Abstract:
The present invention relates to a separating apparatus for separating particles from a fluid flow. Particularly, but not exclusively, the invention relates to a vacuum cleaner having such a separating apparatus for removing dust particles from a dust laden airstream. The separating apparatus includes a first cyclonic cleaning stage, a second cyclonic cleaning stage arranged downstream from the first cyclonic cleaning stage, and an elongate filter arranged downstream from the second cyclonic cleaning stage, wherein the filter is at least partially surrounded by the first cyclonic cleaning stage.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/749,137 filed Mar. 29, 2010 which claims the priority of United Kingdom Application No. 0905500.5 filed Mar. 31, 2009 and United Kingdom Application No. 0912938.8 filed Jul. 24, 2009 the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a separating apparatus for separating particles from a fluid flow. Particularly, but not exclusively, the invention relates to a vacuum cleaner having such a separating apparatus for removing dust particles from a dust laden airstream. 
       BACKGROUND OF THE INVENTION 
       [0003]    Known separating apparatus include those used in vacuum cleaners, for example cyclonic separating apparatus. Such cyclonic separating apparatus are known to comprise a low efficiency cyclone for separating relatively large particles and a high efficiency cyclone located downstream of the low efficiency cyclone for separating the fine particles which remain entrained within the airflow (see, for example, EP 0 042 723B). 
         [0004]    Irrespective of the type of separating apparatus used, there may be a risk of a small amount of dirt and dust passing through the separating apparatus and being carried to the motor-driven fan unit. It is undesirable for dirt and dust particles to pass through the fan of a motor and fan unit because the fan may become damaged or may operate less efficiently. 
         [0005]    In order to reduce this problem, some vacuum cleaners include a fine filter in an air flow path between the separating apparatus and the airflow generator. This filter is commonly known as a pre-motor filter and is used to extract any fine dirt and dust particles remaining in the air flow after it has passed through the separating apparatus. 
         [0006]    It is also known to provide a filter in an air flow path downstream of the air flow generator in order to extract any remaining dirt and dust particles prior to the air flow exiting the appliance. This type of filter is known as a post-motor filter. The post-motor filter also captures particles produced by the brushes of the motor. 
         [0007]    Filter assembly are used on the Dyson range of vacuum cleaners, for example, on model numbers DC04, DC07, DC12, DC14 and DC15. The principle by which filter assemblies of this type operate is described in GB 2349105 and EP 1239760B. 
         [0008]    In vacuum cleaner applications it is desirable for the dust separating efficiency to be as high as possible while maintaining suitable filter lifetime. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, the present invention provides a separating apparatus comprising, a first cyclonic cleaning stage, a second cyclonic cleaning stage comprising a plurality of secondary cyclones, arranged downstream of the first cyclonic cleaning stage, and an elongate filter arranged downstream of the second cyclonic cleaning stage, wherein the filter is at least partially surrounded by the first cyclonic cleaning stage. 
         [0010]    This advantageously provides a compact structure. In a preferred embodiment the filter may be a barrier filter. As used herein the term “barrier filter” shall be taken to mean a filter which captures and holds dirt and dust particles within the body of the filter. 
         [0011]    In a preferred embodiment the filter may be elongate. In other words the filter is preferably longer than it is wide. In a preferred embodiment the filter may be arranged longitudinally through the separating apparatus. Preferably the longitudinal axis of the filter may be in line with the longitudinal axis of the separating apparatus. Ideally the filter may be housed down the centre of the separating apparatus. 
         [0012]    The filter may be of any shape in cross section, for example it may be round, square or triangular in cross section. Alternatively the filter may be a sock filter. As used herein the term “sock filter” shall be taken to mean that the filter is generally tubular with a closed lower end. The filter may be deformable for example it may be made from a soft foldable material or fabric. The filter may be housed in a filter housing, for example an elongate filter housing. The filter may further comprise one or more seal, for example a seal made from a deformable material for example a plastics or rubber material. The seal is most preferably arranged such that during use of the separating apparatus all or substantially all of the air which passes out of the second cyclonic cleaning stage will pass into and through the filter. 
