GB2379719A

GB2379719A - Flexible tube pump

Info

Publication number: GB2379719A
Application number: GB0122550A
Authority: GB
Inventors: Stewart Patrick Douglas Shaw
Original assignee: Shaw Stewart P D
Current assignee: Shaw Stewart P D
Priority date: 2001-09-18
Filing date: 2001-09-18
Publication date: 2003-03-19
Also published as: GB0122550D0

Abstract

In a flexible tube pump, a flexible tube 1 passes through a chamber 2 which is filled with a incompressible material 6, the incompressible material is moved, thereby compressing the flexible tube 1 and pumping fluid. Inlet and outlet valves 4 and 5 at upstream and downstream ends of the flexible tube control the flow of the fluid through the tube. The means of moving the incompressible material may be by reducing the volume of the chamber, ie by using a piston 7 or diaphragm, or by introducing more incompressible material into the chamber. The means for moving the incompressible material may be controlled by a piezo-electric device. The tubing may have an oval cross section. The tubing may be bent or coiled as it passes through the chamber. The incompressible material may be a liquid, gel or elastic solid. The valves may be automatic non-return valves The valves may have a Peltier device and may operate by freezing the fluid to prevent flow.

Description

Description General features of the invention This invention relates to an apparatus for accurately pumping fluids, especially liquids. It is a pump that combines some of the best features of piston pumps etc, which are accurate, with some of the best features of peristaltic pumps etc. , which are easily flushed out and which do not trap bubbles.

The apparatus is a pump that comprises two valves situated upstream and downstream of a length of flexible tubing that passes through a sealed chamber, hereinafter referred to as the pumping chamber Said length of tubing gives rise to the pumping action and is hereinafter referred to as the active tube.

The pumping chamber has rigid walls. The spaces in the pumping chamber around the active tube are filled either with a liquid such as water, oil, polymer, liquid hydrocarbon, solvent, halogenated hydrocarbon, emulsion, colloid, silicone oil or mercury, or with an elastic material such as silicone rubber, natural rubber, synthetic rubber, organic polymer, agar gel or other gel. Many other liquids or elastic materials can be used to fill the pumping chamber. It is helpful if the liquid or elastic material completely fills the pumping chamber and surrounds the active tube and that there are no bubbles or pockets of air in the pumping chamber. Any air present within the pumping chamber will reduce the accuracy of the apparatus. Some advantages of using an elastic material rather than a liquid are that it is impossible for air bubbles to form in the pumping chamber, and that leaks are eliminated.

The apparatus operates with a cycle that comprises the following steps: 1. The valve upstream of the pumping chamber closes 2. The valve downstream of the pumping chamber opens 3. The tube in the pumping chamber is compressed, either by reducing the volume of the pumping chamber or by introducing more liquid or elastic material into the pumping chamber, thereby expelling fluid out of the apparatus 4. The downstream valve closes 5. The upstream valve opens 6 The tube in the pumping chamber is allowed to expand either by increasing the volume of the pumping chamber or by removing liquid or elastic material from the pumping chamber, thereby sucking fresh fluid from a reservoir or other source into the apparatus.

The operation of the valves is similar to many other pumps such as piston, finger or diaphragm pumps.

The direction of pumping can be reversed, in which case the roles of the two valves are swapped with each other.

Steps 1 and 2 can be carried out rapidly and simultaneously, likewise steps 4 and 5, giving a simpler, but possibly less accurate, four-step cycle. To maintain accuracy, the state of the valves would in this case have to change rapidly so that the valves would be open together only for an insignificant period The expansion of the tube in step 6 is caused by the elasticity of the tube, by the elasticity of the material that fills the pumping chamber if an elastic material is used rather than a liquid, and by (e. g. atmospheric) pressure acting on the inside of the tube Many different types of valves can be used. For example, pinch valves, rotating barrel valves and slide valves are all appropriate Needle valves and diaphragm valves can also be used but they are less appropriate because they include space that is not efficiently swept out so that it will be more difficult to change the fluid being pumped than with pinch, barrel and slide valves. Needle valves and diaphragm valves may also trap air.

