WO1996031269A1

WO1996031269A1 - Peristaltic fluid pumping and/or sludge separation device

Info

Publication number: WO1996031269A1
Application number: PCT/GB1996/000859
Authority: WO
Inventors: David Arthur Hoare
Original assignee: Albury Bourne Ltd.
Priority date: 1995-04-07
Filing date: 1996-04-04
Publication date: 1996-10-10
Also published as: AU5283196A; GB2299524A8; CA2216561A1; TR199701123T1; GB9607258D0; JPH11503803A; GB9507311D0; EP0819023A1; GB2299524A

Abstract

A method and apparatus for pumping fluids, for evacuating a vessel and for filtering a mixture of fluids and solids. The apparatus comprises a housing, a rotor cage having free running rollers arranged around the circumference of the cage, and tubing arranged around the cage. The tubing is of two types, one for evacuating the vessel. The second which is of lay flat construction for performing the filtering of the mixture of fluids and solids by forcing the liquid out from the liquid/solid mixture by means of squeezing and expansion of the tubing; the method and apparatus utilise peristaltic principles.

Description

PERISTALTIC FLUID PUMPING AND/OR SLUDGE SEPARATION DEVICE.

The present invention relates to a method and apparatus for the pumping of fluids and, more particulary to the processing of mixtures of liquids and solids. For example, the invention can be used to separate liquids and solids in sludges, such as sewage sludges and agricultural slurries or in foodstuffs.

The method and apparatus can be used for the processing of waste water or waste liquids, carrying solids or particulate matter in any proportion. For example, the invention can be used for the dewatering of animal slurries, for the treatment of the liquid effluent from a vegetable washing plant, or the treatment of the liquid effluent from poultry packing plants, dairies and creameries and cheesemaking factories. It can also be used for treating industrial, municipal and commercial waste liquids, municipal sewage sludges including digested and non-digested primary and secondary sludges, industrial sludges such as paper and asbestos like plant waste sludges and any other waste sludges and mixtures thereof.

Furthermore, the invention can be used for the extraction of juices from citrus fruits and other fruit products such as currant and apple pulp, or even for separating the juice and fruit flesh from the pips, stalks, branches and leaves during the harvesting of grapes and blackcurrants.

By separating solids from liquids in solid/liquid mixtures, this facilitates the handling, transporting and use or dispersal of the residue solids and liquids.

According to one aspect of the present invention, we provide a method of separating solids from liquids in a mixture of liquids and solids, comprising the steps of pumping the mixture through a composite tube having an internal tube portion formed of filtering material, and surrounding the internal tube portion, an external tube portion of impervious material, wherein the mixture is fed to an inlet end of the internal portion, which is of larger cross sectional area than an outlet end thereof, thus causing liquid to be forced through the filtering material, and into the space between the internal and external tube portions, and causing the said liquid to pass through at least one liquid outlet from said space, and causing the solids to be forced through the outlet of the internal tube portion.

Preferably, the external tube portion tapers and is of the same cross sectional area, e.g. diameter as the internal tube portion at its inlet end, but at the outlet end thereof, is of greater cross sectional area, e.g. diameter, and communicates with two liquid outlets. Preferably the tube portions are made up of circular lay-flat tubing.

Preferably, the mixture is pumped through the composite tube by entraining the composite tube, preferably under tension, around a rotary cage having rollers on its surface, and causing the cage to rotate so that it forces pockets of the mixture along the tube from its inlet and to its outlet end, using peristaltic principles.

