WO2001027474A1

WO2001027474A1 - Peristaltic pump hose

Info

Publication number: WO2001027474A1
Application number: PCT/ZA2000/000186
Authority: WO
Inventors: Richard Roy Wood; Raymond William Hinks
Original assignee: Richard Roy Wood; Raymond William Hinks
Priority date: 1999-10-13
Filing date: 2000-10-13
Publication date: 2001-04-19
Also published as: AU1107501A

Abstract

This invention relates to a peristaltic pump hose (10) which includes a length of hose (12) which is made from suitably resilient elastomeric material and a sleeve (14) of flexible reinforcing material which surrounds the elastomeric hose (12) material and extends over the length of the composite hose (10) and to a peristaltic pump including the hose. The elastomeric hose component (12) includes two diametrically opposite wall thickness reducing formations (16) which extend over the length of the hose (12) and the reinforcing sleeve (14) is made from a suitable woven material.

Description

PERISTALTIC PUMP HOSE

FIELD OF THE INVENTION

This invention relates to a hose for use in a heavy duty peristaltic pump for pumping a liquid and more particularly a slurry and to a pump including the hose.

BACKGROUND TO THE INVENTION

The more commonly known peristaltic or hose pumps include a pump casing which carries a cylindrical pressure ring, a resiliently deformable hose which is looped concentrically in the pressure ring between the pump inlet and outlet to which the hose ends, which extend tangentially outwardly from the loop, are connected and a rotor arrangement which is rotatable on an axis which is concentric with the pressure ring and which is adapted progressively to squeeze the hose between it and the pressure plate to force a liquid in the bore of the hose ahead of it under pressure through the hose.

Hoses for use in pumps of the above type are typically made from a rubber or like material, are circular in cross-section, are thick walled and carry reinforcing which is embedded in the hose material. The hose reinforcing in smaller bore hoses is generally composed of strong synthetic fibres which are arranged in one or more concentric layers in the wall of the hose. In larger bore hoses, for industrial application pumps, some or all of the reinforcing could be made from metal braid to contain the very high hoop stresses to which the hoses are exposed in use.

The rotors of these pumps in heavy duty industrial use consist either of a centrally driven arm which carries at its ends small diameter rollers which are rotated against the pump hose to squeeze the hose and to drive a pressure wave of liquid in the hose through the hose ahead of each of the rotating rollers or a driven drum which carries radially projecting fixed skid shoes which perform the same function as the above rollers. Other, less common types of pump may use a rotor which is caused to oscillate about a drive axis by using a cam-type mechanism. Such designs however, are not practical for use in heavy duty industrial pumping applications due to their necessity to use very large and expensive rolling bearings and sophisticated sealing arrangements to protect the expensive bearings from contamination after hose rupture occurs. There is also a need in heavy duty industrial applications to provide a means of hose compression adjustment which can be applied inexpensively and conveniently to avoid onerous maintenance procedures and production losses. This type is therefore relegated to the lower pressure, lower flow duties in medical and metering applications.

Common problems that occur in pumps of the above, and other known types of peristaltic pumps, which are used industrially are:

(a) the large amount of drive energy which is required completely to squeeze closed the bore of the reinforced thick walled pump hoses and to drag the squeeze force, particularly that generated by the skid shoes, over the length of the hose in the pump with this energy requirement being exacerbated by the length of the force arm between the roller drive shaft and the roller axles or skid shoes which are carried by the rotor. These large forces which are necessary to operate the pumps require the use of expensive and costly to run large drive and power units. Additionally, the failure rate of the expensive bearings on which the small rotor rollers are joumaled for rotation is high due to the high forces and impact loads to which the rollers are exposed in use.

(b) excessive frictional heat generation caused substantially by the rotor shoes skidding over the outer surface of the hose which is exacerbated by the disruptive movement of multiple layers of reinforcing elements within the flexile elastomer mass of the hose wall and the fluid head of pressure which exists in the hose, this necessitates a requirement for flooding of the casing with expensive cooling and lubricating mediums such as food-quality glycerine but even then, periodic cessation of pumping operations is required for heat dissipation and the cooling liquid itself creates problems of expensive shaft and casing seals being utilised to prevent its leakage. Furthermore, hose failure causes contamination of the lubricant which then necessitates disposal and refilling of the casing and invariably, replacement of bearings and other close- clearance pump components. The high heat generation may in higher duty applications, adversely affect the efficiency of the pump as a result of having to lower the pump speed and therefore the flow, in order to avoid the need to stop for cooling. In these circumstances, the selection of a larger than necessary pumping unit may be necessary.

