit requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Examples of pumps according to the present invention will now be described in accordance with the accompanying drawings in which:

Figures 1A to 1C are end, longitudinal section and plan section views through a first pump;

Figures 2A to 2C are end, longitudinal section and plan section views through a second pump;

Figures 3 is a cross-section through the pumps of figures 1A to 1C and 2A to 2C;

Figures 4 & 5 are partial cross-sections through prior art pumps at different stages of operation;

Figure 6 is a partial cross-section through the pump of figures 1A to 1C or 2A to 2C at different stages of operation;

Figure 7 to 10 illustrate, in cross-section, different methods of causing the required volumetric change according to the invention;

Figures 11 to 13 illustrate alternative cross-sections through pumps according to the invention;

Figures 14 to 17 illustrate schematic partial longitudinal sections through a number of pump designs; and

Figures 18 to 20 illustrate schematic partial cross-sections of further pump designs.

DETAILED DESCRIPTION

[0022] Figures 1A to 1C illustrate a first pump having a housing 1 formed with a lower housing 10 and a closure or top plate 11. The pump is an 8 channel linear pump and Figure 1A shows one end of the pump with eight flexible tubes 20 shown positioned in corresponding channels 21. For simplicity and clarity Figures 1B and 1C do not show the tubes 20. Each of the channels 21 is generally cylindrical and, at a central part has a chamber 22 which is defined on one side by a linearly movable element 23 which has a substantially semi-cylindrical surface forming one side of the chamber 22 (see Figures 3 and 6). The tubes are formed of a flexible rubber-like material, for example silicone, but may be of Marprene®, Viton®, Tygon® or similar proprietary materials.

[0023] At each end of the bank of channels 21, as best seen in Figures 1 B and 1C, pinch valves 30 are provided, formed by elongate protrusions 31 on the underside of the top closure plate 11 and by corresponding and opposed protrusions 32, disposed on elongate valve blocks 33. Within the lower housing 10 a drive mechanism 12 is provided for causing movement of the valve blocks 33 and movable element 23 in order to control the pumping action, the relative timings of the opening and closing of the pinch valves 30 and the compression of the tubes 20 within the chambers 22 being in accordance with Table 1 below.

Table 1

	Inlet Valve (30)	Movable Element (23)	Outlet Valve (30)
1	Open	Relaxing	Closed
2	Open	Stationary	Closed
3	Closed	Stationary	Closed
4	Closed	Stationary	Open
5	Closed	Compressing	Open
6	Closed	Stationary	Open
7	Closed	Stationary	Closed
8	Open	Stationary	Closed

[0024] The left hand part of Figure 6 shows the corresponding shape of the flexible tube 20 and the chamber 22 in an exploded, partial cross-sectional view, the centre view showing the arrangement after assembly and the right hand view showing the relative disposition of the component parts on compression of the tube 20. Each of the views shows only one of the channels through the pump 1. As can be seen from the centre view, the tube 20 is a full or even interference fit within the chamber 22 but the opposing faces of the movable element 23 and the top plate 11 are slightly spaced apart from one another so that when compression is required in order to cause pumping of fluid through the tube 20, the volume of the chamber 22 is reduced and, correspondingly, the volume of the bore 24 within the flexible tube 20 is reduced. Preferably, even in the fully compressed position as shown in the right hand view of Figure 6, there is a slight gap between the opposing faces of the closure plate 11 and movable element 23. This can be used to avoid interference from foreign particles such as dust or grit preventing the correct movement of the movable element 23. It will be appreciated that the movement of the movable element 23 to compress the tube 20 alters the volume of the chamber 21 in so such a way that there is a corresponding reduction of the volume of the bore 24 within the chamber 22 so that minor variations or inconsistencies in the thickness of the wall 25 of the tube 20 do not affect the volumetric change which occurs and therefore the consistency of volumetric pumping between adjacent chambers in a multi-chamber pump or when the tubes 20 are replaced.

[0025] Typically the flexible tube has an outer diameter of 4mm and an internal diameter of 2mm, with the chamber 22 having a length of 20mm. The movable element 23 may move over a given distance of 0.15mm, providing a swept volume of 12µl, so that the pumped volume per cycle is 12µl. Accuracy and repeatability of better than 1% may be provided.

