Filter

Abstract

A filter unit for filtering particulates and other foreign matter from a fluid supply, comprising a filtering chamber. At least a portion of an exterior of the filtering chamber being provided with a mesh through which fluid may enter the filtering chamber in use. The mesh being sized to filter particulates and other foreign matter from the fluid. The filter unit further comprising an outlet through which filtered fluid exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh. The axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh. The filter unit further comprising a dedicated pump having an inlet communicating with the filtering chamber and an outlet communicating solely with the rotatable member such that operation of the pump causes filtered fluid from within the filtering chamber to be pumped through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

Description

[0001] The present invention relates to a filter unit for filtering particulates and other foreign matter from a fluid supplies. In addition, the invention relates to filter unit assemblies and filtration systems and methods of filtration using the filter unit.

[0002] It is known to provide filter units and filtration systems in water supplies in order to remove particulate matter and other foreign matter from the water supply. One example of the use of such a filter unit and filtration system is in filtering the water supply for a fish pond or aquarium.

[0003] It is known to filter a water supply by passing the water supply through a small aperture mesh to thereby remove particles and foreign matter having a diameter greater than the aperture size of the mesh. However, a problem with such a system is that the mesh quickly becomes blocked with the particles and foreign matter removed from the water supply at which point the filtration system ceases to function and the water supply is substantially cut-off. It is therefore necessary to regularly clean the meshes of such filtration systems. This process normally involves dismantling the filtration system which is both time-consuming and complicated. In addition, during maintenance of the system, the water supply must be cut off.

[0004] GB 2 293 333 proposes one solution to such a problem wherein a filtering chamber is provided surrounded by a small aperture mesh. Water is drawn through the unit and through the mesh and out of an outlet pipe by means of a pump. A tapping of filtered water from the pumped outlet of the filter chamber is then diverted via a return conduit into a back washing nozzle assembly in the form of a rotatable impeller. The water is spread from outlets of the impeller against the interior face of the mesh in the hope of dislodging particles and debris on the exterior face of the mesh. However, the device of GB 2 293 333 suffers from a number of drawbacks. Firstly, the filter is only useable with an actively pumped filtration system. In other words, the filter unit cannot be used with a gravity-fed system which is commonly found in larger aquaria and fish ponds. Secondly, in order to produce a sufficient dislodging force of the water from the impeller, it has been found necessary to divert a very significant proportion of the filtered water from the outlet back into the rotatable impeller. Potentially up to 90% of the water pumped through the filter unit must be diverted back to the rotatable impeller. Even then, the minimum pore size of the mesh which may be used with such a filter is restricted to greater than about 250 microns otherwise the pressure drop across the filter unit becomes too great and the volumetric throughput of the filter unit becomes too low.

[0005] The present invention aims to provide a filter unit which overcomes the disadvantages of known devices.

[0006] Accordingly, the present invention provides a filter unit for filtering particulates and other foreign matter from a fluid supply, comprising a filtering chamber, at least a portion of an exterior of the filtering chamber being provided with a mesh through which fluid may enter the filtering chamber in use, the mesh being sized to filter particulates and other foreign matter from the fluid, the filter unit further comprising an outlet through which filtered fluid exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh, the axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh, the filter unit further comprising a dedicated pump having an inlet communicating with the filtering chamber and an outlet communicating solely with the rotatable member such that operation of the pump causes filtered fluid from within the filtering chamber to be pumped through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

[0007] The present invention also provides a filter unit assembly comprising a filter unit as provided above and a tank housing in which the filter unit is located, the tank housing being provided with an inlet for entry of fluid into the tank unit and the outlet of the filter unit forming the outlet of the tank housing.

[0008] The present invention further provides a filtration system comprising one or more filter units assemblies as provided above.

[0009] The present invention further provides a method of filtering fluid to remove particulates and other foreign matter comprising the steps of passing the fluid through a filtering chamber having a mesh sized to filter the particulates and other foreign matter from the fluid, outputting the fluid from the filtering chamber through an outlet of the filtering chamber, wherein a dedicated pump is used to pump fluid from the filtering chamber exclusively through a rotatable member located within the filtering chamber to exit through at least one outlet of the rotatable member to impinge on an interior face of the mesh so as to dislodge particulates and other foreign matter located on an exterior face of the mesh.

[0010] The present invention further provides a filtration system for filtering particulates and other foreign matter from a fluid supply, comprising a tank with an inlet and an outlet, a filtration unit through which fluid must pass to reach the outlet, and a sump in which particulates and other foreign matter from the fluid accumulates, the sump having an outlet, a drainage conduit communicating with the outlet, a pump for withdrawing fluid and accumulated particulates and other foreign matter through the outlet and discharging it to a drainage conduit, and a programmable controller for operating a valve and pump.