An alternative type of valve could be used that prevents flow by freezing the fluid being pumped For example Peltier devices placed close to the flow path of the fluid could be used as valves.

The performance of the apparatus may be improved by using an active tube that is coiled, flattened, has an oval cross-section, or has a set on it. This may make it easier to compress the active tube than would be the case with a round tube, since the tube will preferentially become compressed in a particular direction. (The tube will tend to become compressed such that the flattening is increased.)

In a variation in the design of the apparatus automatic non-return valves are used. For example duckbill valves, reed valves or valves with balls can be used. In this case the pumping action automatically closes the valves In such a case, the cycle of operation of the apparatus would be slightly different as follows la. The tube in the pumping chamber is compressed causing the upstream non-return valve to close and the downstream valve to open.

Ib. The tube in the pumping chamber continues to be compressed until the desired volume of fluid has been pumped 2a. The tube in the pumping chamber is allowed to expand causing the upstream valve to open and the downstream valve to close.

2b The tube in the pumping chamber continues to expand until the apparatus is fully recharged with fresh fluid Some automatic non-return valves are less accurate than other types of valves, because a significant amount of fluid may pass through them in the reverse direction before they close. Such valves may not be suitable for low-volume applications or applications demanding a high level of accuracy. Other, more accurate non-return valves, or actively driven valves, are suitable for applications demanding a high level of accuracy.

Because the liquid or elastic material surrounding the active tube in the pumping chamber is substantially incompressible, the volume of fluid expelled from the apparatus can be precisely determined. The apparatus is particularly appropriate for dispensing small quantities of liquids in the range from a few picoliters to a milliliter The apparatus can also be used for larger volumes, however, where the advantages of accuracy and zero dead-volume may be useful. Applications include chemical or biochemical testing or analysis, chemical or biochemical synthesis, fermentation, combinatorial chemistry, genetic analysis, DNA analysis, DNA sequencing, DNA synthesis, protein or peptide analysis sequencing or synthesis, the crystallization of biological macromolecules, clinical testing, medical diagnostics, food processing, food analysis, environmental analysis, industrial dispensing for manufacture, lubrication, additive dosing, fuel delivery, glue delivery, etching, polymer synthesis,

polymer dosing, agriculture, and, generally, accurate dosing or dispensing. t A variety of means can be used to compress the active tube. For example, the pumping chamber can be equipped with a diaphragm that can be moved thereby reducing the volume of the pumping chamber A diaphragm, however, is generally made from a flexible, compliant and elastic material and it may therefore be a less accurate method of displacing fluid from the apparatus. Alternatively, one wall of the pumping chamber can be thinner than the other walls and made of springy material so that it can be flexed as described below. Thirdly, the pumping chamber can be equipped with a piston. A fourth alternative is to equip the pumping chamber with an inlet port and a means of introducing liquid etc so that the active tube can be accurately compressed. Fifthly, a gear pump or the equivalent can be used.

Sixthly, a piezo-electric device can be used.

To maintain accuracy, it is important that no air bubbles become lodged in the flow path of the apparatus, including the active tube and the tubes or conduits that it is connected to. This is particularly important for applications where low volumes are pumped. It is therefore helpful to design the apparatus so that the fluid path does not include any rapid changes in diameter or profile, because air bubbles tend to lodge in such sites. Preferably, conduits and tubes with the same inner diameter should be used throughout. If it becomes necessary to change the profile or diameter, gradual changes in profile should be used. For example, to connect the active tube to tubing with a different diameter, a taper can be included in the bore of the smaller diameter tubing so that the change in diameter as one moves along the flow path is gradual.

The volume pumped in each cycle can advantageously be chosen so that many small volumes can be dispensed or pumped in each cycle. For example, the apparatus can be used to dispense liquids into the wells of a microtitre or tissue culture plate. An apparatus with a cycle volume greater than that of many wells would then be selected, so that the apparatus would have to be recharged (steps 4,5, 6, 1 and 2 above) relatively infrequently, after many wells had been dispensed. In other words, step 3 can be divided into many small movements.