[0026] The difference over the prior art can be seen between the volumetric change occurring in a pump according to the present invention by comparing Figure 6 with Figures 4 and 5 which show conventional arrangements for squeezing the flexible tube in a linear peristaltic pump. In both of these examples it can be seen that the closure element C squeezes the tube T in such a way that the shape of the tube T is considerably deformed and, because the shape of the tube T is not constrained to remain the same, the movement of the compression element C results in "lost movement" either of the tube or within the chamber in which the tube fits, leading to potential inconsistencies in the volume of fluid pumped, either as a result of differential collapsing of the tube wall between different tubes or because of the changes in the tube dimensions which alter the volume of fluid squeezed out of the tube as it is compressed.

[0027] Preferably, when the closure plate 11 is fixed onto the lower housing 10, the flexible tubes 20 are slightly compressed from their natural, uncompressed condition, within the channels 21, including within the chambers 22, which not only ensures that the tubes 20 occupy the full volume of channels 21 and in particular the channels 22, but also provides for better recovery on decompression which in turn leads to increased suction and hence better pumping as the movable element 23 returns to its retracted position.

[0028] Figures 2A to 2C illustrate a similar pump, but this pump includes a further movable element 43 substantially identical to the movable element 23, but arranged, by virtue of the drive mechanism 12, to operate out of phase 180° with the movable element 23 and to move only half the swept distance of the movable element 23 in order to smooth the flow of fluid through the tubes 20. This is particularly advantageous when pumping fluids which include delicate cells which may be otherwise damaged by pumping action. The operating sequence is shown in Table 2 below.

Table 2

	Inlet Valve (30)	Movable Element (23)	Outlet Valve (30)	Smoothing Element (43)
1	Open	Relaxing	Closed	Compressing
2	Open	Stationary	Closed	Stationary
3	Closed	Stationary	Closed	Stationary
4	Closed	Stationary	Open	Stationary
5	Closed	Compressing	Open	Relaxing
6	Closed	Stationary	Open	Stationary
7	Closed	Stationary	Closed	Stationary
8	Open	Stationary	Closed	Stationary

[0029] The particular construction of the drive mechanism 12 in the case of either of the examples in Figures 1 and 2 is not of particular significance, but preferably comprises appropriate rotatable cam surfaces arranged to control the movement of the movable elements 23, 43 and the valves 30.

[0030] Figure 7 is a partial cross-section through a pump similar to that of Figures 1 and 2 in which the chamber 22 is oval in cross-section.

[0031] In the pump shown in Figure 8, the chamber is clamped on one side in cantilevered fashion and compression of the chamber occurs by movement on substantially one side in pivotal type of motion.

[0032] In the pump shown in Figure 9, multiple movable elements 23 are arranged in the form of segments around the axis of the tube 20.

[0033] Figure 10 shows an alternative construction in which the tube 20 and chamber 22 are arranged to be compressed in a longitudinal direction by relative longitudinal movement between a movable element 23 and an opposing fixed element 24.

[0034] Figures 11, 12 and 13 show further possible alternative constructions for the chambers 22, tubes 20 and movable elements 23 to achieve consistent volumetric change within the chambers 22.

[0035] In Figure 11 the movable element 23 has a protrusion (or piston) 231 which forms the compression element and which has an arcuate cylindrical end face 232, the protrusion 231 sliding within an extension (or piston chamber) of the chamber 22 which provides an arcuate surface 233 opposite the arcuate surface 232. The chamber 22 is circular in cross-section and the arcuate surfaces 232, 233 are also part-circular. The diameter of the chamber 22 and hence the outer diameter of the pre-compressed flexible tube after installation is 1.8mm, the internal diameter of the tube (or diameter of the bore) is about 0.7mm and the projection is spaced by a clearance of about 0.05mm from the piston chamber surface. T

[0036] In Figure 12 the chamber 22 is square in cross-section and the movable element 23 has a protrusion 234 with a flat end surface engaging one side of the square tube 20.

[0037] Figure 13 again shows a square tube 20 and chamber 22, but in this case the chamber is formed between two substantially identical halves 235, 236 and is thus closer to the design shown in Figures 1, 2 and 6.

[0038] Figure 14 is a partial longitudinal section through a pump showing an extended tube squeezing section or chamber 22 where the amount of elongate tube extrusion on compression of the tube 20 is small compared with the swept volume of the movable element 23 and hence the pumped volume.

[0039] Figure 15 is a partial longitudinal section through a pump showing tube clamping sections 25 at each end of the chamber 22 and the movable element 23 to allow any longitudinal tube extrusion beyond the squeezing element to be converted into radial bore reduction.