[0011] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0012] FIG. 1 is a side elevation of a filter unit in accordance with the present invention;

[0013] FIG. 2 is a further side elevation of the filter unit of FIG. 1 with certain parts omitted for clarity;

[0014] FIG. 3 is a cross-sectional elevation of the filter unit of FIG. 1, again with certain parts omitted for clarity;

[0015] FIG. 3a is a cross-sectional elevation of an alternative filter unit, again with certain parts omitted for clarity;

[0016] FIG. 3b is a plan view of the filter unit of FIG. 3a;

[0017] FIG. 4 is a top plan view of the filter unit of FIG. 1, showing hidden components in broken lines;

[0018] FIG. 5 is a cross-sectional detail of part of the filter unit of FIG. 3;

[0019] FIG. 6 is a cross-sectional detail of another part of the filter unit of FIG. 3;

[0020] FIG. 6b is a cross-sectional detail of an alternative part to that of FIG. 6;

[0021] FIG. 7 is a cross-section detail of a further part of the filter unit of FIG. 3;

[0022] FIG. 8 is a side elevation of a rotor as used in the filter unit of FIG. 1;

[0023] FIG. 9 is a top plan view of the rotor of FIG. 8;

[0024] FIG. 9a is a top plan view of an alternative rotor;

[0025] FIG. 10 is a perspective view of a detail of the rotor of FIG. 8;

[0026] FIG. 11 is a top plan view of an inlet conduit as used in the filter unit of FIG. 1;

[0027] FIG. 12 is a cross-sectional side elevation of the inlet conduit of FIG. 11;

[0028] FIG. 13 is a schematic elevation of the filter unit of FIG. 1 in a first type of tank housing;

[0029] FIG. 13a is a schematic elevation of another filter unit assembly in accordance with the present invention;

[0030] FIG. 13b is a schematic elevation of another filter unit assembly in accordance with the present invention;

[0031] FIG. 14 is a schematic elevation of the filter unit of FIG. 1 in a second type of tank housing;

[0032] FIG. 15 is a schematic elevation of the filter unit of FIG. 1 in a third type of tank housing connected to a biological cleaning stage housing;

[0033] FIG. 16 is a schematic elevation of a plurality of the filter units of FIG. 1 in a vertical stack formation; and

[0034] FIG. 17 is a schematic elevation of an alternative tank housing in accordance with the present invention;

[0035] FIG. 17a is a schematic elevation of an alternative tank housing in accordance with the present invention;

[0036] FIG. 17b is a schematic elevation of another alternative tank housing in accordance with the present invention; and

[0037] FIG. 18 is a cross sectional view of another filtration unit in accordance with the present invention; and

[0038] FIG. 19 is a schematic view of a filtration system in accordance with the present invention.

[0039] Referring to FIGS. 1 to 3, a filter unit 1 in accordance with the present invention comprises a filter unit housing 10 having circular upper and lower covers 11, 12. A mesh 13 extends around the circumference of the filter unit housing 10 extending between the upper cover 11 and lower cover 12. The upper cover 11, lower cover 12 and mesh 13 together define a cylindrically shaped filter chamber 9.

[0040] Preferably the materials of the filter unit, except where otherwise mentioned, are made of stainless steel grade 316.

[0041] An outlet 15 is provided at a centre of the filter chamber 9 in the lower cover 12. A rubber sleeve 16 located at an end of the outlet 15 allows the outlet of the filter chamber 9 to be connected to a pipe or other conduit of varying diameter from approximately 7.5 cm to 15 cm.

[0042] Referring to FIGS. 3 to 7, the mesh 13 is mounted to the upper cover 11 and lower cover 12 by means of tie brackets 33. Each tie bracket 33 comprises an elongated strip of metal having an inturned flange at either end. The mesh 13 is spot welded to a number of tie brackets 33. The mesh and tie bracket assembly is then connected to the upper cover 11 and the lower cover 12 by virtue of bolts 28, 26. A ‘fluidtight’ seal is provided by annular seals 20, 27 provided in annular channels 34, 35 formed in the upper cover 11 and lower cover 12 respectively. As seen in FIGS. 5 to 7, the mesh 13 protrudes into the upper and lower seals 27, 20 to form an improved connection. As a result fluid can only enter the filter chamber 9 through the mesh 13.

[0043] An alternative seal is illustrated in FIG. 6b wherein the annular channel is dispensed with. Instead an enlarged gasket or o-ring 20′ is provided which is sandwiched between the tie bracket 33 and lower cover 12 as the bolt 26 is fastened. As a result the O-ring 20 bulges outwards to form a face seal against the mesh 13. This seal may be used on the upper and lower covers 11, 12.

[0044] The mesh 13 is also made of stainless steel grade 316. The aperture size of the mesh 13 can be varied depending on the required degree of filtration. However, in accordance with the present invention aperture sizes of 200 microns or less can be utilised. One form of mesh 13 is a Hollander weave mesh of aperture size 100 microns. The Hollander weave construction has been found to offer good resistance to work hardening and fatigue failure. Other mesh types such as wedge wire screen (also known as triangular bar screen) and plain weaves may be used. The mesh 13 may also be made of nylon of a suitable thickness.