Advantageously, both valves of the apparatus can be opened simultaneously so that the apparatus can be cleaned and flushed with the fluid to be pumped in order to prime it. An additional source of pressure would then be needed to move fluid through the apparatus. For example, a reservoir of the fluid to be dispensed can be placed in a gas-tight box, which is pressurized. When both valves of the apparatus are opened, fluid will then pass through the apparatus, and out of e. g. a dispensing nozzle into waste, thus priming the apparatus Alternatively, a peristaltic, centrifugal or other pump can be placed in series with the apparatus, and used to prime the apparatus. A third alternative would be to use gravity to prime the apparatus An alternative embodiment of the device has only one valve, which is placed upstream of the pumping chamber As described above, this valve is closed before the compression of the active tube, and opened before expansion of the active tube. In such an embodiment, gravity or hydrostatic pressure can prevent significant backward flow of the fluid Secondly, a small diameter tube or a constriction downstream of the pumping chamber will reduce flow in the reverse direction. Thirdly, surface tension acting at a small diameter orifice or at a pinning edge can prevent flow in the reverse direction.

Fourthly, a pump upstream of the device can prevent backward flow of the fluid Advantages 1. The apparatus is very accurate and is less affected by pressure gradients, changes in viscosity, or changes in the resistance to flow etc. than are many other pumps.

2 Large air bubbles can be reduced or eliminated, which further contributes to accurate pumping.

3 The apparatus has no dead volume, i. e the whole volume of the apparatus is swept out efficiently during pumping. This means that the apparatus can be cleaned and that the fluid being pumped can be changed rapidly with the minimum wastage of fluid.

Description of the invention with reference to figures The invention will now be described with reference to the accompanying figures. These figures are included to illustrate the invention with examples, and should not be interpreted so as to limit the scope of the invention. Like numerals are used to indicate like features in all figures.

Figure 1 shows a schematic view of the apparatus. The active tube (1) passes through the pumping chamber (2). The active tube forms a seal (3) or is equipped with seals where is passes through the walls of the pumping chamber. The active tube is connected to two valves, one upstream of the pumping chamber (4) and one downstream (5) of it. (The direction of pumping of the apparatus can, however, be reversed). The pumping chamber is filled with an incompressible material (6), which is either a liquid or an elastic material. This incompressible material surrounds the active tube excluding all gas or air bubbles The pumping chamber is equipped with a means of displacing the incompressible material, shown here as a piston (7).

Figures 2a-2fshow the six steps of the cycle of the apparatus described above. At the beginning of the cycle, both valves (4) and (5) are closed, figure 2a The downstream valve (5) then opens, figure 2b.

The piston (7) now moves to compress the active tube (1), expelling fluid from the apparatus, figure 2c In figure 2d, the downstream valve (5) has closed so that both valves are again in their closed state.

The upstream valve (4) then opens, figure 2e, and the piston (7) is withdrawn, figure 2f, sucking fresh fluid into the apparatus. The cycle is now repeated Figure 3 shows a schematic view of a variation of the apparatus. Here the piston is replaced with a springy sheet (8) made from e. g. metal, glass or plastic. As before, the apparatus comprises an active tube (I) equipped with two valves (4) and (5), which passes through a pumping chamber (2) filled with incompressible material (6). The apparatus is equipped with a means (9) of applying a force to and bending the springy sheet. For this purpose, screw threads, cams, motors, solenoids, pistons etc can be used. Solid lines indicate the positions of components before compression of the active tube, dotted lines their positions after compression This variation where a springy sheet is used has the advantages (i) that a very well sealed chamber can more easily be constructed and maintained than with e. g. a piston, and (ii) that variations in friction have little effect on the performance of the apparatus. It has the disadvantage that the displacement of the center of the springy sheet is non-linear with respect to

the displacement of fluid, so that the apparatus needs to be calibrated By using a computer or microprocessor system with a look-up table, however, accurate pumping can easily be obtained. Such a look-up table would relate a set of displacements of the springy sheet to the corresponding set of volumes pumped. Instead of a look-up table, a mathematical function can be used. A similar result can also be obtained mechanically by using a cam.