(c) short hose life caused principally by the large squeeze forces, which are necessary completely to close the hose bore, excessively stretching the thick walled reinforced elastomeric material to sharp radius curves along the outer edges of the hose as it is repeatedly flattened by the small diameter rotor rollers or shoes in operation. This large degree of stretch around particularly the outer zone of the sharp curves, causes fatigue of the hose elastomer in these zones with consequential tearing from the outer surface of the hose in the sharp curves and eventual catastrophic failure of the hose.

(d) yet further problems with conventional pumps are caused by the circumferentially discontinuous nature of the hose within the casing structure which results in destructive rapidly repeated, heavy impacts of the multiple shoes or small rollers against the hose where it enters the casing. In the case of fixed shoe machines particularly, these impacts not only cause premature fatigue of the hose rubber inlet zone but additionally attempt to pull the hose from its suction-side fixture mechanism and induces a propensity for rubber creep to occur as the shoes are forcibly driven into and along the highly resistive liquid filled reinforced hose structure. The impact shocks additionally induce sharp high amplitude hydraulic pulses to occur in the hose which are detrimentally transmitted to connecting pipework and to the pump mounting structures as well as to the bearings which support the rotor. In such pumps also, it is necessary to lead the hose tangentially into the casing at both the inlet and outlet positions to moderate the angle of impingement of the shoes on the hose as far as possible. This then encourages a long compressive dwell period at the suction position which causes a consequential back-pulse into the suction line and disrupts the smooth flow of the suction fluid into the hose.

SUMMARY OF THE INVENTION

A peristaltic pump hose according to the invention includes a length of hose which is made from suitably resilient elastomeric material and a sleeve of flexible reinforcing material which surrounds the elastomeric hose and extends over the length of the composite hose. The elastomeric hose material is conveniently an unreinforced rubber or like material. In its preferred form the reinforcing sleeve is made from a suitable woven material. The weave of the woven material of the sleeve is preferably a circular weave.

The circular weft thread of the weave of the sleeve material may be made from or include a high tensile substantially non-extensible material such as kevlar fibre, carbon fibre, boron fibre or the like. The warp threads of the weave may similarly be made from or include high tensile substantially non-extensible materials such as kevlar fibre, carbon fibre, boron fibre or the like.

The wall thickness on opposite sides of the elastomeric hose component, in a direction normal to the direction of applied compressive pressure to the hose in a pump in which the hose is intended for use, preferably is less than that of the remainder of the hose component. The reduction in the wall thickness of the elastomeric hose component may be provided by diametrically opposite groove formations in the outer surface of the wall of the hose component which extend over the length of the hose component.

Preferably the elastomeric hose component is cured into the form of a single loop helix the diameter of which is compatible with the pump casing in which the hose is to be used with at least the outlet end portion of the hose extending tangentially from the loop. The inlet portion of the hose component may project non-tangentially outwardly from the hose loop. Preferably the hose includes a suitable low-friction lubricant between the outer surface of the elastomeric hose component and the inner surface of the reinforcing sleeve.

The hose sleeve may conveniently be impregnated with a suitable flexible plastic polymer such as polyurethane, polyvinyl chloride or the like.

A peristaltic pump according to the invention includes a pump casing, a cylindrical pressure ring in the casing, a pump hose as described above which is looped in and around the pressure ring with its open ends connected to inlet and outlet ports from the casing, a rotor in the pressure ring which is adapted progressively to squeeze the hose between it and the pressure ring to force liquid which is drawn into the hose from the inlet port through the hose and from the outlet port as it is rotated in the casing and means for rotating the rotor in the casing.

The rotor of the pump may be cylindrical and conveniently have an outer diameter which is greater than half the diameter of the inner surface of the pressure ring and less than the inner surface diameter of the unsqueezed hose loop when against the pressure ring.

The pump rotor rotating means may be a drive shaft which passes through a wall of the casing concentric with the inner surface of the pressure ring and a crank arrangement which is fixed to the drive shaft and carries the rotor progressively to squeeze the hose between it and the pressure ring as it is orbitally rotated by the crank arrangement in the casing.

The pump may include means for adjusting the outer surface of the rotor towards and away from the pressure ring.