[0045] A rotatable member in the form of a rotor 14 is provided within the filter chamber 9 having an axis of rotation which is substantially vertical and coincident with the major axis of the cylindrical filter chamber 9. The rotor 14 is mounted to the upper cover 11 and lower cover 12 by bolts.

[0046] Referring to FIGS. 8 to 10, the rotor 14 of the filter unit 1 comprises a vertically orientated hollow rotor shaft 21 and a hollow rotor arm 22 which extends substantially perpendicular thereto. Preferably, the rotor arm 22 and rotor shaft 21 are welded together. At each distal end of the rotor arm 22, there is provided a rotor nozzle 23. Each rotor nozzle 23 comprises an outlet 29 which is angled at an angle a (alpha) to a radial direction 36 passing coincident to the rotor arm 22 as shown in FIG. 9. Angle a may be varied substantially 0 and 90 degrees. Preferably, a is between 35 and 50 degrees. In one example the two outlets 29 are both set with an &agr; of 45 degrees. The two outlets 29 may be set at different angles; for example, one outlet may have an &agr; of 35 degrees and the other 50 degrees. Alternatively, one of the outlets may be at 0 degrees and the other outlet at an angle greater than 0 degrees.

[0047] Alternatively, as shown in FIG. 9a, the nozzle outlets 29 may be set at 0 degrees and one or more openings 29a provided in the side walls of the nozzle 23 through which a proportion of the water passes in order to rotate the rotor 14.

[0048] A pump 17 is provided attached to an exterior of the filter unit housing 10. An inlet of the pump 17 is connected to an interior of the filter chamber 9 by means of an aperture 32 in the lower cover 12 (as shown in FIG. 4). An outlet of the pump 17 connects solely to the rotor 14 via an aperture 31 in the lower cover 12 and an inlet conduit 19. The pump 17 is consequently dedicated to supplying water to rotor 14.

[0049] The pump 17 is preferably an electric pump powered by an external power source. The pump has a rating of greater than 2,000 litres per hour and preferably greater than 4,000 litres per hour. One example of a suitable pump is the ‘Nautilus 6,000’ pump manufactured by Oase having a rating of 6,000 litres per hour.

[0050] Referring to FIGS. 11 and 12, the inlet conduit 19 of the filter unit 1 is provided with a first aperture 31a and a second aperture 30a. When positioned in the filter unit 1, the first aperture 31a coincides with the aperture 31 in the lower cover which provides a connection with the outlet of the pump 17. Likewise, the second aperture 30a is coincident with a base of the hollow rotor shaft 21. As such, the outlet of the pump 17 communicates with the interior of the rotor 14 via the pump outlet aperture 31, aperture 31a, internal conduit 19, aperture 30a and rotor shaft 21.

[0051] An air bleed valve 18 is provided in upper cover 11 to allow air trapped in the filter unit 1 during installation to be bled off.

[0052] The use of the filter unit 1 will now be described by way of example only and for clarity for use with water. However, other fluids, being liquids or gases, may be filtered using the present invention.

[0053] The filter unit 1 is installed in use in a tank housing 40 to form a filter unit assembly. FIG. 13 shows a first type of tank housing 40 which comprises an inlet 41 located at or near a top of the tank housing 40, an outlet pipe 42 and a sump 43 provided with a bottom drain line 44. The filter unit 1 is installed in the tank housing 40 with the outlet 15 being connected to the outlet pipe 42 by means of the rubber sleeve 16 and a jubilee clip. The tank housing 40 is then filled with water from inlet 41. During this stage the bleed valve 18 may be operated to remove any air trapped in the filter unit 1.

[0054] In operation, there is a flow of water from the inlet 41 to the outlet pump 42 such that the filter unit 1 is surrounded by water to be filtered. Advantageously, locating the inlet 41 at or near the top of the tank housing 40 causes an overall movement of water downwardly through the tank housing 40 towards filter unit 1 which aids removal of particulates and other foreign matter from the mesh 13 and speeds up settling of the debris in sump 43. In addition, the conical shape of the sump 43 aids downward movement of the debris towards the bottom drain line 44.

[0055] The filter unit assembly may be either gravity-fed or an actively pumped filtration assembly. Either due to the force of gravity or due to the action of the active pumping, water is passed through the tank housing 40 and filter unit 1 by entering through mesh 13 and exiting through outlet 15 into the outlet pipe 42.

[0056] At the same time, pump 17 is operated to pump water solely through rotor 14. The water pumped by pump 17 originates from within the filter chamber 9 and is therefore free of any particulates or other foreign matter larger than the aperture size of the mesh 13. Water is pumped into the pump 17 via the inlet aperture 32 in the lower cover 12 and pumped out of the pump outlet aperture 31 only into the inlet conduit 19 and rotor shaft 21. The pumped water is then forced along both arms of the rotor arm 22 and out of the rotor outlets 29 of rotor nozzles 23. Due to the angle a of the outlets 29 of the rotor nozzles 23, the outflowing water causes the rotor arm 22 to rotate. The water outflowing from the rotor outlets 29 is directed against an interior face of the mesh 13 before passing therethrough. This flow of water causes particulates and other foreign matter lodged on the outer exterior face of the mesh 13 to be dislodged and to fall away from the mesh 13 into sump 43. Periodically the bottom drain line 44 is opened to remove the collected waste material.