Also according to this aspect of the invention, we provide apparatus for separating solids from liquids in a mixture of solids and liquid, comprising a composite tube having an internal tube portion formed of filtering material and an external tube portion, surrounding the internal tube portion, and made of an impervious material, wherein the internal tube portion has an inlet end of larger cross sectional area than an outlet end thereof, and pump means for forcing the mixture through the composite tube, whereby solids are pumped from the inlet end of the internal tube portion and out of the outlet end, whereas liquids are forced through the filtering material and out of an outlet of the external tube portion. Preferably, the external tube portion is connected at one end thereof to the inlet end of the internal tube portion and at the opposite thereof to the outlet end of the internal tube portion, with its outlet being located adjacent this end of the tube portion. Preferably, the external tube portion has a larger cross sectional area at its end connected to the outlet end of the internal tube portion. Preferably, at the outlet end of the internal tube portion, a plate is provided having a central aperture therein to which the outlet end of the internal tube portion is connected, and the outlet end of the external tube portion is also connected to the plate, there being at least two outlets for the external tube portion also provided in the plate.

Preferably, the apparatus includes a rotary cage having rollers on its periphery, the axes of which are parallel to the rotary axis of and circumferentially spaced around the periphery of the rotary cage, and the composite tube is entrained under tension with its inlet and outlet ends held stationary, around part of the periphery of the cage, so that when the cage is rotated, mixture located in the composite tube will be forced through the tube using peristaltic principles.

Preferably, the cage and composite tube are located in a housing having an arcuate wall portion (which preferably is part cylindrical and concentric with the said rotary axis) and two end walls in which end walls the cage is journalled for rotation about said axis, but of slightly smaller radius than that of the arcuate wall portion, and the composite tube is sandwiched between the rotating cage and arcuate wall portion.

According to a further aspect of the present invention, we provide a peristaltic pump comprising a rotary cage having rollers en a surface thereof, and a fluid tight housing having an arcuate wall which is preferably part cylindrical and concentric with a rotational axis of the cage, but having a marginally larger radius than that of the arc subtended by the rollers when the cage is rotated, and a lay flat tube entrained over at least some of the rollers of the cage, so as to extend between the said rollers and the arcuate wall of the housing, one end of the lay flat tube being connected to an outlet in a wall of the housing, and an opposite end thereof being connected to an inlet in a wall of the housing, there being a non return valve in the outlet to prevent fluid from entering the housing, and wherein means is provided to reduce the pressure within the housing to cause the lay flat tube to expand from its lay flat state into a tubular state.

Also according to this further aspect of the present invention, we provide a method of pumping peristaltically, comprising the steps of: locating a lay-flat tube within a housing, connecting one end of the tube to an inlet in a wall of the housing and connecting an opposite end of the tube to an outlet in the wall of the housing, and locating a central region of the lay-flat tube so that it extends around a part of cage rotatable in the housing and between rollers supported on the periphery of the cage and an arcuate wall of the housing which wall is concentric with the rotational axis of the cage, and causing said cage to rotate whereby fluid within the lay-flat tube is forced along the tube from the inlet to the outlet as the rollers rotate around the rotational axis of the cage, and subjecting the interior of the housing to a pressure which is less than that surrounding the housing to cause the lay- flat tube to be inflated with the fluid to be pumped.

Preferably the radius of the internal periphery of the arcuate wall of the housing is only marginally larger than the radius of an arc subtended by a surface of the rollers when the cage is rotated so that there is just sufficient room for the lay-flat tubing to be located between the two arcuate surfaces. Alternatively, the spacing between the two arcuate surfaces nay be somewhat larger, in which case the lay-flat tubing is entrained around the cage under tension.

Preferably, the rollers are supported for rotation about their longitudinal axes between parallel spaced end walls of the housing. Preferably, the spacing of the rotational axes of the rollers from the rotational axis of the cage is adjustable.

According to a third aspect of the present invention, we provide an apparatus for creating a pressure within a housing which is less than the external pressure surrounding the housing, using peristaltic pumping principles, said apparatus comprising a closed housing having a side wall at least part of which is arcuate, and preferably cylindrical, and a pair of spaced opposed end walls connected by said part arcuate side wall, a cage rotatable within the housing, the cage having rollers spaced around its periphery and a lay-flat tube extending around the cage and located between the peripheries of the rollers and the internal surface of the part cylindrical side wall, one end of the lay-flat tube being connected to an outlet in a wall of the housing and the opposite end of the lay-flat tube being connected to a perforated rigid member fixedly secured within the housing, and means to cause rotation of the cage such that air within the housing will be drawn through the perforations in the rigid member and pumped along the tube in peristaltic manner from the perforated member and through the outlet, there being a non-return valve located in the tube or outlet to prevent air vented from the apparatus or air surrounding the housing from re-entering the tube, whereby the pressure within the housing is reduced relative to that around the housing.