         [0013]    The filter may be formed from any suitable material for example glass, fleece, polyester, polypropylene, polyurethane, polytetrafluoroethylene or any other suitable plastics material. In a preferred embodiment the filter medium may be an open cell reticulated plastics foam, for example a polyurethane foam. The polyurethane foam may be derived from either polyester or polyether. 
         [0014]    In an alternative embodiment the filter may be formed from an organic material for example cotton, cellulose, paper or charcoal. 
         [0015]    The filter medium may have a pore size of from 3, or 10, or 50, or 100, or 500, or 1000 pores per inch (PPI) with a pore diameter of from 0.1 micron or 0.5 mm, or 1 mm, or 1.5 mm, or 2 mm, or 2.5 mm, or 3 mm, or 3.5 mm to 4 mm, or 4.5 mm, or 5 mm, or 5.5 mm, or 6 mm, or 6.5 mm, or 7 mm, or 7.5 mm, or 8 mm. In a particularly preferred embodiment the filter may be a HEPA filter or an ULPA filter. 
         [0016]    The pore size or type of filter medium may vary along the length of the filter medium. For example the pore size may decrease or increase in a downstream direction. Such a change in pore size may be a gradual change which occurs in a single filter medium or a plurality of sections of filter medium may be brought together to form a filter medium which has a varying pore size across it&#39;s length. Again the pore size may decrease or increase in a downstream direction, or alternatively it may vary in another random or non random way. 
         [0017]    In an alternative embodiment the filter may be an electrostatic filter, for example it may be a frictional electrostatic filter, an electret media filter or it may be an electrostatic filter connected to a high voltage power supply. In a preferred embodiment the high voltage power supply may be generated by a printed circuit board (“PCB”) which is preferably located in the separating apparatus, for example in an exhaust manifold of the separating apparatus. The PCB may however be located on the main body of a surface treating apparatus to which the separating apparatus is removably attached during use. 
         [0018]    The filter may alternatively be formed from a combination of any of the above materials. It may for example be formed from one or more layers of filter medium which may be glued, bonded or stitched together in any suitable way. 
         [0019]    Ideally the first cyclonic cleaning stage comprises a single cylindrical cyclone and a dust collecting bin. The dust collecting bin may be formed from a lower section of the cylindrical cyclone itself or it may be in the form of a separate dust collecting bin removably attached to the base of the cylindrical cyclone. 
         [0020]    The first cyclonic cleaning stage or a portion of it is arranged around the filter such that the filter is partially or totally surrounded by the first cyclonic cleaning stage. Ideally the external surface of the filter is not subject to the cyclonic airflow inside the first cyclonic cleaning stage. In other words the filter is not inside the single cylindrical cyclone, but it is housed within and surrounded by the first cyclonic cleaning stage. 
         [0021]    In a preferred embodiment the first cyclonic cleaning stage may be arranged around the second cyclonic cleaning stage or a portion of the second cyclonic cleaning stage, such that the second cyclonic cleaning stage or a portion of it is surrounded by the first cyclonic cleaning stage. In this embodiment the second cyclonic cleaning stage or a portion of it may therefore be housed within the first cyclonic cleaning stage. In a preferred embodiment the second cyclonic cleaning stage or a portion of it may be located longitudinally through the first cyclonic cleaning stage. The first cyclonic cleaning stage may therefore be annular in shape. 
         [0022]    In a particular embodiment the second cyclonic cleaning stage may comprise a plurality of secondary cyclones arranged in parallel and a dust collecting bin, which may be arranged below the secondary cyclones. In a preferred embodiment the secondary cyclones may be formed in a ring above or at least partially above the first cyclonic cleaning stage. Ideally the secondary cyclones are centered about the longitudinal axis of the first cyclonic cleaning stage. 
         [0023]    In a preferred embodiment the dust collecting bin of the second cyclonic cleaning stage may be arranged longitudinally through the separating apparatus such that it is surrounded by and housed within the first cyclonic cleaning stage. 