[0057] Advantageously, since the flow of water through the rotor 14 is not taken from the outlet 42, operation of the rotor 14 does not produce a decrease in the volumetric flow rate or efficiency of the filter unit 1.

[0058] A modified type of tank housing 540 is shown in FIG. 13a in which a plate, insert or partition 511 is located. The filter unit 1 is positioned such that its mid-point is level with the partition 511. An orifice 512 is provided in the partition 511 in which the filter unit 1 is located. The partition 511 promotes downward flow within the tank housing 540 due, in part, to the pressure gradient across the partition due to a venturi effect. The downward flow helps the settling of solids in the sump of the tank housing 540 and also helps prevent the water below the partition 511 being disturbed by the water entering the tank housing through the inlet. Further, the partition 511 ensures that the water entering the tank is directed towards the mesh 13 of the filter unit 1 for filtration.

[0059] For maximum efficiency, the radius of the orifice 512 has been found to be as follows:

R0={square root}{square root over ( )}((&pgr;r2+3&eegr;)/&pgr;)

[0060] where

[0061] R0=radius of orifice

[0062] r=radius of filter in centimetres and

[0063] &eegr;=flow rate through filter in litres.

[0064] This formula can also be used to determine the radius of the tank housing in the version shown in FIG. 13, for example.

[0065] Another variant of the tank housing is shown in FIG. 13b. In this variant the function of the partition 511 has been incorporated as part of the internal shape of the housing itself. An upper region 515 of the housing is frusto-conical in shape. A lower region 516 is cylindrical in shape. The junction between the upper region 515 and the lower region 516 is located level with the mid-point of the filter unit 1. This has the same effect as in the previously described variant of creating a pressure gradient which encourages downward flow of water within the tank housing.

[0066] In addition, the tank housing comprises a sump 517 which has a much reduced cross-sectional area. This has the result of reducing the amount of water which must be emptied fro the tank housing when clearing the sump 517. In addition, the water exiting the sump 517 into drain line 518 will speed up due to the restriction in diameter. The high velocities produced ensure that all the collected debris is efficiently removed whilst only using a small volume of water.

[0067] FIG. 14 show a second type of tank housing 40′ in which the filter unit 1 may be installed. This type of installation occurs typically where an already fitted ‘vortex’ type filter unit is converted to operate with the filter unit 1 of the present invention. The installation shows how the filter unit 1 may be orientated upside-down without impairing performance. The inlet 41′ is also provided with a 90 degree elbow pipe 50 to move the effective inlet 51 of the tank housing 40′ to at or near the top of the housing. It has been found that increased performance of the filter unit 1 occurs where the tank housing 40′ is filled in a non-vortex producing manner such that the inflowing water fills the tank housing 40′ from the bottom up without a significant water flow in the radial or tangential directions. However, the filter unit 1 may be used in a vortex tank housing.

[0068] FIG. 15 illustrates a third type of tank housing 40″ in which the filter unit 1 of the present invention may be installed. The outlet 42″ of the tank housing 40″ is provided with a secondary pump 54 separate from the dedicated pump 17 of the filter unit 1. The secondary pump 54 operates to drive water through the tank housing 40″. The figure also illustrates how biological filtering or cleaning stages 55 my be arranged in series with the filter unit assembly of the present invention to form an integrated filtration system.

[0069] FIG. 16 illustrates a further embodiment of the present invention wherein a plurality of the filter unit assemblies are arranged in a vertical stack formation. The outlet 15 of the uppermost filter unit 1 is connected to the inlet 41 of the next lowermost tank housing 40 and so on down to the lowermost filter unit 1 whose outlet 15 is connected to the outlet of the filtration system. Preferably the aperture size of the meshes 13 in the filter units 1 decreases down the stack from a mesh size of 100 microns or greater in the uppermost filter unit to a mesh size of 25 microns or less in the lowermost filter unit. In this way a progressive filtration system is provided.

[0070] Adjacent filter unit assemblies may advantageously be joined sealingly with one another with the provision of gaskets or O-ring seals 60. Of course the successive filter unit assemblies may be arranged otherwise than in a vertical formation; for example, they may be arranged horizontally where the filtration system is actively pumped.

[0071] FIG. 17 shows a further embodiment of filter unit assembly in accordance with the present invention. The filter unit assembly 110 comprises a tank 112. The tank has an inlet 114 and an outlet 118. A filter unit 1 is located in the tank. Water entering the tank must pass through the filtration unit in order to leave the tank 112 through the outlet 118. A lower portion of the tank forms a sump 120 which tapers towards an outlet 122 and a drainage pipe 124.

[0072] The filter unit 1 may be as described in any of the above embodiments. Alternatively, another type of filter unit may be used in tank 112.