Note that low energy consumption of the apparatus may not be of primary importance for volumetric applications Accuracy may be more important. Therefore a springy sheet (8) that is relatively stiff can be used, that requires significant force to bend it. The apparatus can then be designed so that the force required to bend the flexible sheet is much greater than the force required to compress the active tube and to expel fluid from the apparatus. This eliminates the problem of second order effects, where variations in the pressure in the lumen of the active tube might cause variations of the exact bending profile of the flexible sheet, which would in turn give variations in the amount of fluid pumped Figure 4a shows a feature that can improve the performance of the apparatus A profiled plate (28) that has a convex protruding surface (29) is placed above the springy sheet. The springy sheet (8) is compressed by the convex surface of the plate The convex surface is designed to mate with the springy sheet when the springy sheet is fully compressed. This will increase the area of contact with the springy sheet, reduce the potential movement of the springy sheet, and have the effect of increasing the accuracy of the apparatus and reducing changes in its performance over time. Figure 4b shows the apparatus when the springy sheet is fully compressed by the profiled plate.

Figure 5 shows a preferred embodiment of the invention. It comprises an active tube (1) passing through a pumping chamber (2), which is filled with incompressible material (6). The active tube is coiled to increase its length without greatly increasing the dimensions of the pumping chamber. The active tube is connected to two barrel valves, one upstream (4) and one downstream (5) of the pumping chamber. The active tube passes through holes in the side walls of the pumping chamber which have diameters that are slightly smaller than the diameter of the active tube, which compresses the active tube, thus providing a seal (3). The top of the pumping chamber is formed by a springy sheet (8), which is clamped in position by a lid (10). This lid possesses a threaded hole (11) in which a screw (12) can rotate. The screw is turned by an electric motor (13) via a suitable dog or coupling (14). An electric motor with a gear-box may be necessary. The dog transmits rotation but allows vertical movement. Electric motors (15) also actuate the two valves. The apparatus has threaded orifices (16) allowing dissimilar tubing (17) to be connected to the apparatus. Fluid-tight joints are achieved using ferrules or olives (18).

Figure 6 shows an alternative embodiment, which uses pinch valves (19) instead of rotary barrel valves. At each valve the tubing can be closed by compressing with a pair of clamps (20), here shown as rods (viewed end on) A screw (21) moves one of each pair of clamps. The screw is turned by an electric motor (15). To facilitate assembly, the body of the apparatus can advantageously be split along the line A-A'.

Since flexible tubing must be used with the pinch valves, this tubing can advantageously be surrounded with inflexible tubing (28) to prevent the expansion of tubing after it leaves the body of the apparatus.

Such expansion might result in inaccurate pumping or dispensing.

Figure 7 shows a convenient method and assembly for dispensing fluid using the apparatus. The assembly comprises a dispensing nozzle (23) that is connected to the apparatus (PI). The apparatus is placed downstream of a priming pump (P2). The priming pump can pump large volumes faster than the apparatus, but is not accurate. The priming pump can be any conventional pump, such as a centrifugal, peristaltic, gear or piston pump. The priming pump is placed downstream of a reservoir (22) of the solution to be dispensed A conduit (25) with a valve (27) is also connected between the apparatus and the reservoir, in parallel with the priming pump. The method of using the assembly shown in figure 7 includes the following steps : 1. The dispensing nozzle is placed over a waste container (not shown).

2. Valve (27) opens and at least one of the valves in the apparatus (PI) closes.

3 The priming pump P2 pumps fluid through the valve (27) and conduit (25) until both are filled with fluid.

4. Valve (27) closes and both of the valves of PI open.

5. The priming pump P2 operates until fluid comes out of the dispensing nozzle (23) into the waste container. P2 then stops.

6. Valve (27) opens, and PI operates to prepare the system for accurate dispensing 7 PI stops, the dispensing nozzle is moved over the target sample vessel (24), and fluid is dispensed by further operating PI Many useful variations of this method and assembly exist. For example : I. The valve (27) can be replaced with a narrow-bore tube that runs in parallel to P2. This tube provides enough resistance to the rapid pumping of P2 to cause fluid to pass through the apparatus PI during priming, but it allows PI to draw fluid from the reservoir (26) as required 2. Pump P2 can be of a type that does not prevent flow when it is inactive In this case conduit (25) and valve (23) are not required.