         [0024]    Ideally the filter is located longitudinally through the centre of the second cyclonic cleaning stage. In such an embodiment the dust collecting bin of the second cyclonic cleaning stage may also be annular in shape. In such an embodiment the first cyclonic cleaning stage, the second cyclonic cleaning stage and the filter may be arranged concentrically. Preferably they are arranged about a common central axis of the separating apparatus. Preferably the secondary cyclones surround a top portion of the filter and the dust collecting bin of the second cyclonic cleaning stage surrounds a lower portion of the filter. 
         [0025]    In a preferred embodiment the filter is separate from, but in fluid communication with, the second cyclonic cleaning stage. The term “separate from” as used herein shall be taken to mean that the filter is not subjected to the cyclonic airflow set up inside the cyclonic cleaning stages during use. 
         [0026]    The filter may be directly downstream of the second cyclonic cleaning stage or it may be in fluid communication with the second cyclonic cleaning stage via an air passage. 
         [0027]    In a particular embodiment the filter may extend from a top edge of the second cyclonic cleaning stage to at or near a base of the separating apparatus. Preferably the filter may extend along 40, or 45, or 50, or 55, or 60, or 65, or 70, or 75, to 80, or 85, or 90, or 95, or 100 percent of the distance between the top edge of the second cyclonic cleaning stage and the base of the separating apparatus. Alternatively or additionally the filter may extend from 50, or 55, or 60, or 65, or 70, to 75, or 80, or 85, or 90, or 95, or 100 percent of the length of the separating apparatus. 
         [0028]    A second aspect of the present invention provides a vacuum cleaner comprising a separating apparatus as described above. In a particular embodiment the separating apparatus may be removably mounted to a main body of the vacuum cleaner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0030]      FIG. 1  is a canister vacuum cleaner incorporating a separating apparatus according to the present invention; 
           [0031]      FIG. 2  is an upright vacuum cleaner incorporating a separating apparatus according to the present invention; 
           [0032]      FIG. 3   a  is a longitudinal section through the separating apparatus shown in  FIGS. 1 and 2 ; 
           [0033]      FIG. 3   b  is a horizontal section through the separating apparatus shown in  FIGS. 1 and 2 ; 
           [0034]      FIG. 4  is a schematic section through the electrostatic filter shown in  FIG. 3 ; 
           [0035]      FIG. 5  is a section through an alternative embodiment of a separating apparatus; 
           [0036]      FIG. 6   a  is a longitudinal section through an alternative embodiment of a separating apparatus; 
           [0037]      FIG. 6   b  is a horizontal section through the embodiment shown in  FIG. 6   a;    
           [0038]      FIG. 7  is a section through an alternative embodiment of a separating apparatus; 
           [0039]      FIG. 8   a  is a section through an alternative embodiment of separating apparatus; 
           [0040]      FIG. 8   b  is a perspective view of the cross-over duct assembly of the separating apparatus of  FIG. 8   a;    
           [0041]      FIG. 9   a  is an schematic section through a filter according to the present invention; and 
           [0042]      FIG. 9   b  is a schematic section through a filter according to the present invention. 
       
    
    
       [0043]    Like reference numerals refer to like parts throughout the specification. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0044]    With reference to  FIGS. 1 and 2  a vacuum cleaner is shown and indicated generally by the reference numeral  1 . 
         [0045]    In  FIG. 1  the vacuum cleaner  1  comprises a main body  2 , wheels  4  mounted on the main body  2  for manoeuvring the vacuum cleaner  1  across a surface to be cleaned, and a separating apparatus  6  removably mounted on the main body  2 . A hose  8  communicates with the separating apparatus  6  and a motor and fan unit (not shown) is housed within the main body  2  for drawing dust laden air into the separating apparatus  6  via the hose  8 . Commonly, a floor-engaging cleaner head (not shown) is coupled to the distal end of the hose  8  via a wand to facilitate manipulation of a dirty air inlet  10  over the surface to be cleaned. 
         [0046]    In use, dust laden air drawn into the separating apparatus  6  via the hose  8  has the dust particles separated from it in the separating apparatus  6 . The dirt and dust is collected within the separating apparatus  6  while the cleaned air is channeled past the motor for cooling purposes before being ejected from the vacuum cleaner  1 . 