Also according to this aspect of the invention, we provide a method of reducing the pressure of a fluid within a closed housing, comprising the steps of: forming the housing with a part arcuate side wall, causing a rotor within the housing to be rotated so that rollers located at its periphery define a cylindrical arc spaced from but generally parallel to the internal surface of the part arcuate side wall, entraining a lay-flat tube around the cage over the rollers so that the tube is located between the rollers and the part arcuate side wall, securing an outlet end of the tube to an outlet in a wall of the closed housing, providing a non-return valve in the outlet or the tube, securing an opposite end of the tube to a rigid perforated member fixedly secured within the housing, and causing the cage to rotate so that fluid from within the interior of the housing and passing into the interior of the lay-flat tube through the perforated member is pumped in peristaltic manner through the tube and out of the outlet, thereby reducing the pressure of the fluid within the housing relative to that surrounding the housing.

Preferably, the arcuate part of the side wall of the housing is semi-cylindrical and closely spaced from and parallel to the arc defined by the rotating rollers.

Alternatively, the side wall of the housing may be cylindrical, in which case it is not essential for the lay- flat tube to be closely sandwiched between the rollers and the internal surface of the housing, but in this instance it is preferred that the lay-flat tube is entrained under tension over the rollers on the cage.

Preferably, the method of and apparatus for separating solids from liquids in a mixture of liquids and solids as described above and the peristaltic pump and method of pumping peristaltically as described above, and the apparatus for and method of reducing the pressure of a fluid in a housing are combined in a single apparatus, the operation of which can perform all three methods together. This apparatus incorporates a single cage with rollers within a single housing and located within the housing around the cage are at least two lay-flat tubes, one for generating the reduced pressure within the housing and the other incorporating the composite tube so that both tubes are caused to inflate as a result of the reduced pressure being generated within the housing by the one tube and at the same time the other tube allows the peristaltic pumping and separation to occur, there being a single power source to cause rotation of the cage.

Other preferred features of the methods and apparatuses described above will become apparent from the description with reference to drawings which follows herein.

The present invention is now described by way of example with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view of a preferred embodiment of a pumping unit.

Figure 2 is a plan view of a preferred rotor cage.

Figure 3 is a diagrammatic section of the pumping unit of figure 1 through an evacuating pipe.

Figure 4 is a diagrammatic section of the pumping unit of figure 1, through a filtering pipe.

Figure 5 is a plan view of a filtering tube.

Figure 6 is an outline section on line VI through the filtering tube.

Figure 7 is a diagrammatic perspective view of the pumping unit of figure 1.

Figure 8 is a perspective view of an alternative embodiment of a pumping unit.

Figure 9 is a diagrammatic perspective of the pumping unit of figure 8.

Referring to Figure 1, a pumping unit 1 has an outer housing 3 comprising a semi-cylindrical front 5, a top 7, a bottom 9, two sides 11 & 13 and a back 15. A drive motor and gearbox assembly 17 is mounted on one of the sides 11, 13 substantially aligned with the axial centre of the semi- cylindrical front 5.

The outer housing 3, and motor and gearbox assembly 17 are mounted on a framework 19. A driveshaft 31 protruding into the interior of the outer housing 3 along the axis of the motor and gearbox assembly 17 is supported within the housing 3 by a bearing assembly (not shown) . The bearing assembly is of an airtight design capable of maintaining a vacuum within the housing 3. The second side 13 of the housing 3 comprises a removable endplate, which when fitted to the housing 3 creates an air tight seal capable of maintaining a vacuum within the housing 3. The removable endplate is to permit the inside components of the pumping unit 1 to be serviced and/or adjusted. Onto the driveshaft, inside the housing 3, is axially mounted a cylindrical framework of members which can be described in general terms as a rotor cage 21, as shown in Figures 2-4 and 7.