The end portion of the hose which is connected to the outlet port from the casing may be tangential to the hose loop and the other end portion of the hose which is connected to the inlet port into the casing may be non-tangential to the hose loop. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example only with reference to the drawings in which:

FIGURE 1 is a perspective view of the elastomeric hose component of the pump hose of the invention,

FIGURE 2 is a half-sectioned side elevation of a fragment of a length of the hose of the invention,

FIGURE 3 is an end elevation of the Figure 2 hose,

FIGURE 4 is a sectioned end elevation of the hose shown flattened as it would be in a pump in use, hatching is omitted from the drawing for clarity,

FIGURE 5 is a partially sectioned side elevation of the peristaltic pump of the invention, and

FIGURE 6 is an end elevation of the Figure 5 pump shown sectioned on the line 6-6 in Figure 5.

DETAILED DESCRIPTION OF THE INVENTION

The peristaltic pump hose 10 of the invention is shown in Figures 1 to 4 to consist of a length of rubber hose 12 which is sheathed in a protective sleeve 14 of woven reinforcing material.

The hose 12 is made from a totally unreinforced natural rubber or a rubber compound such as siiicone, EDPM, nitrile and the like which is suitable for and non reactive with the liquid which is to be pumped through it in use. For example if the liquid to be pumped through the hose is or contains oil nitrile rubber would be used in the manufacture of the hose.

The uncured rubber or rubber compound of the hose 12 is, in manufacture, extruded to the required length for a specific pump and cross-sectional shape, as shown in Figure 3, which, in this embodiment of the invention, is circular and includes two diametrically opposite stress relief groove formations 16 which extend over the length of the hose.

The uncured hose is located in a jig to hold it in the configuration illustrated in Figures 1 and 5 and the rubber of the hose is then cured in the conventional manner to set the single helix shape shown in the drawings and to obtain the required Shore hardness of the rubber. It is critically important to the invention that the hose stress relief formations 16 in the shaped hose are situated exactly at the cross-sectional ends of the hose as the hose is flattened to the shape shown in Figure 4 by a pump rotor in use.

The outlet end 18 of the hose, as shown in Figures 1 and 5, leaves the hose helix loop tangentially and the inlet end is angled into the loop at an angle of about 40°.

The sleeve 14 is woven in a manner and from materials which will provide the composite hose 10 with more than adequate hoop strength to contain the high radial forces which are generated in the hose, in use, in specific applications. In the preferred form of the invention the sleeve is a finely woven circular weave with the warp threads of the weave lying in the axial direction of the sleeve and the substantially continuous weft thread in a circular almost normal direction to the warp threads to weave optimise the hoop strength of the sleeve.

It is important to the invention that the fibrous threads from which the sleeve 14 is woven are substantially inelastic to inhibit both longitudinal and radial expansion of the elastomeric hose 12 in use. Suitable thread materials are polyester or polypropylene fibres which could be supplemented with or replaced by threads of high tensile material such as fibres of kevlar, carbon, boron and the like. The sleeve material is impregnated with a flexible plastic polymer such as polyurethane, polyvinyl chloride or the like to prevent liquid leakage from the sleeve in the event of a ruptured hose 12 and to set the weave pattern of the material against pressure and frictional displacement in use. Prior to curing of the plastics material the elastomeric hose 12 is coated with a suitable release agent and the sleeve is slid over the hose component 12 to be in intimate contact or nearly so with the outer surface of the hose. The release agent is important for two reasons; firstly to facilitate the location of the sleeve 14 on the hose 12 and secondly and more importantly to ensure that the sleeve is free of the outer surface of the hose to permit a small degree of slip between the hose and its protective sleeve without generating any shear force between the two hose components in use.

In use, in a peristaltic pump, the hose 10 is progressively squeezed over its length from the Figure 3 circular open configuration to the flat closed configuration of Figure 4 by the pump rotor to force liquid in the hose ahead of the rotor through the hose. As mentioned above and further described below it is important that the hose 10 is arranged in the pump casing for a diametrical line through the two stress relief grooves 16 to be normal to the compressive squeeze forces applied to the hose, as shown by the arrows in Figure 4, to ensure that the grooves are situated exactly at the ends of the flattened hose as shown in Figure 4.

