GB2029514A

GB2029514A - Peristaltic fluid-machines

Info

Publication number: GB2029514A
Application number: GB7930290A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-08-31
Filing date: 1979-08-31
Publication date: 1980-03-19

Abstract

A pump displaces different fluids 10 through straight or helical portions of flexible tubes 7. The said portions of the tubes 7 extend through a tubular housing 6 and are squeezed against the inside of the housing by a rotor 11 rotated by a motor 2 through a shaft 3. The tubes 7 may extend straight through the housing 6 parallel (or inclined) to the rotor axis and the rotor 11 may be in the form of a screw having a helical portion 13 (or helically disposed rollers) which squeezes the tubes 7 progressively along their length as the rotor rotates. Alternatively, the tubes 7 may extend helically about the rotor axis, the tubes being squeezed progressively along their lengths by axially extending portions of the rotor, Figs. 6 and 7 (not shown). <IMAGE>

Description

SPECIFICATION Peristaltic pump Peristaltic pumps are pumps in which a fluid, usually in a liquid or paste form, is pumped through a tube by repeatedly squeezing the tube progressively along a portion of its length. Such pumps, which are self-priming if the tube is fully closed when squeezed, are very useful for pumping fluids of widely different viscosities, either intermittently or substantially continuously, over a wide range of delivery rates. Also, they have the advantage that the fluid pumped is isolated in the tube and therefore does not come into contact with any of the driving components of the pump. Consequently, a wide range of different fluids can be pumped without any particular problem, provided that the fluid does not attack the material from which the tube is made.

Conventionally, a peristaltic pump comprises a flexible tube which extends over a support surface, and a rotor which is rotated about an axis substantially at right angles to the axis of the tube and which has a number of axially extending rollers positioned eccentrically with respect to the rotor axis so that, as the rotor is rotated, the rollers successively roll along a portion of the tube while squeezing it against the support surface to produce the peristaltic pumping action.

This arrangement is of course only able to pump one fluid at a time, although by providing one or more further pumping tubes beside the first tube and lengthening the rotor so that the rollers act on all of the tubes to produce a peristaltic pumping action in each, the pump may be used to pump as many different fluids as there are tubes at the same time, either to the same or to different feed locations as required. However, the number of tubes with which such a pump can be operated successfully is very limited because the longer the rotor is made the greater is the strain which is placed on the rotor and its rollers, and the more difficult it is for the rollers to act uniformly on all of the tubes. Also, the pump quickly becomes very large.

The present invention aims to overcome these problems so that a relatively robust and compact peristaltic pump may be constructed which is capable of operating efficiently with a relatively large number of tubes at the same time.

According to one aspect of the invention, a peristaltic pump which is capable of pumping separately and simultaneously a number of different fluids comprises a rotor and a number of flexible tubes positioned circumferentially around the rotor so that they extend in substantially the same direction as the rotor axis, the rotor having at least one tube engaging portion which extends helically about the rotor axis and which, as the rotor rotates, squeezes each tube progressively along a part of its length against a support surface to produce a peristaltic pumping action in the tube.

If the rotor has only a single helical tube engaging portion, preferably it extends completely around the rotor so that it engages all of the tubes simultaneously and, during operation, the pumping action in each tube is continuous. Alternatively, if the rotor has more than one helical tube engaging portion, these are preferably arranged so that they are evenly spaced apart circumferentially around the rotor and so that adjacent tube engaging portions overlap in the circumferential direction. This will ensure that all of the tubes are engaged simultaneously and that, during operation, the pumping action in each tube is continuous.

With these arrangements, it will be appreciated that the stress placed on the rotor during operation will be substantially evenly distributed around it, and that the number of peristaltic tubes with which the pump can be operated successfully (and hence the number of different fluids which can be pumped simultaneously) is governed more by the diameter of the rotor than by its length as in the known forms of peristaltic pump. For example, if the rotor has a diameter which is equal to its length, a pump constructed in accordance with the invention may have three times as many peristaltic tubes of a given diameter than a conventional form of peristaltic pump.