[0040] Figure 16 is a partial longitudinal section through a pump showing a tubing set with connectors 203 between an inlet tube 201 , the tube 20 within the chamber 22 and an outlet tube 202. The connectors 203 fit into slots 204 in the pump housing 10 which prevents them from moving. This in turn ensures that the volume displaced by the movable element 23 is all converted into a reduction of the tube bore corresponding to the swept volume of the movable element 23. The inlet tube 201, squeezed tube 20 and the outlet tube 202 do not need to be the same diameter.

[0041] Figure 17 is a partial longitudinal section through a pump showing a tube 20 with different sections 201, 202, 205, 206, 207 having different cross -sections. A thinner wall ed section 205, 207 at each end of the chamber 22 between the tube section 206 and inlet and outlet sections 201, 202, minimises tube extrusion. The chamber housing 10 is profiled to fit the tube sections.

[0042] Figure 18 is a partial cross-section through a pump showing an elastomeric compressing element 231 with a flat upper surface 232 and a lower curved surface 233 to suit the diameter of the tube 20. The elastomeric element 231 is attached to the bottom of a movable element 23 in the form of a movable piston to transfer the volume displacement of the movable element to the flexible tube. The flexible element 231 is confined on all surfaces except where it contacts the tube.

[0043] Figure 19 is a partial cross-section through a pump showing a similar elastomeric element 234, except that the piston 23 has a reduced cross-section.

[0044] Figure 20 is a partial cross-section through a pump showing a fluid-filled side chamber 235 on the upper side of the chamber 22, with a thin-walled membrane 236 closing the lower side of the side chamber 235 and separating the fluid within the chamber 235 from the tube 20. Seals 237 are used around a piston 238 forming the movable element to contain the fluid. In each of the designs shown in Figures 18 to 20, the swept volume of the movable element 23/238 causes a corresponding reduction in the volume of the tube 20 via the elastomeric element 231,234 or fluid-filled side chamber 235.

Claims

1. A pump comprising:

an elongate pump chamber;

a flexible tube disposed along the chamber and which is compressible to reduce the volume of the tube and cause fluid in the tube to pass along the tube, wherein the flexible tube is disposed within the chamber in a state in which it occupies the full volume of the chamber;

a pair of valves, one at each end of the chamber, and individually actuatable to close off the flexible tube during operation of the pump; and

a compression element movable over a given distance to reduce the volume of the chamber and hence the volume of the flexible tube by an amount substantially equal to the swept volume of the compression element.

2. A pump according to claim 1, wherein the movable element engages the flexible tube.

3. A pump according to claim 1, including tube clamping elements at each end of the chamber to prevent or minimise longitudinal movement of the flexible tube.

4. A pump according to claim 1, including fixed tubular components at each end of the chamber to prevent or minimise longitudinal movement of the flexible tube.

5. A pump according to claim 1, wherein the flexible tube is contoured at each end of the chamber and the pump includes housing components matching the tube profile to prevent or minimise longitudinal movement of the flexible tube.

6. A pump according to claim 1, which includes a further chamber and a corresponding further movable element arranged to operate out of phase 180° with the first movable element and to move only half the swept distance of the first movable element in order to smooth the flow of fluid through the flexible tube.

7. A pump according to claim 6, wherein the second chamber and movable element are disposed on the outlet side of the first chamber.

8. A pump according to claim 6, wherein the second chamber and movable element are disposed on the inlet side of the first chamber.

9. A pump according to claim 1, wherein the valves are pinch valves.

10. A pump according to claim 9, wherein the internal tube diameter of the flexible tube at the pinch valves is smaller than that within the chamber.

11. A pump according to claim 9, wherein the external tube diameter of the flexible tube at the pinch valves is smaller than that within the chamber.

12. A pump according to claim 1, wherein an elastomeric element is disposed between the movable element and the flexible tube to transfer the volume displacement of the movable element to the flexible tube.

13. A pump according to claim 1, wherein a fluid filled chamber, having an elastomeric membrane disposed against the aside of the flexible tube, is disposed to transfer the volume displacement of the movable element to the flexible tube.

14. A pump according to claim 1, wherein the chamber and the flexible tube each have a substantially circular cross-section and hence a substantially circular surface, and the compression element comprises a piston having an arcuate surface forming part of the substantially circular surface of the chamber and movable relative to the other part or parts of the substantially circular surface of the chamber to change the volume of the flexible tube.

15. A pump according to claim 14, wherein the piston is arranged to be movable within a piston chamber connecting with the chamber and having a cross-sectional dimension the same as the diameter of the chamber.

Drawing