The purpose of the stress relief grooves 16 is to eliminate the high degree of circumferential stretch stress which would otherwise be imposed on material in the groove space as the hose is flattened to its Figure 4 configuration and for the elastomeric material between the inner surface of the hose 12 and the bases of the grooves 16 to serve as relatively unstressed hinges 17 during repeated flattening of the liquid filled hose in use. Prior to the hose being fully flattened the hinge 17 material is pressed outwardly from the hose bore into the space occupied by the grooves 16 and into contact with the restraining sleeve 14, as shown in Figure 4. The portions of the hose on either side of the hinges are, on the application of rotor pressure, flattened, as shown in Figure 4, with the hinged ends of the hose pressed under little stress fully up against and supported by the sleeve 14. This hinge effect not only prolongs the integrity of the hose material in the groove zones but additionally results in far less compressive force being required to flatten the hose to close its bore than that which is required to close the bore of an annular reinforced hose. The arch effect of the arcuate hose sections above and below the grooves 16 acting on one another ensures the rapid return of the thick walled hose to its circular from its flattened configuration when the compressive rotor force on it is removed. The return to round of the hose creates a negative pressure in the hose which provides the inlet suction characteristics of the pump. It is important that the base portion of the groove formations and the transition zones of the hose 12 from the base of the grooves 16 to the outer surface of the hose are smoothly rounded to prevent the hose material from scuffing on the inner surface of the sleeve as it is flexed in the sleeve.

The peristaltic pump of the invention is shown in Figures 5 and 6 to include a pump casing 19 which includes an outer wall fixed pressure ring 20, a drive shaft 22, a crank arrangement 24, a rotor 26, the hose 10 of the invention and a drive arrangement indicated generally at 28.

The pump casing includes inlet and outlet ports 30 and 32 respectively which pass through the casing wall pressure plate 20, a boss in which the drive shaft 22 is journaled for rotation on suitable bearings, as shown in Figure 6, and a front cover plate 34.

The pump casing cover plate 34, in this embodiment of the invention, is removable and is made from a heavy clear glass to enable the complete inner workings of the pump easily to be visually monitored in use. The cover plate, could of course, be made from metal and include a glass observation window.

The crank arrangement 24 includes a disc shaped crank arm 36 which is integral with the drive shaft 22 and a crank pin 38 which is fixed to and projects from the arm. The crank pin 38 carries an eccentric sleeve 40 to which an adjustment nut 42 is fixed. The sleeve 40 is releasibly located on the crank shaft 38 by a bolt 44. The sleeve 40 carries bearings, as shown in Figure 6, on which the rotor 26 is journaled for rotation. The purpose of the eccentric sleeve 40 is, by rotation on the crank pin 38, conveniently to enable the radially outer surface of the rotor in the casing to be moved towards and away from the pressure ring 20 for insertion of the hose 10 into the casing during repair or maintenance and to adjust the rotor pressure on the hose.

Since the pumping action of the pump is in the form of positive displacement, any blockage of the discharge piping which leads from the pump would cause an immediate pressure build within the hose element which may be of a magnitude which cannot be resisted by the circular hoop containment of the outer sheathing element of the hose. To avoid a catastrophic pressure build in such circumstance, the eccentric adjustment sleeve 40 may be fitted with a spring bias mechanism, not shown, which enables forced movement of the rotor to provide automatic flow relief when an internal hose pressure creates a force which exceeds the opposing, pre-set spring force.

During assembly of the pump the hose 10, which, as described above, has been preformed to be a neat fit in the casing 19, is located in the casing with its radially outer surface on or adjacent the inner surface of the pressure ring 20 and its inlet and outlet ends 20 and 18 in the casing inlet and outlet ports 30 and 32, as shown in Figure 5.

Any convenient arrangement could be employed to anchor the hose ends in the flange ports of the pump casing. An example of the preferred anchor arrangement is shown in Figure 5 to consist of a tapered spigot or thimble 48 which has a serrated outer gripping surface which, on insertion into a hose end, squeezes and wedge-locks the mouth portion of the hose between it and a tapered surface of the port mouth. With this anchor arrangement the ends of the sleeve over the spigot are longitudinally slit to accommodate the necessary increase in radial dimension of the sleeve over the spigot 48. The outer end of the spigot carries a radial flange 49. The ends of the sleeve 14 are located between the flanges 49 and the inlet and outlet pump flanges and are positively clamped in this position when the supply and delivery pipe flanges are bolted to the pump flanges. As mentioned above, it is highly important to the successful operation of the pump that the hose 10 is installed in the casing with both of its stress relief groove formations 16 lying in alignment in the axial direction of the casing and parallel to the surfaces of the pressure ring 20 and the rotor 26 as shown in Figure 6.