Consequently, a pump having several peristaltic tubes and constructed in accordance with the invention will be much more compact, efficient, and reliable than a conventional form of pump having the same number of tubes.

Preferably the flexible peristaltic tubes extend through a tubular housing which coaxially surrounds the rotor and the inside of which provides the support surface against which each tube is squeezed by the tube engaging portion or portions of the rotor.

Usually the housing will be cylindrical and the tubes will extend through the housing adjacent its inner surface and parallel to the rotor axis. In this case, for the pump to operate efficiently in respect of each tube, the tubes should all have substantially the same outer diameter and wall thickness as each other, i.e.

such that each tube is just closed when it is squeezed against the inside of the housing by the rotor.

If it is desired that the pump should be adjustable to accommodate pumping tubes of different outer diameter and wall thickness without having to replace either the tubular housing or the rotor, the housing may be frustoconical and the rotor tapered at the same cone angle as the housing so that axial adjustment of the rotor and housing relative to each other will vary the clearance between the tube engaging portion or portions of the rotor and the inside of the housing. In this way the pump can be used with flexible pumping tubes of different outer diameter and wall thickness, although at any one time the tubes must all be of approximately the same size as each other, as in the case of a pump having a cylindrical housing as described above.

It is however possible to arrange for the pump to operate with flexible tubes of different diameter and wall thickness at the same time. For this purpose the tubular housing may be formed by a number of axially extending segments which are held together so that at least one of the segments may be moved towards or away from the rotor axis, or may simply be replaced, in order to vary the distance of its inner surface from the rotor axis according to the diameter and wall thickness of the flexible tube which is to be supported by the inner surface of the segment when the tube is squeezed by the tube engaging portion or portions of the rotor.

Preferably the pump includes means for holding each flexible tube in position in the housing whereby the tubes are prevented from being dragged in the circumferential direction as the rotor rotates. This means may comprise grooves or other suitable guides on the inner surface of the housing, but preferably comprises a pair of plates fixed one at each end of the housing, each plate having a series of apertures through which the tubes fit and by which the tubes are held relatively firmly in position at the corresponding end of the housing.

The rotor may take the form of a screw, the thread of which forms the helical tube engaging portion of the rotor. In this case the crest of the thread preferably has a curved profile.

If a rotor having more than one tube engaging portion is required, a screw having a multistart thread may be used, and as will be appreciated it will not be necessary for the pitch of each thread to be less than the length of the screw. Alternatively, a rotor having more than one helical tube engaging portion may comprise a pair of parallel support discs which are spaced coaxially apart on the rotor axis, and a number of curved members which form the tube engaging portions of the rotor and which extend helically between and are fixed at their ends to the support discs so that the members are symmetrically arranged about the rotor axis. In such a rotor the arrangement (but not the construction) of the curved members is similar to the arrangement of the cutting blades of a cylinder lawn mower.

The invention so far has been described in terms of a peristaltic pump in which the flexible tubes extend straight through the housing and are squeezed by a helical portion or portions on the rotor. However, it will be readily appreciated that an equivalent peristaltic pump having exactly the same advantages may be constructed if the flexible tubes extending through the housing are twisted slightly in a helical direction and are squeezed by a number of axially extending portions of the rotor.

According to another aspect of the present invention therefore, a peristaltic pump which is capable of pumping separately and simultaneously a number of different fluids comprises a rotor, a tubular housing coaxially surrounding the rotor, and a number of flexible tubes which are positioned circumferentially around the rotor and each of which extends through the housing from one end to the other in a helical direction about the rotor axis, the rotor having a number of axially extending tube engaging portions which, as the rotor rotates, squeeze each tube progressively along a part of its length against the housing to produce a peristaltic pumping action in the tube.