[0073] A drainage pipe 124 is connected to the outlet 122 of the sump 120 and is arranged with an outlet or vent to atmosphere 140 at a level higher than the level of the inlet 114 into the tank 112. This ensures that the head of water in the drainage pipe 124 is greater than that in the tank 112. Thus, water entering the tank 112 does not simply drain away, cutting off supply to the outlet 118.

[0074] However, the outlet 122 from the sump 120 to the drainage pipe 124 may also be closed by a valve 134 of any suitable type such as a gate valve or ball valve.

[0075] A pump 136 is provided to pump water and accumulated debris whenever desired (and when the valve 134 is open, if provided) from the sump 120 and along the drainage pipe 124 to waste. The pump may be of any suitable type which is able to operate without fouling due to the debris which may be present in the water.

[0076] The valve 134 (if present) and pump 136 are operated by a programmable controller 138 which includes a time clock and which can be preset to activate the valve and pump at desired intervals and for a desired length of time. For example, a conventional domestic central heating timer can be used.

[0077] The controller can be set to operate the valve 134 and pump 136 as often as necessary and for as long as necessary. For example, when the system is newly installed and the water to be filtered is particularly laden with particulates and other foreign matter, it may be necessary to clear the accumulated debris every two hours or so, operating the pump for, say, ten minutes each time. Once this initial filtration has occurred, ongoing filtration may require a lower frequency of perhaps twice a day.

[0078] FIG. 17a shows one variant of tank housing having a sump 120 which can be automatically emptied. The emptying of the sump 120 is controlled by the pressure of the dedicated pump 132 of the filter unit 1. The valve 134 connected to the drain line 124 is held shut by the water pressure from the pump 132 via a transfer means 146. The valve 134 can only open when the pump 132 is switched off. Opening of the valve 134 is caused by action of a spring 147 located in the valve 134. The switching of the pump 132 can be controlled by a timing means such as a segmented time switch 148.

[0079] FIG. 17b shows an alternative arrangement in which a pump 136 is connected to the drain point. The operating times of the pump 136 are controlled by a timing means such as a segmented time switch 148. The outlet of the pump 136 is connected to an upstanding U-bend pipe 149 to prevent drainback of waste water.

[0080] It will be apparent that a number of modifications may be made to this embodiment without departing from the scope of the invention. For example, a different type of filtration unit may be used. A filtration system comprising a number of tanks and filtration units through which water passes consecutively may be employed, with each tank including a sump and automated discharge system in accordance with the invention.

[0081] Variations to any of the embodiments described above may be made without departing from the scope of the present invention. For example, the filter unit 1 may be provided with a rotor 14 having only a single outlet 29 or more than two outlets 29. The pump 17 may be provided remote from the filter unit 1 rather than being attached thereto. In the case of multiple filter units 1, a single pump 17 may be used to supply water to all the rotors 14. The mesh 13 has been described as made of stainless steel. However, other materials such as heavy duty plastic may be utilised.

[0082] The rating of the dedicated pump 17 may be varied depending on the aperture size of the mesh 13. For example, it may be preferred to use a pump such as the ‘Oase USP60’.

[0083] Another variation which may be made to the filter unit assemblies of the above embodiments is the provision of a timer switch so as to enable operation of the rotor 14 and pump 17 at periodic intervals as opposed to continuous operation. This has the advantage that the apparatus uses less power. In addition, with the pump 17 switched off, the mesh 13 starts to become blocked by particles in the water. As it does so, the effective aperture size of the mesh 13 decreases leading to the filtration of smaller particles. When the pump 17 is activated the water from the rotor 14 tends to remove the solids on the mesh 13 in the form of ‘sheets’ which more readily settle out in the sump of the tank housing than do individual particles. The periodic operation of pump 17 is controlled by a switching means such as a simple timer. More advantageously the operation can be controlled by a float switch in the tank housing where the filter unit assembly is actively pumped. As the mesh 13 becomes progressively blocked, the water level in the tank housing starts to rise which eventually triggers the float switch to turn on the pump 17. Where the filter unit assembly is gravity fed, the float switch would be situated in a container downstream of the tank housing. In this case, blockage of the mesh 13 will lead to reduction in the water level in the downstream container thus activating the float switch and pump 17.

[0084] Where the filter unit assembly is pressurised, a pressure switch may be used as the switching means.

[0085] Advantageously, a switching relay may be used to coordinate operation of the pump 17 of the filter unit and the circulatory pump of the filtration system such that the general circulatory pump is switched off when the dedicated pump of the filter unit is switched on. This has the advantage that the water exiting the rotor 14 and impinging on the mesh 13 does not have to work against an inflow of water through the mesh 13.