The sleeve 40, with the rotor 26 mounted on it, is now located over the crank shaft 38 and rotated to bring the outermost surface of the rotor into the desired pressure contact with the hose and at which pressure the hose is squeezed completely closed between the pressure ring 20 and the rotor as shown in Figures 4, 5 and 6.

In use, the required pipe lines are connected to the casing 19 inlet and outlet port flanges and the inlet port 30 is flooded with liquid to be pumped. A motor 50 of the drive arrangement 28 is now activated to drive a gearbox 52 which is connected to the pump drive shaft 22 to cause rotation of the crank arrangement and so the rotor 26 in the pump casing 18 at the desired speed of rotation of the pump.

As the external contact area of the relatively large diameter rotor 26 on the hose 10 is moved in an anti-clockwise direction in the casing by the crank driven rotor progressively to squeeze the hose, by pressure in a predominantly radial direction, against the pressure ring 20 a negative suction pressure is generated in the hose between the port 30 and the advancing hose squeeze to entrain inlet liquid through the hose behind the moving rotor 26. When the hose squeeze zone reaches the inlet end 20 of the hose 10 the relatively sharply angled inlet end of the hose is closed rapidly by the radial pressure of the rotor on it to minimise the back pulse duration in the inlet port 30. Liquid in the hose ahead of the squeeze zone of the rotor is simultaneously pumped from the outlet port into the delivery line attached to it with minimal pulse disruption of the delivered liquid. Whatever pulse disruption exists in the delivered liquid from the pump is further minimised by the inlet and outlet hose overlap in the hose loop at the bottom of the casing which ensures that the hose 10 always contains a full charge of fluid under positive suction-head conditions and to smooth the delivery of the hose contents as the pressure wave, which is induced into the charge of fluid within the hose by the continuously advancing compressive squeeze force, will be continuous. A most important feature of the pump of the invention is that as no meaningful friction generating relative movement exists during operation of the pump between the outer surface of the hose 10 and the pressure ring and the rotor surfaces no power consuming heat generating or hose elongation drag contact will be imposed on the hose wall as the hose 10, as mentioned above, will see compressive force on it in very nearly only a purely radial direction. The power requirement of the pump is further reduced by the short length of the force arm, in this case, the distance A between the centre-lines of the drive shaft 22 and the crank arm 36, as shown in Figure 6, which is required to rotate the crank arm. These features together with the relatively low force required adequately to squeeze the hose 10 makes it possible for a pump of the invention to be half the size and run at double the speed of rotation of a conventional peristaltic pump while providing the same liquid delivery, less power consumption and little meaningful heat generation and vibration.

The invention is not limited to the precise details as herein described. For example, where large loads are to be experienced by the pump of the invention, as will arise in pumping viscous slurries, it will probably be necessary to support the crank pin, or one like it, on both sides. In this event the casing cover plate 34 will be made from metal and carry a boss in which a support shaft, opposite and in axial alignment with the drive shaft, will need to be rotatably supported to carry a second crank arm 36 which is connected to the free end of the crank pin 38. With this arrangement the crank pin 38 will need to be made to be movably adjustable on its crank arms to enable the radial position of the rotor to be adjustable relatively to the pressure ring 20. Additionally, the hose 10 need not necessarily be circular in cross-section and the thinning of opposite side walls of the elastomeric hose component 12, to provide the hose fold hinges, could be achieved by merely flattening the opposite side wall portions of the hose or by suitable opposite groove-like formations which are shaped other than those illustrated in the drawings.

Claims

1. A peristaltic pump hose including a length of hose which is made from suitably resilient elastomeric material and a sleeve of flexible reinforcing material which surrounds the elastomeric hose material and extends over the length of the composite hose.

2. A peristaltic pump hose as claimed in claim 1 wherein the elastomeric hose material is an unreinforced rubber or like material.

3. A peristaltic pump hose as claimed in either one of claims 1 or 2 wherein the reinforcing sleeve is made from a suitable woven material.

4. A peristaltic pump hose as claimed in claim 3 wherein the weave of the woven material of the sleeve is a circular weave.