Preferably the axially extending tube engaging portions are evenly spaced apart around the rotor, and the circumferential travel of each helical flexible tube about the rotor is not less than the spacing between the tube engaging portions so that all of the tubes are engaged simultaneously and, during operation, the pumping action in each tube is continuous. Preferably there are at least three tube engaging portions.

In this second form of the invention the rotor may comprise a shaft on which the tube engaging portions are provided by a number of ribs which extend axially along the shaft.

Alternatively, the rotor may comprise a pair of parallel support discs which are arranged coaxially apart on the rotor axis, and a number of parallel members, for example rollers, which extend between and are attached at their ends to the support discs and which form the tube engaging portions of the rotor.

The housing may be cylindrical or frustoconical in shape, and is preferably provided with means for holding the flexible tubes in position in the housing in much the same way as in the first form of the invention described earlier.

The slope of the helical path of each flexible tube in the case of the second form of the invention (or indeed of the tube engaging portion or portions of the rotor in the first form of the invention) may be chosen as desired, but is preferably between 25 and 75 degrees, preferably 45 degrees, measured from a plane perpendicular to the rotor axis approximately half way along the rotor.

One problem with peristaltic pumps is that, unless some precautions are taken to reduce the friction between the peristaltic tubes and the portion or portions of the rotor which squeeze and move along the tubes to produce the pumping action, the tubes, and indeed the rotor, will tend to wear very quickly. In the case of conventional peristaltic pumps this problem is met by providing the rotor with rollers which roll along the tubes, and indeed this simple solution is easily applicable in the case of the second form of the present invention described above. In the case of the first form of the invention, rolling contact between the rotor and the peristaltic tubes may be achieved by using the form of rotor having its tube engaging portions provided by members extending helically between a pair of support discs.In this case each helical member comprises a series of wheels which are mounted side by side along the member so that each wheel is rotatable about an axis which is parallel to the rotor axis whereby, as the rotor rotates, the wheels of each member will roll across each peristaltic tube one after the other to produce the progressive squeezing of the tube.

Alternatively or additionally, the problem of wear on the flexible tubes may be alleviated by the provision of a protective flexible sleeve between the rotor and flexible tubes. In this case the tube engaging portion or portions of the rotor will rub or roll over the inside of the sleeve, which may be suitably lubricated or coated with a low friction material such as PTFE, and the sleeve remains substantially stationary with respect to the tubes. When the sleeve becomes worn, it is relatively easy and cheap to replace the worn sleeve with a new one.

Various examples of pumps in accordance with the present invention will now be described with reference to the accompanying schematic drawings, in which: Figure 1 shows the general layout of a pump in accordance with the invention and its purpose of pumping different fluids from different sources simultaneously; Figure 2 is a view illustrating the construction and operation of one example of a pump in accordance with the invention; Figure 3 is an exploded perspective view illustrating the construction of a pump housing which may be used in the example of Fig.

2; Figure 4 is a view similar to that of Fig. 2 but illustrating a different example of the pump in accordance with the invention; Figure 5 is a view showing part of the rotor of a further embodiment of the invention and illustrating its operation; Figure 6 is a view of the rotor of yet another embodiment of the present invention; and, Figure 7 is a diagrammatic plan view of a housing in which the rotor of Fig. 6 may be used and indicating the path of the flexible tubes of the pump through the housing.

With reference to Fig. 1, the peristaltic pump in accordance with the present invention comprises a base plate 1 on which is mounted a motor 2 which is arranged to rotate a drive shaft 3 through the intermediary of a gear box 4 connected to the motor 2.