3. Pump P2 can be a finger-pump, a delta-pump or a peristaltic pump, and the apparatus can be of the type that has only one valve located upstream of the dispensing chamber (described above). Again, conduit (25) and valve (23) are not required.

Claims

Claims 1 An apparatus for pumping fluids comprising two valves situated upstream and downstream of a tube that passes through a sealed chamber, which chamber is otherwise completely filled with incompressible material, said chamber also possessing a means of moving said incompressible material thereby compressing said tube, which action pumps the fluid in said tube.
2 An apparatus as claimed in claim 1 in which said means of moving the incompressible material is a means of reducing said chamber's volume.
3. An apparatus as claimed in claim 1 in which said means of moving the incompressible material is a means of introducing into said chamber more incompressible material.
4. An apparatus as claimed in any of claims 1 to 3 in which said incompressible material is a liquid or gel.
5. An apparatus as claimed in any of claims I to 3 in which said incompressible material is an elastic solid.
6 An apparatus as claimed in any of claims 1 to 3 in which said chamber contains both an incompressible elastic solid and an incompressible liquid or gel.
7 An apparatus as claimed in any of claims 1 to 6 in which said valves are pinch valves, rotary barrel valves, slide valves, automatic non-return valves, duckbill valves, reed valves, valves with balls, needle valves or diaphragm valves.
8. An apparatus as claimed in any of claims I to 7 in which valves are used which prevent flow by freezing the fluid being pumped.
9 An apparatus as claimed in claim 8 in which valves are used which possess Peltier devices
10 An apparatus as claimed in any of claims I to 9 in which said tube is coiled, flattened, has an oval cross-section, or otherwise has a set on it.
11 An apparatus as claimed in any of claims I to 10 in which said valves are automatic non-return valves.
12 An apparatus as claimed in any of claims 1 to 11 in which said incompressible material is moved by a diaphragm, thereby compressing said tubing and pumping said fluid.
13. An apparatus as claimed in any of claims 1 to 11 in which said incompressible material is moved by a springy sheet, thereby compressing said tubing and pumping said fluid.
14. An apparatus as claimed in claim 11 in which the force required to bend said flexible sheet is much greater than the force required to compress said tube.
15. An apparatus as claimed in claims 11 or 14 in which said flexible sheet is moved by a profiled plate that has a convex protruding surface, which surface comes into contact with said flexible sheet.
16 An apparatus as claimed in claim 15 in which said convex protruding surface is profiled such that it mates with said flexible sheet when said flexible sheet is fully flexed
17. An apparatus as claimed in any of claims I to 11 in which said chamber possesses an inlet port and a means of introducing liquid, which liquid compresses said tubing, thereby pumping said fluid.
18. An apparatus as claimed in any of claims 1 to 11 in which said chamber possesses an inlet port and a means of introducing liquid, which liquid moves said incompressible material, thereby compressing said tubing and pumping said fluid
19. An apparatus as claimed in claims 15 or 18 in which said means of introducing liquid is a gear pump or the equivalent.
20 An apparatus as claimed in any of claims 1 to 19 in which said means of moving said incompressible material is driven by a piezo-electric device.
21. An apparatus as claimed in any of claims 1 to 20 in which said tube is connected to other tubes and conduits, where the internal dimensions of all tubes and conduits inside and outside of the apparatus change gradually as one passes along the liquid flow path.
22 An apparatus as claimed in any of claims 1 to 21 in which said apparatus is controlled by an electronic device.
23. An apparatus as claimed in any of claims 1 to 22 in which said apparatus is controlled by an electronic device that has in its memory settings which correspond to a look-up table relating movements of the apparatus to volumes of fluid pumped.