5. A peristaltic pump hose as claimed in claim 4 wherein the circular weft thread of the weave is made from or includes a high tensile substantially non-extensible material such as kevlar fibre, carbon fibre, boron fibre or the like.

6. A peristaltic pump hose as claimed in either one of claims 4 or 5 wherein the warp threads of the weave are made from or includes high tensile substantially non- extensible materials such as kevlar fibre, carbon fibre, boron fibre or the like.

7. A peristaltic pump hose as claimed in any one of the above claims wherein the wall thickness on opposite sides of the elastomeric hose component, in a direction normal to the direction of applied compressive pressure to the hose in a pump in which the hose is intended for use, is less than that of the remainder of the hose component.

8. A peristaltic pump hose as claimed in claim 7 wherein the reduction in the wall thickness of the elastomeric hose component is provided by diametrically opposite groove formations in the outer surface of the wall of the hose component which extend over the length of the hose component.

9. A peristaltic pump hose as claimed in any one of claims 1 to 8 wherein the elastomeric hose component is cured into the form of a single loop helix the diameter of which is compatible with the pump casing in which the hose is to be used with at least the outlet end portion of the hose extending tangentially from the loop.

10. A peristaltic pump hose as claimed in claim 9 wherein the inlet portion of the hose component projects non-tangentially outwardly from the hose loop.

11. A peristaltic pump hose as claimed in any one of the above claims including a suitable low-friction lubricant between the outer surface of the elastomeric hose component and the inner surface of the reinforcing sleeve.

12. A peristaltic pump hose as claimed in any one of claims 3 to 11 wherein the hose sleeve is impregnated with a suitable flexible plastic polymer such as polyurethane, polyvinyl chloride or the like.

13. A peristaltic pump including a pump casing, a cylindrical pressure ring in the casing, a pump hose as claimed in any one of claims 1 to 12 which is looped in and around the pressure ring with its open ends connected to inlet and outlet ports from the casing, a rotor in the pressure ring which is adapted progressively to squeeze the hose between it and the pressure ring to force liquid which is drawn into the hose from the inlet port through the hose and from the outlet port as it is rotated in the casing and means for rotating the rotor in the casing.

14. A peristaltic pump as claimed in claim 13 wherein the rotor is cylindrical and has an outer diameter which is greater than half the diameter of the inner surface of the pressure ring and less than the inner surface diameter of the unsqueezed hose loop when against the pressure ring.

15. A peristaltic pump as claimed in either one of claims 13 or 14 wherein the rotor rotating means is a drive shaft which passes through a wall of the casing concentric with the inner surface of the pressure ring and a crank arrangement which is fixed to the drive shaft and carries the rotor progressively to squeeze the hose between it and the pressure ring as it is rotated by the crank arrangement in the casing.

16. A peristaltic pump as claimed in claim 15 wherein the crank arrangement includes a crank arm which is fixed to the drive shaft and a crank pin on which the rotor is rotatable and which is fixed to the crank arm with its axis parallel to and radially spaced from the drive shaft axis.

17. A peristaltic pump as claimed in claim 16 including an eccentric sleeve which is rotatable on the crank pin for adjusting an outer surface portion of the rotor towards and away from the pressure plate, at least one roller bearing between the outer surface of the eccentric sleeve and the inner surface of the central bore of the rotor and means for releasibly locking the eccentric sleeve to the crank pin.

18. A peristaltic pump as claimed in any one of claims 13 to 17 wherein the outer ends of the casing inlet and outlet ports are flanged with the mouths of the ports from the flanges being inwardly tapered and the pump includes tapered spigots which are pressed into the hose ends in the ports to compress and lock the hose ends in the ports between their tapered outer surfaces and the inner tapered surfaces of the ports.

19. A peristaltic pump as claimed in claim 18 wherein the outer tapered surfaces of the hose locking spigots are circumferentially serrated.

20. A peristaltic pump as claimed in either one of claims 18 or 19 wherein the outer ends of the hose sleeve are longitudinally slit and folded radially outwardly onto the pump casing flanges and the hose locking spigots carry radial flanges on their outer ends for clamping the ends of the hose sleeve between them and the casing flanges, in use.

21. A peristaltic pump as claimed in any one of claims 13 to 20 wherein the end portion of the hose which is connected to the outlet port from the casing is tangential to the hose loop.

22. A peristaltic pump as claimed in claim 21 wherein the end portion of the hose which is connected to the inlet port into the casing is non-tangential to the hose loop.