The motor 2 may be an electrical motor, an air motor, or an engine as desired, and the gear box 4 is preferably an infinitely variable speed gear box so that the speed of the shaft 3, and hence the output rate of the pump, may be controlled as desired. The end of the drive shaft 3 remote from the motor 2 and the gear box 4 is supported by a bearing 5 mounted on the base plate 1. Between the gear box 4 and the end bearing 5 the drive shaft 3 passes through a cylindrical passage in a housing 6 mounted on the base plate 1, the shaft 3 carrying a rotor for rotation therewith in the cylindrical passage of the housing 6.The flexible peristaltic tubes 7 of the pump, of which there are nine shown in Fig. 1, extend through the cylindrical passage of the housing 6 between the wall of the passage and the rotor, the tubes 7 entering the passage through apertures in a retaining plate 8 fixed at one end of the housing, and leaving the passage through apertures in a further retaining plate 9 fixed at the other end of the housing 6. As can be seen from Fig. 3 the retaining plates 8 and 9 are of split construction to facilitate their assembly around the drive shaft 3, and in each case the apertures 8a, 9a are evenly spaced around a central shaft opening 8b, 9b. The apertures 8a, and 9a are sized so that each receives its flexible tube as a tight fit, and the tubes 7 are thereby retained in the required position within the passage through the housing 6.

As described earlier in the specification, the tubes 7 may either extend straight through the cylindrical passage of the housing 6 parallel to the axis of the shaft 3, or they may twist helically about the shaft axis. In the first case a rotor will be provided with one or more helically extending surfaces (for example as described in more detail later) for squeezing the tubes 7 against the side of the cylindrical passage as the rotor is rotated, and in the second case the rotor will be provided with axially extending surfaces for squeezing the tubes 7 against the inside of the housing 6.In either case the squeezing of the tubes 7 by the rotor as it is rotated will create a peristaltic pumping action in each of the tubes 7, and by connecting the tubes 7 to different fluid supplies 10 upstream from the pump the different fluids may be delivered independently of each other to wherever required at a rate determined by the parameters of the pump.

Fig. 2 illustrates diagrammatically the form of the rotor in one example of a pump in which the flexible peristaltic pumping tubes 7 extend straight through the cylindrical passage of the housing 6 parallel to the rotor axis. In the drawing only one of the flexible tubes 7 is shown for the sake of convenience and clarity. The rotor 11 comprises a cylindri cal body 1 2 having a diameter such that the clearance between it and the inside of the housing 6 is approximately equal to the outer diameter of each of the flexible tubes 7, and a helical rib 1 3 which winds nearly twice around the body 1 2 rather like a rudimentary screw thread.The rib 1 3 has a curved profile and the clearance between it and the inside of the housing 6 is approximately equal to twice the wall thickness of each tube 7. Consequently, as the shaft 3 is rotated in the direction of the arrow 14, the rib 1 3 of the rotor 11 squeezes each of the tubes 7 progressively along its length from left to right as shown in Fig. 2, thereby inducing a flow of fluid along each tube 7 as indicated by the arrows 1 5.

In Fig. 3, in addition to the construction of the tube retaining plates 8 and 9 described earlier, the construction of one form of the housing 6 is shown. The housing is formed by three longitudinally extending segments 16, 1 7 and 1 8 having arcuate inner surfaces. The segments are arranged to be bolted together so that their arcuate inner surfaces combine to form the passage through which the flexible peristaltic tubes pass around the rotor.In the present case however, while the inner surfaces of the segments 1 6 and 1 7 will be located equidistant from the rotor axis, the inner surface of the segment 18 will be located further away from the axis and will therefore accommodate a peristaltic tube 7 of greater diameter than the tubes which will pass through the housing adjacent the surfaces of the segments 1 6 and 1 7. By changing any one of the segments 16, 1 7 and 18, the sizes of pumping tubes 7 which can be accommodated may be varied.

In the example of Fig. 4 the construction illustrated is similar to that of Fig. 2 except that the passage 19 through the housing 6 is frustoconical in shape, and the rotor 20 has a correspondingly tapered body 21 and a rib 22 extending helically around the body 21 to form a correspondingly tapered screw thread.