The rotor cage 21 has two circular endplates 23 & 25, optionally linked by spacer bars 27 secured at intervals to the circular endplates 23 & 25. Eight bearing support channels 29 spaced at 45° intervals to the central axis of the rotor cage 21 are formed in each endplate 23 & 25 of the circular rotor cage 21, to form a bearing support star. The support channels 29 extend radially outwardly from the drive shaft 31 to adjacent the circumferential edge of the endplates 23 & 25. An adjustment means 33 is located in each channel 29. The radially outermost end of the adjustment means 33 comprises a block 35. The two endplates 23 & 25 are aligned axially so that each support channel 29 aligns with the corresponding support channel 29 in the other endplate.

Rollers 37 are fitted between the endplates 23 & 25 attached to two corresponding blocks 35 such that the ends of the rollers 37 locate within the blocks 35, and the adjustment means 33 provide adjustment for each roller 37 by changing the radial position of the blocks 35 with respect to the endplates 23 & 25. The rollers 37 can therefore be set independently to positions where all the rollers 37 protrude^' the same radial distance from the centre of the driveshaft 31. By adjusting the rollers 37 to equidistant positions from the central axis of the drive shaft 31, the rotor cage 21 rotates in balance.

The rollers 37 comprise free running cylinders extending substantially the full length of the rotor cage 21. The surface layer of the cylinders comprise a hard wearing material such as p.v.c. or nylon. The cylinders have central shafts 39, the ends of which are fitted to the blocks 35.

Referring to figures 3 to 7, there is situated between the rotor cage 21 and the internal surface 41 of the outer housing 3 , lay flat tubing comprising at least one evacuating pipe 43 and at least one filtering pipe 45. The evacuating pipe 43 comprises a length of lay flat tubing, of length longer than half of the circumference of the rotor cage 21. Attached to the inside of the back 15 of the housing 3 are a first 44 and a second 47 pipe attachment point. The first attachment point 44 comprises a perforated tube 49 extending inside the housing 3 and with which the first end of the evacuating pipe 43 is engaged so that the perforations in the tube 49 are not covered by the evacuating pipe 43. The second pipe attachment point 47 is also attached to the back 15 of the housing, but in this instance, there is a hole in the back 15 through which a tube 53 passes. The tube 53 is sealably attached to the hole in the back 15 of the housing 3 and the end of the tube 53 inside the housing 3 is connected to the second end of the evacuating pipe 43. A non return valve 51 is fitted within the tube 53 which prevents air surrounding the housing 3 entering the interior of the housing 3, when the inside of the housing 3 is under low pressure. The valve 51 could be within the evacuating pipe 43. The evacuating pipe 43 passes under tension around part of the perimeter of the rotor cage 21 as shown in figures 3 and

7 so that the pipe 43 is tight against the rollers 37. The tension in the pipe 43 can be varied in many ways such as altering the radial displacement of the wrt with respect to rollers 37 the axis of the rotor cage 21, or by changing the position of the rotor cage 21 within the housing 3 such as by drawing it closer to the back 15 of the housing 3. The tension may need altering for many reasons such as varying temperature or reduced power of a drive motor turning the rotor cage 21.

Rotation of the rotor cage 21 causes evacuation of the inside of the housing 3. Because of the presence of the tube 49 in one end of the evacuating pipe 43, the lay flat tubing of the evacuation pipe 43 is not flat at the point at which the rotating rotor cage 21 causes a roller 37 to initiate contact with the evacuation pipe 43. As the rotor cage 21 continues to rotate, the air inside the evacuation pipe 43 just in front of the roller 37 gets trapped by the roller 37 as the lay flat tubing becomes squashed by the roller 37 against the inside face 53 of the housing front wall 5. This causes pockets of air to be formed between neighbouring rollers 37. The trapped pockets of air are then pushed along the pipe 43 towards the non return valve 51 through which they pass out of the housing 3. As pockets of air get "pumped" out of the housing 3, the pressure inside the housing 3 drops. This in turn causes the pockets of air inbetween the rollers 37 to swell, causing the rollers 37 to encapsulate more volume of air on each pass. Air in the evacuating pipe 43 near the perforated tube 49 is maintained because the perforations permit the air in the housing 3 to pass into the pipe 43. The increased swelling of the evacuation pipe 43 causes the pump to become more efficient at low pressure.