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24 An apparatus as claimed in any of claims 1 to 20 in which said means of moving said incompressible material is operated by a profiled cam.
25. An apparatus as claimed in any of claims I to 24 in which said tube containing fluid to be pumped is bent or coiled as it passes through said chamber
26. An apparatus as claimed in any of claims I to 25 in which said chamber is split into two parts along a surface which passes through the axis of said tube at the point that said tube enters and leaves said chamber.
27. An apparatus as claimed in any of claims 1 to 26 in which motors operate any of said valves and said means of moving said incompressible material
28. An apparatus as claimed in any of claims 1 to 27 in which solenoids operate any of said valves or said means of moving said incompressible material
29 An apparatus as claimed in any of claims 1 to 28 in which said apparatus is connected to flexible tubing, which flexible tubing is surrounded by inflexible tubing that prevents expansion of said flexible tubing.
30. An apparatus as claimed in any of claims 1 to 29 in which said chamber is placed upstream of a dispensing nozzle.
31 An apparatus as claimed in any of claims 1 to 30 in which said chamber is placed downstream of a second pump which is used to prime said apparatus with the fluid to be pumped, said second pump itself being downstream of a reservoir of said fluid.
32 An apparatus as claimed in claim 31 in which a conduit runs between said chamber and said reservoir in parallel with said second pump.
33 An apparatus as claimed in claim 32 in which said conduit possesses a valve
34 An apparatus as claimed in claim 32 in which said conduit has a section which impedes fluid flow sufficiently to force fluid through said chamber when said priming pump operates.
35 An apparatus as claimed in any of claims 1 to 34 that possesses only one valve, which valve is placed on upstream of said chamber.
36. An apparatus as claimed in claim 35 in which hydrostatic pressure prevents fluid from moving in the reverse direction.
37. An apparatus as claimed in claims 35 to 36 in which a small diameter conduit or a constriction, placed downstream of said chamber, discourages fluid from moving in the reverse direction.
38. An apparatus as claimed in any of claims 35 to 37 in which surface tension prevents fluid from moving in the reverse direction.
39 An apparatus as claimed in claim 35 where the apparatus is placed downstream of a pump, which might be a delta pump, a peristaltic pump or a finger pump
40. A method of pumping fluids comprising the steps of closing a valve which is upstream of a sealed chamber filled with incompressible material, through which chamber a flexible tube passes that is connected to said valve ; closing a second valve which is downstream of said chamber; compressing said tube by moving said incompressible material, thereby pumping the fluid that is in the lumen of said tube, closing said second valve ; opening said first valve; and allowing said tube to expand, thereby drawing into said tube fresh fluid to be pumped.
41. A method as claimed in claim 40 in which the direction of pumping can be reversed by swapping the roles of said valves
42. A method as claimed in any of claims 40 to 41 in which at least one of said valves is closed at all times so that at some times both valves are closed while at other times only one valve is closed, both valves never being open at the same moment.
43 A method as claimed in any of claims 40 to 41 in which each of said valves opens at essentially the same moment that the said other valve closes, so that both valves are open simultaneously for a short period.
44. A method of pumping fluids comprising the steps of compressing a tube which passes through a sealed chamber filled with incompressible material until a first automatic non-return valve which is connected to said tube closes ; continuing to compress said tube thereby pumping the fluid that is in the lumen of said tube; expanding said tube until a second non-return valve that is connected to the opposite end of said tube closes; and continuing to expand said tube thereby opening said first valve and sucking fresh fluid into said tube.
45 A method as claimed in any of claims 40 to 44 in which the movement that expels fluid from the pump is divided into many smaller movements, each smaller movement

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corresponding to a volume that is desired to be pumped, so that many volumes are dispensed without operating the valves.
46. A method as claimed in any of claims 40 to 45 in which the accuracy of pumping is increased by the following additional steps: dispensing several volumes by operating the apparatus in several small movements without operating the valves, as claimed in claim 45 ; accurately measuring the volumes dispensed in practice as a result of each movement ; using the measurements obtained to compile a look-up table; loading the look-up table into the memory of an electronic device; and making use of said look-up table to control the apparatus to with the electronic device.
47 A method as claimed in claim 46 in which a mathematical function or an algorithm is used in place of a look-up table
48. A method as claimed in any of claims 40 to 47 in which a reservoir of fluid to be pumped is placed in a pressurized container, arranged such that the pressure acts to prime the pump with fluid before accurate pumping begins.
49. A method as claimed in claim 48 in which a second pump is used to prime the apparatus provided for pumping fluid.

50 A method as claimed in claim 49 in which a second pump is used to prime the apparatus, then after priming fluid is drawn from a reservoir through a conduit that runs in parallel with said second pump.