The operation of this arrangement is identical to that of Fig. 2 except that by adjusting the rotor 20 axially relative to the housing 6 the clearance between the rotor and the wall of the passage 1 9 can be changed to accommodate flexible tubes 7 of a different size.

Fig. 5 illustrates another form of rotor 23 which may be used in a pump in accordance with the invention in which the flexible peristaltic tubes 7 (only one of which is shown) extend parallel to the rotor axis. The rotor 23 comprises a pair of spaced support discs 24 and 25 which are fixed concentrically on the drive shaft 3, and a number (in this case 4) of spindles 26 which extend helically between and are fixed at their ends to the support discs 24 and 25 so that the spindles 26 are symmetrically arranged about the drive shaft 3. Each spindle 26 carries a series of wheels or rollers 27 located side by side along the length of the spindle 26 in such a way that each wheel or roller 27 is free to rotate about an axis which is parallel to the rotor axis. In the drawing wheels 27 are shown on only one of the spindles 26 for the sake of clarity.The peripheries of the wheels 27 provide the helical surfaces of the rotor which engage the flexible tubes of the pump to produce a peristaltic pumping action, the wheels of each spindle successively rolling across each tube to squeeze it progressively along its length (as illustrated) as the rotor is rotated.

Fig. 6 illustrates a form of rotor which is designed for use with a pump in accordance with the invention in which the flexible tubes extend in a helical path about the rotor axis.

The rotor 28 of Fig. 6 is similar in construction to that of Fig. 5 except that the spindles 26a are straight and parallel to the drive shaft 3. In this case the individual wheels 27a which are rotatably mounted on the spindles 26a may, if preferred, be replaced by a single continuous roller on each spindle. Fig. 7 illustrates a possible arrangement of the flexible tubes 7 passing helically through the cylindrical housing 6 of a pump in which the rotor shown in Fig. 6 may be used. As will be seen, the travel of each tube 7 in the circumferential direction is just over a quarter of the internal circumference of the housing, i.e. just greater than the circumferential spacing between the outermost portions of the wheels or rollers as the spindles 26a.

Claims

1. A peristaltic pump which is capable of pumping separately and simultaneously a number of different fluids, the pump comprising a rotor and a number of flexible tubes positioned circumferentially around the rotor so that they extend in substantially the same direction as the rotor axis, the rotor having at least one tube engaging portion which extends helically about the rotor axis and which, as the rotor rotates, squeezes each tube progressively along a part of its length against a support surface to produce a peristaltic pumping action in the tube.

2. A pump according to claim 1, in which the rotor has a single helical tube engaging portion which extends completely around the rotor so that it engages all of the tubes simultaneously and, during operation, the pumping action in each tube is continuous.

3. A pump according to claim 1, in which the rotor has a number of similar helical tube engaging portions which are arranged so that they are evenly spaced apart circumferentially around the rotor and so that adjacent tube engaging portions overlap in the circumferential direction, whereby all of the tubes are engaged simultaneously and, during operation, the pumping action in each tube is continuous.

4. A pump according to any one of the preceding claims, in which the flexible tubes extend through a tubular housing which coaxially surrounds the rotor and the inside of which provides the support surface against which each tube is squeezed by the tube engaging portion or portions of the rotor.

5. A pump according to claim 4, in which the housing is cylindrical and the tubes extend through the housing adjacent its inner surface and parallel to the rotor axis.

6. A pump according to claim 4, in which the housing is frustoconical in shape and the rotor is tapered at the same cone angle as the housing, the rotor and the housing being axially adjustable relative to each other to vary the clearance between the tube engaging portion or portions of the rotor and the inside of the housing.

7. A pump according to claim 4, in which the tubular housing comprises a number of axially extending segments which are held together so that at least one of the segments may be moved towards or away from the rotor axis, or may be replaced, in order to vary the distance of its inner surface from the rotor axis according to the diameter and wall thickness of the flexible tube which is to be supported by the inner surface of the segment when the tube is squeezed by the tube engaging portion or portions of the rotor.