         [0047]    The upright vacuum cleaner  1  shown in  FIG. 2  has a main body  2  in which a motor and fan unit (not shown) is mounted and on which wheels  4  are mounted to allow the vacuum cleaner  1  to be manoeuvred across a surface to be cleaned. A cleaner head  14  is pivotably mounted on the lower end of the main body  2  and a dirty air inlet  10  is provided on the underside of the cleaner head  14  facing the surface to be cleaned. A separating apparatus  6  is removably provided on the main body  2  and ducting  16  provides communication between the dirty air inlet  10  and the separating apparatus  6 . A wand and handle assembly  18  is releasably mounted on the main body  2  behind the separating apparatus  6 . 
         [0048]    In use, the motor and fan unit draws dust laden air into the vacuum cleaner  1  via either the dirty air inlet  10  or the wand  18 . The dust laden air is carried to the separating apparatus  6  via the ducting  16  and the entrained dust particles are separated from the air and retained in the separating apparatus  6 . The cleaned air is passed across the motor for cooling purposes and then ejected from the vacuum cleaner  1 . 
         [0049]    The separating apparatus  6  forming part of each of the vacuum cleaners  1  is shown in more detail in  FIGS. 3   a ,  3   b ,  5 ,  6   a ,  6   b  and  7 . The specific overall shape of the separating apparatus  6  can be varied according to the type of vacuum cleaner  1  in which the separating apparatus  6  is to be used. For example, the overall length of the separating apparatus  6  can be increased or decreased with respect to the diameter of the separating apparatus  6 . 
         [0050]    The separating apparatus  6  comprises a first cyclonic cleaning stage  20 , a second cyclonic cleaning stage  22  and an electrostatic filter  70  located longitudinally through the separating apparatus  6 . An embodiment of the electrostatic filter can be seen in more detail in  FIG. 4 . 
         [0051]    The first cyclonic cleaning stage  20  can be seen to be the annular chamber  38  located between the outer wall  24  which is substantially cylindrical in shape and the second cylindrical wall  36  which is located radially inwardly from the outer wall  24  and spaced from it. The lower end of the first cyclonic cleaning stage  20  is closed by a base  26  which is pivotably attached to the outer wall  24  by means of a pivot  28  and held in a closed position by a catch  30 . In the closed position, the base  26  is sealed against the lower ends of the walls  24 ,  36 . Releasing the catch  30  allows the base  26  to pivot away from the outer wall  24  and the second cylindrical wall  36  for emptying the first cyclonic cleaning stage  20  and the second cyclonic cleaning stage  22   
         [0052]    In this embodiment the top portion of the annular chamber  38  forms a cylindrical cyclone  32  of the first cyclonic cleaning stage  22  and the lower portion forms a dust collecting bin  34 . The second cyclonic cleaning stage  22  comprises  12  secondary cyclones  50  which are arranged in parallel and a second dust collecting bin  64 . 
         [0053]    A dust laden air inlet  40  is provided in the outer wall  24  of the first stage cyclone  20 . The dust laden air inlet  40  is arranged tangentially to the outer wall  24  so as to ensure that incoming dust laden air is forced to follow a helical path around the annular chamber  38 . A fluid outlet from the first cyclonic cleaning stage  20  is provided in the form of a shroud  42 . The shroud  42  comprises a cylindrical wall  44  in which a large number of perforations  46  are formed. The only fluid outlet from the first cyclonic cleaning stage  20  is formed by the perforations  46  in the shroud  42 . 
         [0054]    A passageway  48  is formed downstream of the shroud  42 . The passageway  48  communicates with the second cyclonic cleaning stage  22 . The passageway  48  may be in the form of an annular chamber which leads to inlets  52  of the secondary cyclones  50  or may be in the form of a plurality of distinct air passageways each of which leads to a separate secondary cyclone  50 . 