The above described vacuum pump therefore operates on a peristaltic principle, by squeezing pockets of air along the pipe 43 .

Referring to figures 4-7, the filtering pipe 45 is a composite pipe comprising a first or internal lay flat pipe 57, made from a filtering material, tapering from a large input end 59 to a smaller end output end 61, and a second or external lay flat pipe 63 made from an impermeable material enveloping the first lay flat pipe 57 and preferably (although not necessarily) having a small end at the input end 59 and a larger end at the output end 61. The filtering pipe 45 is fitted around the rotor cage 21 in the same way as the evacuation page 43 and extends through the back 15 of the housing 3 as shown at 63, 65 in similar manner to the evacuating pipe 43. The output end 61 comprises three tubes 67 & 71, connected to an output terminal plate 72 and the input end 59 comprises one tube 69 connected to an input terminal plate 70. The terminal plates 70 and 72 optionally contain viewing ports to permit the condition of the mixture to be seen either prior to, during or post filtering. The apparatus can then be made to run either faster or slower depending upon what was seen. All the tubes 67, 69 & 71 of the filtering pipe 45 extend through the back 15 of the housing and thus communicate with the exterior of the housing, but each of the tubes 67 and 71 is fitted with a non return valve 73. Thus mixtures requiring filtering can be fed into the filtering pipe 45 at the input end 59 and pass out of the filtering pipe 45 at the output end 61.

The rotation of the rotor cage 21 causes the mixture to be filtered to be pushed along the filtering pipe 45 in the same manner as the air in the evacuating pipe 43. The mixture is preferably aerated so that the mixture which is usually a non expandable substance, will expand in the pipe 45, as it enters the filtering pipe 45, due to entering the pipe 45 at a larger pressure than the inside of the housing 3. As the mixture is forced along the filtering pipe 45 by the rollers 37, the air in the mixture expands through the filter material of the inner lay flat pipe 57 into the outer part of the filtering pipe 45. The expansion draws the finer material out of the mixture through the filtering material 57. Because the size of the outer pipe 63 of the filtering pipe 45 gets continually bigger towards the output end 61 of the pipe 45, the expansion continues throughout the length of the filtering pipe 45. Conversely, the inner pipe 57 contracts towards the output end 61, thus squeezing the mixture, and forcing the finer material out of the mixture, through the filter material 57, and into the outer part of the pipe 45 . The fine part of the filtered mixture leaves the housing 3 via the two exit tubes 67, whereas the coarser part of the mixture leaves the housing 3 via the single exit tube 71.

The mixture to be filtered is pumped through the filtering pipe 45, and hence filtered, by forcing pockets of mixture along the pipe from the input end 59 to the output end 61 using a peristaltic principle.

Tests have proved that a partial vacuum of the order 7 to 10 inches (178 to 254 mm) of Mercury is effective for the efficient pumping operation of combined liquid/solids flow streams. The reference herein to a vacuum is intended to refer to a "negative" pressure, or partial vacuum of this order (or greater) and not to a "total" vacuum.

The speed of rotation of the rotor cage 21 controls the pumping speed of the pumping unit 1.

For accelerated vacuum build up, more than one evacuating pipe 43 can be incorporated.

To use the pumping unit 1 for pumping a fluid without filtering the fluid, a filtering pipe 45 with the filtering lay flat pipe 57 removed from inside the impermeable pipe 63 could be used.

With wider pumping units 1, more than one filtering pipe 45 can be incorporated into the unit.