[0086] FIG. 18 shows a further embodiment of the present invention in which the tank housing 540 is pressurised, in other words the filter unit assembly is part of a closed system which is not open to atmosphere. An air tight lid 545 is provided to seal the filter unit assembly. Alternatively, the tank housing 540 may be made as a pressurisable unit. The filter unit 1 and assembly may otherwise be as described in the above embodiments. In particular, the unit 1 may be located in an orifice formed in a partition 546, and a sump 543 is provided communicating with a drain line 544. A major advantage of a filter unit assembly which is pressurised is that it may be used in a filtration system that has no loss of head. Such a system is shown schematically in FIG. 19. The output of the filter unit assembly 540 inputs into a biological filter stage 560 which then outputs into a water source 570. Water is supplied from the water source 50 to the filter unit assembly 540 by a circulatory pump 580. Advantageously only one pump is required to circulate water round the whole system. This differs to current systems used in aquaculture where the filtration stage is non-pressurised. Consequently head is lost at the filtration stage and therefore another pump is required to move the water through the biological filter stage and back to the water source 570. Alternatively, and also disadvantageously, the filtration system has to be arranged with large vertical displacements between the stages to develop enough pressure head. The pressurised system of the present invention may all be arranged compactly at one level.

[0087] Another variation of the filter unit of the present invention is the use of a dedicated supply of fluid to the rotor 14 of the filter unit 1. In the embodiments described above, the rotor is supplied with water by means of dedicated pump 17. Alternatively a different dedicated supply may be utilised such as a mains water supply or a source of otherwise pressurised water. For example, rotor 14 could be plumbed in communication with a header tank of water having sufficient head to provide adequate water pressure.

[0088] In a further variation, the rotor 14 may be supplied with a dedicated supply of a gas such as air. Air may be used where the medium being filtered is either a gas or a liquid. The rotor gas may be from a compressed gas supply or air powered by an air pump having a rating of 100 litres/minute. The source of the gas may be from within the filter unit 1 where the medium being filtered is that gas or alternatively the source may be external.

[0089] In another variation, the motive force for rotating the rotor 14 may be provided by means other than the throughput of fluid though the rotor. For example an electric motor may be used or mechanical gears driven by the flow of fluid. In this case the nozzles 29 of the rotor do not need to be angled.

[0090] In a further variation, the filter unit 1 may be constructed as shown in FIGS. 3a and 3b wherein the top cover 11 is removeable simply by undoing a finger nut 11a threaded on spindle 21. Once the top cover 11 is removed the mesh 13 may be lifted out in one piece for cleaning and/or replacement and the rotor 14 may be accessed.

[0091] Whilst the present invention has been described above in detail for use with water it is to be understood that it applies equally to other fluids which require filtering such as blood, plasma, wine, air, nitrogen, oxygen etc. The apparatus and method of the present invention may be used in many fields, for example, in filtering in medical applications, in filtering air for dust extraction or air conditioning either of a room or in a portable device such as a cleaner. The filter may also be used to filter water for irrigation, fisheries, hatcheries, swimming pools, baths and ponds in general. For example, using a pressurised filtration system as shown in FIG. 18 the present invention has found particular application in the extraction of dust, for example MDF dust, from air. The filter unit and assemblies of the present invention find ready application in a wide range of fields. The aperture size of the mesh may be adjusted depending on the nature of the medium being filtered. For example, for the filtering of air, an aperture size down to 1 micron may be used with no difficulty.

Claims

1. A filter unit for filtering particulates and other foreign matter from a fluid supply, comprising a filtering chamber, at least a portion of an exterior of the filtering chamber being provided with a mesh through which fluid may enter the filtering chamber in use, the mesh being sized to filter particulates and other foreign matter from the fluid, the filter unit further comprising an outlet through which filtered fluid exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh, the axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh, the filter unit further comprising a dedicated pump having an inlet communicating with the filtering chamber and an outlet communicating solely with the rotatable member such that operation of the pump causes filtered fluid from within the filtering chamber to be pumped through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

2. A filter unit as claimed in claim 1, wherein the pump is located remote from the filtering chamber.

3. A filter unit as claimed in claim 1, wherein the pump is attached to the filtering chamber.

4. A filter unit as claimed in any preceding claim, wherein the pump has a rating of greater than 2,000 litres per an hour, preferably, greater than 4,000 litres per hour.

5. A filter unit as claimed in any preceding claim, wherein the rotatable member has two outlets located at opposite ends of the rotatable member.

6. A filter unit as claimed in claim 5, wherein at least one of the outlets of the rotatable member is angled at between 0° and 90° of a radial direction passing through the axis rotation of the rotatable member.

7. A filter unit as claimed in claim 6, wherein at least one of the outlets of the rotatable member is angled at between 30° and 50° of a radial direction passing through the axis rotation of the rotatable member.

8. A filter unit as claimed in any preceding claim, wherein at least one outlet of the rotatable member is angled at substantially 90° to a radial direction passing through the axis rotation of the rotatable member.

9. A filter unit as claimed in claim 7, wherein at least one of the outlets of the rotatable member is angled at substantially 45° to the radial direction.

10. A filter unit as claimed in any preceding claim wherein means are provided to rotate the rotor.

11. A filter unit as claimed in claim 10 wherein the means are an electric motor.

12. A filter unit as claimed in claim 10 wherein the means are mechanical gears driven by a flow of fluid.

13. A filter unit as claimed in any preceding claim, wherein the mesh has an aperture size of less than 1000 microns.

14. A filter unit as claimed in claim 13, wherein the mesh has an aperture size of approximately 100 microns or less.

15. A filter unit as claimed in claim 13, wherein the mesh has an aperture size of approximately 10 microns or less.

16. A filter unit as claimed in any preceding claim, wherein the mesh is one of a hollander weave mesh, a wedge wire screen or a plain weave.