8. A pump according to any one of claims 4 to 7, in which the pump includes means for holding each tube in position in the housing whereby the tubes are prevented from being dragged in the circumferential direction as the rotor rotates.

9. A pump according to claim 8, in which the means for holding the tubes in position in the housing comprises a pair of plates fixed one at each end of the housing, each plate having a series of apertures through which the tubes fit and by which the tubes are held relatively firmly in position at the corresponding end of the housing.

10. A pump according to any one of the preceding claims, in which the rotor is in the form of a screw, the thread or threads of which form the helical tube engaging portion or portions of the rotor.

11. A pump according to claim 10, in which the crest of the or each thread of the screw rotor has a curved profile.

1 2. A pump according to claim 3 or any one of claims 4 to 9 when dependent on claim 3, in which the rotor comprises a pair of parallel support discs which are spaced coaxially apart on the rotor axis, and a number of curved members which form the tube engag ing portions of the rotor and which extend helically between and are fixed at their ends to the support discs so that the members are symmetrically arranged about the rotor axis.

1 3. A pump according to claim 12, when dependent on claim 5, in which each curved member comprises a curved spindle which is fixed at its ends to the support discs, and a series of similar wheels which are mounted side by side on the spindle so that each wheel is rotatable about an axis which is parallel to the rotor axis to provide rolling contact between the tube engaging portions and the flexible tubes as the rotor rotates.

14. A pump according to any one of the preceding claims, in which there is a protective flexible sleeve retained between the rotor and the flexible tubes so that the tube engaging portion or portions of the rotor engage the sleeve instead of the tubes.

1 5. A peristaltic pump which is capable of pumping separately and simultaneously a number of different fluids, the pump comprising a rotor, a tubular housing coaxially surrounding the rotor, and a number of flexible tubes which are positioned circumferentially around the rotor and each of which extends through the housing from one end to the other in a helical direction about the rotor axis, the rotor having a number of axially extending tube engaging portions which, as the rotor rotates, squeeze each tube progressively along a part of its length against the housing to produce a peristaltic pumping action in the tube.

1 6. A pump according to claim 15, in which the axially extending tube engaging portions are evenly spaced apart around the rotor, and the circumferential travel of each helical flexible tube about the rotor is not less than the spacing between the tube engaging portions so that all of the tubes are engaged simultaneously and, during operation, the pumping action in each tube is continuous.

1 7. A pump according to claim 1 5 or claim 16, in which the rotor has at least three tube engaging portions.

18. A pump according to any one of claims 1 5 to 17, in which the housing is cylindrical.

1 9. A pump according to any one of claims 1 5 to 17, in which the housing is frustoconical in shape and the rotor is tapered at the same cone angle as the housing, the rotor and the housing being axially adjustable relative to each other to vary the clearance between the tube engaging portions of the rotor and the inside of the housing.

20. A pump according to any one of claims 1 5 to 19, which includes means for holding each tube in position in the housing whereby the tubes are prevented from being dragged in the circumferential direction as the rotor rotates.

21. A pump according to claim 20, in which the means for holding the tubes in position in the housing comprises a pair of plates fixed one at each end of the housing, each plate having a series of apertures through which the tubes fit and by which the tubes are held relatively firmly in position at the corresponding end of the housing.

22. A pump according to any one of claims 15 to 21, in which the rotor comprises a pair of parallel support discs which are fixed coaxially apart on the rotor axis, and a number of members which extend between and are attached at their ends to the support discs and which form the tube engaging portions of the rotor.

23. A pump according to claim 22, in which each tube engaging member comprises a spindle and a roller or a series of wheels or rollers mounted on the spindle for rotation about the spindle axis.

24. A pump according to any one of claims 1 5 to 23, in which there is a protective flexible sleeve retained between the rotor and the flexible tubes so that the tube engaging portions of the rotor engage the sleeve instead of the tubes.