An advantageous feature of the invention is that none of the pipes require manual priming in order to start pumping since they are self priming.

The sizes of the pipes 43 & 45 are chosen to cope suitably with the material requiring pumping. High viscosity fluids would require a larger size filtering pipe than a less viscous fluid. Similarly, the filtering material is chosen to allow the filter to let only the required materials to pass through it. The space between the rollers and the internal surface of the semi-cylindrical face of the housing can also be varied depending on the materials to be pumped through and filtered by the pipes.

A further development of the filtering pipe 45 incorporates very small rubber pipes on the outer side of the filtering material 57, running the length of the filtering pipe 45. These small pipes are made of a very soft rubber, such as A.S.T.M. (NR) with an intercellular linked formation which compresses rapidly when the rollers 37 pass over the filtering pipe 45. The rubber pipes prevent the inner pipe 57 from sticking to the outer pipe 63 whilst compressed.

To prevent the inner surface of the housing 3 from damaging the lay-flat tubing 43 and 45 during compression by the rollers 37, the inner surface of the housing 3 (and/or the outer surface of the rollers 37) can be coated with a nonabrasive material.

The action of the mixture being forced through the pipe acts as a self cleaning mechanism and only occasional thorough cleaning of the filter is necessary. This can be undertaken by "backwashing" .

The rollers can act as πanglers breaking up the solid parts of a mixture. To this end the pumping unit can be adapted not only to filter and pump materials, but also to smooth a fluid. Crushing Pressures in excess of 80 psi are obtainable.

The inner face of the housing 3 is optionally lined with a layer of material which has cellular linkage formations.

An alternative embodiment is shown in figures 8 & 9 in which the pumping unit 80 comprises a substantially cylindrical housing 82, a rotor cage 84 with four rollers 37, spacer bars 27, an evacuating pipe (not shown) , and a filtering pipe (not shown) .

The pumping process is achieved in a similar manner as with the preferred embodiment, but whereas previously the rollers forced the mixture and air to the output ends of the pipes by squeezing the lay flat pipes against the inner surface 55 of the semi-cylindrical front 5, the alternative embodiment forms the pockets of air and mixture by squeezing the pipes against the rollers 37 under the tension of the pipes around the rotor cage 84. In this manner, there is room inside the housing to attach the mounting points for the pipes to the housing wall at any point of the inside of the housing 82.

It is envisaged that the pumping unit will be mounted to the floor. However, mobile units, such as mounted on the back of a tanker, and portable units, such as small units for domestic use, are considered to be possible.

By using lat flat tubing (or piping) in the apparatus described above, in combination with a vacuum (reduced pressure) within the housing, considerable cost savings can be made. Such tubing is similar to hoses used by fire brigade and is very much less expensive than normal resiliently deformable circular tubing traditional used in peristaltic pumps. Furthermore, under the described vacuum conditions, such tubing will rapidly regain its "circular" shape, thus speeding up the pumping/separating operation and hence the throughput of the apparatus.

The filtering process is generally to sparate liquids from solids. However, by using an appropriate filter, material containing liquids of different viscosities could be separated. One such use is cleaning oil from water after an oil spill.

Further considered uses are separating the oil from drilling mud during oil drilling, or separating water from soil at a dewatering sight of a civil engineering project on a marsh.

It will of course be understood that the present invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the invention.

Claims

CLAIMS :

1. A method of separating solids from liquids in a mixture of liquids and solids, comprising the steps of pumping the mixture through a composite tube having an internal tube portion formed of filtering material, and surrounding the internal tube portion, an external tube portion of impervious material, wherein the mixture is fed to an inlet end of the internal portion, which is of larger cross sectional area than an outlet end thereof, thus causing liquid to be forced through the filtering material, and into the space between the internal and external tube portions, and causing the said liquid to pass through at least one liquid outlet from said space, and causing the solids to be forced through the outlet of the internal tube portion.