17. A filter unit as claimed in any preceding claim, wherein the mesh is made of stainless steel grade 316.

18. A filter unit as claimed in any of claims 1 to 16 wherein the mesh is made of nylon.

19. A filter unit as claimed in any preceding claim, wherein the outlet of the pump communicates with a basal portion of the rotatable member via an inlet conduit.

20. A filter unit as claimed in any preceding claim, wherein the outlet of the filter unit comprises a flexible sleeve for attaching the outlet to a pipe or other conduit.

21. A filter unit as claimed in claim 20, wherein the sleeve is made of rubber or similar material.

22. A filter unit for filtering particulates and other foreign matter from a fluid supply, comprising a filtering chamber, at least a portion of an exterior of the filtering chamber being provided with a mesh through which fluid may enter the filtering chamber in use, the mesh being sized to filter particulates and other foreign matter from the fluid, the filter unit further comprising an outlet through which filtered fluid exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh, the axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh, the filter unit further comprising a dedicated supply of fluid having an outlet communicating solely with the rotatable member such that fluid is supplied through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

23. A filter unit as claimed in claim 22 wherein the dedicated supply of fluid is a source of pressurised water.

24. A filter unit as claimed in claim 23 wherein the water is pressurised by mains pressure.

25. A filter unit as claimed in claim 23 wherein the water is pressurised by an impeller.

26. A filter unit as claimed in claim 23 wherein the water is pressurised by a head of water.

27. A filter unit as claimed in claim 22 wherein the dedicated supply of fluid is a source of pressurised gas.

28. A filter unit as claimed in claim 27 wherein the gas is air.

29. A filter unit as claimed in claim 28 wherein the air is pressurised by an air pump.

30. A filter unit assembly comprising a filter unit as claimed in any preceding claim and a tank housing in which the filter unit is located, the tank housing being provided with an inlet for entry of fluid into the tank unit and the outlet of the filter unit forming the outlet of the tank housing.

31. A filter unit assembly as claimed in claim 30 wherein fluid is pumped through the tank housing by a secondary pump separate from the dedicated pump.

32. A filter unit assembly as claimed in claim 30, wherein the inlet is orientated so as to create a vortex of fluid within the tank housing to aid separation of particulates and other foreign matter.

33. A filter unit assembly as claimed in claim 32 wherein fluid is fed by gravity through the tank housing.

34. A filter unit assembly as claimed in any of claims 30 to 33, wherein the tank housing inlet is located at or near a top of the tank housing.

35. A filter unit assembly as claimed in claim 34, wherein the tank housing inlet is provided with an elbow so as to deflect fluid entering the tank housing into a direction other than the radial.

36. A filter unit assembly as claimed in any of claims 30 to 35 wherein the tank housing comprises a sump in which particulates dislodged from said filter unit accumulate.

37. A filter unit assembly as claimed in any of claims 30 to 36 wherein the filter unit is located in an orifice.

38. A filter unit assembly as claimed in claim 37 wherein the radius of the orifice is defined by:

R0={square root}{square root over ( )}((&pgr;r2+3&eegr;)/&pgr;)

where

R0=radius of orifice

r=radius of filter in centimetres and

&eegr;=flow rate through filter in litres.

39. A filter unit assembly as claimed in any of claims 37 to 38 wherein the orifice is provided in a partition forming a portion of the tank housing.

40. A filter unit assembly as claimed in any of claims 30 to 39 wherein switching means are provided for enabling periodic operation of the dedicated pump.

41. A filter unit assembly as claimed in claim 40 wherein the switching means is a timer switch.

42. A filter unit assembly as claimed in claim 40 wherein the switching means is a float switch activatable by the fluid level in the tank housing.

43. A filter unit assembly as claimed in claim 41 wherein the switching means is a float switch activatable by the fluid level in a container downstream of the tank housing.

44. A filter unit assembly as claimed in any of claims 42 to 43 wherein means are provided to inhibit entry of fluid into the tank unit when the dedicated pump is switched on.

45. A filter unit assembly as claimed in claim 44 wherein a circulatory pump of the filtration system is switched off when the dedicated pump is switched on.

46. A filter unit assembly as claimed in any of claims 30 to 45 which is pressurisable.

47. A filter unit assembly as claimed in claim 46 wherein the tank housing is a pressure vessel.

48. A filtration system comprising one or more filter units assemblies as claimed in any of claims 30 to 47.

49. A filtration system as claimed in claim 48, comprising a plurality of filter unit assemblies as claimed in any of claims 30 to 47, wherein the filter unit assemblies are arranged sequentially, wherein the tank housing outlet of each filter unit assembly is connected to the tank housing inlet of the subsequent filter unit assembly or outlet of the filtration system in the case of the last filter unit assembly.