2. A method according to Claim l wherein the mixture is pumped through the composite tube by entraining the composite tube, around a rotary cage having rollers on its surface, and causing the cage to rotate so that it forces pockets of the mixture along the tube from its inlet and to its outlet end, using peristaltic principles.

3. A method according to Claim 2 wherein the tube is under tension.

4. Apparatus for separating solids from liquids in a mixture of solids and liquid, comprising a composite tube having an internal tube portion formed of filtering material and an external tube portion, surrounding the internal tube portion, and made of an impervious material, wherein the internal tube portion has an inlet end of larger cross sectional area than an outlet end thereof, and pump means for forcing the mixture through the composite tube, whereby solids are pumped from the inlet end of the internal tube portion and cut of the outlet end, whereas liquids are forced through the filtering material and out of an outlet of the external tube portion.

5. Apparatus according to Claim 4 wherein the external tube portion tapers and is of the same cross sectional area as the internal tube portion at its inlet end, but at the outlet end thereof, is of greater cross sectional area, e.g. diameter, and communicates with at least one liquid outlet.

6. Apparatus according to Claim 5 wherein the internal and external tube portions are made up of circular lay flat tubing.

7. Apparatus according to Claim 4, 5 or 6 wherein the external tube portion is connected at one end thereof to the inlet end of the internal tube portion and at the opposite thereof to the outlet end of the internal tube portion, with its outlet being located adjacent this end of the tube portion.

8. Apparatus according to Claim 7 wherein the external tube portion has a larger cross sectional area at its end connected to the outlet end of the internal tube portion.

9. Apparatus according to any one of Claims 4-8 wherein at the outlet end of the internal tube portion, a plate is provided having a central aperture therein to which the outlet end of the internal tube portion is connected, and the outlet end of the external tube portion is also connected to the plate, there being at least two outlets for the external tube portion also provided in the plate.

10. Apparatus according to any one of claims 4-9 and further including a rotary cage having rollers on its periphery, the axes of which are parallel to the rotary axis of and circumferentially spaced around the periphery of the rotary cage, and the composite tube is entrained under tension with its inlet and outlet ends held stationary, around part of the periphery of the cage, so that when the cage is rotated, mixture located in the composite tube will be forced through the tube using peristaltic principles.

11. Apparatus according to Claim 11 wherein the cage and composite tube are located in a housing having an arcuate wall portion and two end walls in which end walls the cage is journalled for rotation about said axis, but of slightly smaller radius than that of the arcuate wall portion, and the composite tube is sandwiched between the rotating cage and arcuate wall portion.

12. Apparatus according to Claim 11 wherein the arcuate wall portion is part cylindrical and concentric with the said rotary axis.

13. A peristaltic pump comprising a rotary cage having rollers on a surface thereof, and a fluid tight housing having an arcuate wall and a lay flat tube entrained over at least some of the rollers of the cage, so as to extend between the said rollers and the arcuate wall of the housing, one end of the lay flat tube being connected to an outlet in a wall of the housing, and an opposite end thereof being connected to an inlet in a wall of the housing, there being a non return valve in the outlet to prevent fluid from entering the housing, and wherein means is provided to reduce the pressure within the housing to cause the lay flat tube to expand from its lay flat state into a tubular state.

14. A pump according to Claim 13 wherein the arcuate wall is part cylindrical and concentric with a rotational axis of the cage, but having a marginally larger radius than that of the arc subtended by the rollers when the cage is rotated.

15. A pump according to Claim 13 or 14 wherein spacing of the rollers from the arcuate wall is adjustable

16. A pump according to Claim 13, 14 or 15 wherein the means to reduce the pressure is a peristaltic vacuum pump.

17. A pump according to any one of Claims 13-16 wherein the radius of the internal periphery of the arcuate wall of the housing is only marginally larger than the radius of an arc subtended by a surface of the rollers when the cage is rotated so that there is just sufficient room for the lay- flat tubing to be located between the two arcuate surfaces.

18. A pump according to any one of Claims 13-17 wherein the lay-flat tubing is entrained around the cage under tension.

19. A pump according to any one of Claims 13-18 wherein the rollers are supported for rotation about their longitudinal axes between parallel spaced end walls of the housing.

20. A pump according to any one of Claims 13-19 wherein the spacing of the rotational axes of the rollers from the rotational axis of the cage is adjustable.

21. A method of pumping peristaltically, comprising the steps of: locating a lay-flat tube within a housing, connecting one end of the tube to an inlet in a wall of the housing and connecting an opposite end of the tube to an outlet in the wall of the housing, and locating a central region of the lay-flat tube so that it extends around a part of cage rotatable in the housing and between rollers supported on the periphery of the cage and an arcuate wall of the housing which wall is concentric with the rotational axis of the cage, and causing said cage to rotate whereby fluid within the lay-flat tube is forced along the tube from the inlet to the outlet as the rollers rotate around the rotational axis of the cage, and subjecting the interior of the housing to a pressure which is less than that surrounding the housing to cause the lay-flat tube to be inflated with the fluid to be pumped.

22. A nethod according to Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

23. Apparatus for separating solids from liquids in a mixture of solids and liquids, substantially as hereinbefore described with reference to the accompanying drawings.

24. A method according to Claim 21 and substantially as hereinbefore described with reference to the accompanying drawings.

25. A peristaltic pump, substantially as hereinbefore described with reference to the accompanying drawings.

26. An apparatus for creating a pressure within a closed housing which is less than the external pressure surrounding the housing, using peristaltic pumping principles, said apparatus comprising a closed housing having a side wall at least part of which is arcuate, and a pair of spaced opposed end walls connected by said part arcuate side wall, a cage rotatable within the housing, the cage having rollers spaced around its periphery and a lay-flat tube extending around the cage and located between the peripheries of the rollers and the internal surface of the arcuate side wall, one end of the lay-flat tube being connected to an outlet in a wall of the housing and the opposite end of the lay-flat tube being connected to a perforated rigid member fixedly secured within the housing, and means to cause rotation of the cage such that air within the housing will be drawn through the perforations in the rigid member and pumped along the tube in peristaltic manner from the perforated member and through the outlet, there being a non-return valve located in the tube or outlet to prevent air from re-entering the tube, whereby the pressure within the housing is reduced relative to that around the housing.

27. Apparatus according to Claim 26 wherein the arcuate side wall is part cylindrical.

23. A method of reducing the pressure of a fluid within a closed housing, comprising the steps of: forming the housing with a part arcuate side wall, causing a rotor within the housing to be rotated so that rollers located at its periphery define a cylindrical arc spaced from but generally parallel to the internal surface of the part arcuate side wall, entraining a lay-flat tube around the cage over the rollers so that the tube is located between the rollers and the part arcuate side wall, securing an outlet end of the tube to an outlet in a wall of the closed housing, providing a non-return valve in the outlet or the tube, securing an opposite end of the tube to a rigid perforated member fixedly secured within the housing, and causing the cage to rotate so that fluid from within the interior of the housing and passing into the interior of the lay-flat tube through the perforated member is pumped in peristaltic manner through the tube and out of the outlet, thereby reducing the pressure of the fluid within the housing relative to that surrounding the housing.

29. A method according to Claim 28 wherein, the arcuate part of the side wall of the housing is formed as part of a cylinder and is closely spaced from and parallel to the arc defined by the rotating rollers.

30. A method according to Claim 28 wherein the side wall of the housing is formed as a cylinder and wherein the lay-flat tube is entrained under tension over the rollers on the cage.

31. A peristaltic pump as claimed in Claim 16 wherein the peristaltic vacuum pump is the apparatus claimed in Claims 26 or 27, and wherein the housings and cages are a common housing and cage, around the latter of which two lay flat tubes are entrained.

32. A method of reducing the pressure of a fluid within a closed housing, substantially as hereinbefore described with reference to the accompanying drawings.

33. Apparatus for creating a pressure within a closed housing which is less than the external pressure surrounding the housing, substantially as hereinbefore described with reference to the accompanying drawings.