50. A filtration system as claimed in claim 49 wherein the sequential filter unit assemblies are stacked vertically.

51. A filtration system as claimed in claim 50, wherein a gasket or O-ring seal is provided between adjacent filter unit assemblies.

52. A filtration system as claimed in any of claims 49 to 51, wherein the mesh aperture size of the filter unit in each successive filter unit assembly decreases in size.

53. A filtration system as claimed in claim 52, wherein the mesh aperture size of the first filter unit assembly is 100 microns or greater.

54. A filtration system as claimed in any of claims 49 to 53, wherein the mesh aperture size of the last filter unit assembly is 25 microns or less.

55. A method of filtering fluid to remove particulates and other foreign matter comprising the steps of passing the fluid through a filtering chamber having a mesh sized to filter the particulates and other foreign matter from the fluid, outputting the fluid from the filtering chamber through an outlet of the filtering chamber, wherein a dedicated pump is used to pump fluid from the filtering chamber exclusively through a rotatable member located within the filtering chamber to exit through at least one outlet of the rotatable member to impinge on an interior face of the mesh so as to dislodge particulates and other foreign matter located on an exterior face of the mesh.

56. A method as claimed in claim 55 wherein the dedicated pump is operated periodically.

57. A method as claimed in claim 56 wherein the dedicated pump is switched on and off by virtue of the fluid level in the tank housing.

58. A method as claimed in claim 57 wherein the dedicated pump is switched on and off by virtue of the fluid level in a container downstream of the tank housing.

59. A filtration system for filtering particulates and other foreign matter from a fluid supply, comprising a tank with an inlet and an outlet, a filtration unit through which fluid must pass to reach the outlet, and a sump in which particulates and other foreign matter from the fluid accumulates, the sump having an outlet, a drainage conduit communicating with the outlet, a pump for withdrawing fluid and accumulated particulates and other foreign matter through the outlet and discharging it to a drainage conduit, and a programmable controller for operating a valve and pump.

60. A filtration system as claimed in claim 59, wherein the outlet from the sump is provided with a valve.

61. A filtration system as claimed in claim 60, wherein the valve is a gate valve.

62. A filtration system as claimed in claim 60, wherein the valve is a ball valve.

63. A filtration system as claimed in any of claims 59 to 62, wherein the controller includes a timer of the type used in central heating systems.

64. A filtration system as claimed in any of claims 59 to 63, wherein the drainage channel has an outlet or vent to atmosphere at a higher level than the inlet of the tank.

65. A filtration system as claimed in any of claims 59 to 64, wherein the filtration unit comprises a filtering chamber, at least a portion of an exterior of the filtering chamber being provided with a mesh through which fluid may enter the filtering chamber in use, the mesh being sized to filter particulates and other foreign matter from the fluid, the filter unit further comprising an outlet through which filtered fluid exits the filter unit, and a rotatable member located within the filtering chamber, the rotatable member having at least one outlet spaced from an internal face of a mesh, the axis of rotation of the rotatable member being such that the at least one outlet traverses at least a substantial portion of the internal face of a mesh, the filter unit further comprising a dedicated pump having an inlet communicating with the filtering chamber and an outlet communicating solely with the rotatable member such that operation of the pump causes filtered fluid from within the filtering chamber to be pumped through the rotatable member to exit the at least one outlet and impinge on the internal face of the mesh so as to cause particulates and other foreign matter located on an external face of the mesh to be dislodged.

66. A filter unit as claimed in any of claims 1 to 29 wherein the fluid is a liquid.

67. A filter unit as claimed in claim 66 wherein the liquid is in particular one of wine, blood, plasma or a fuel.

68. A filter unit as claimed in any of claims 1 to 29 wherein the fluid is a gas.

69. A filter unit as claimed in claim 68 wherein the gas is in particular one of air, oxygen, or nitrogen.

70. A filter unit assembly as claimed in any of claims 30 to 47 wherein the fluid is a liquid.

71. A filter unit assembly as claimed in claim 70 wherein the liquid is in particular one of wine, blood, plasma or a fuel.

72. A filter unit assembly as claimed in any of claims 30 to 47 wherein the fluid is a gas.

73. A filter unit as claimed in claim 72 wherein the gas is in particular one of air, oxygen, or nitrogen.

74. A filtration system as claimed in any of claims 48 to 54 or 59 to 65 wherein the fluid is a liquid.

75. A filtration system as claimed in claim 74 wherein the liquid is in particular one of wine, blood, plasma or a fuel.

76. A filtration system as claimed in any of claims 48 to 54 or 59 to 65 wherein the fluid is a gas.

77. A filtration system as claimed in claim 76 wherein the gas is in particular one of air, oxygen, or nitrogen.

78. A method as claimed in any of claims 55 to 58 wherein the fluid is a liquid.

79. A method as claimed in claim 78 wherein the liquid is in particular one of wine, blood, plasma or a fuel.

80. A method as claimed in any of claims 55 to 58 wherein the fluid is a gas.

81. A method as claimed in claim 80 wherein the gas is in particular one of air, oxygen, or nitrogen.