         [0055]    A third cylindrical wall  54  extends downwardly from a vortex finder plate  56  which forms a top surface of each of the secondary cyclones  50 , towards the base  26 . The third cylindrical wall  54  is located radially inwardly of the second cylindrical wall  36  and is spaced from it so as to form a second annular chamber  58  between them. 
         [0056]    When the base  26  is in the closed position, the third cylindrical wall  54  may reach down to and be sealed against the base  26  as shown in  FIGS. 5 and 6   a . Alternatively as shown in  FIGS. 3   a  and  7  the third cylindrical wall  54  may stop short of the base  26  and may be sealed by an electrostatic filter base plate  60 . 
         [0057]    The secondary cyclones  50  are arranged in a circle substantially or totally above the first cyclonic cleaning stage  20 . A portion of the secondary cyclones  50  may project into the top of the first cyclonic cleaning stage  20 . The secondary cyclones  50  are arranged in a ring which is centred on the axis of the first cyclonic cleaning stage  20 . Each secondary cyclone  50  has an axis which is inclined downwardly and towards the axis of the first cyclonic cleaning stage  20 . 
         [0058]    Each secondary cyclone  50  is frustoconical in shape and comprises a cone opening  62  which opens into the top of the second annular chamber  58 . In use dust separated by the secondary cyclones  50  will exit through the cone openings  62  and will be collected in the second annular chamber  58 . The second annular chamber  58  thus forms the dust collecting bin  64  of the second cyclonic cleaning stage  22 . A vortex finder  66  is provided at the upper end of each secondary cyclone  50 . The vortex finders  66  may be an integral part of the vortex finder plate  56  or they may pass through the vortex finder plate  56 . In all of the embodiments shown the vortex finders fluidly connect with the electrostatic filter  70 . 
         [0059]    In the embodiments shown in  FIGS. 3   a ,  5  and  7  the vortex finders  66  lead into vortex fingers  68  which in  FIGS. 3   a  and  5  communicate with an air passage  74  which leads to the lower end of the electrostatic filter  70  and in  FIG. 7  communicates directly with the top end of the electrostatic filter  70 . It is however possible that the vortex finders  66  could communicate with a plenum or manifold  98  which in turn communicates with an air passage or directly with the electrostatic filter  70 . In  FIG. 6   a  it can be seen that the vortex finders  66  communicate with a plenum  98  which communicates directly with the top end of the electrostatic filter  70 . 
         [0060]    In  FIGS. 3   a  and  3   b  it can be seen that the air passage  74  is arranged longitudinally down the centre of the separating apparatus  6 . The electrostatic filter  70  is arranged around the air passage  74  such that the air passage  74  is partially or totally surrounded by the electrostatic filter  70 . An upper end of the electrostatic filter  70  is fluidly connected to the exit port  96  of the separating apparatus  6  via the exhaust manifold  94 . The exhaust manifold  94  at least partially surrounds the vortex fingers  68  to form an exhaust manifold containing two fluidly distinct air passages, the first being the exhaust manifold  94  itself and the second being the vortex fingers  68 . 
         [0061]    In  FIG. 5  it can be seen that the air passage  74  is annular in shape and is at least partially surrounded by the electrostatic filter  70 . The air passage  74  is arranged to provide a fluid passageway, or individual fluid passageways to the lower end of the electrostatic filter  70 . An exhaust passage  100  provides a fluid passageway between the upper end of the electrostatic filter  70  and the exit port  96  which is located on a lower end of the separating apparatus  6 . The exhaust passage  100  is arranged longitudinally down the centre of the separating apparatus  6 . The air passage  74  is arranged around the exhaust passage  100  such that the exhaust passage  100  is partially or totally surrounded by the air passage  74 . 
         [0062]    In  FIG. 6   a  it can be seen that the plenum  98  fluidly connects the vortex finders  66  and the electrostatic filter  70 . A lower end of the electrostatic filter  70  is fluidly connected to the exit port  96  of the separating apparatus  6  which is located at a lower end of the separating apparatus  6 . In this embodiment there is no air passage or exhaust passage. 
         [0063]    In  FIG. 7  it can be seen that the vortex fingers  68  lead directly to the electrostatic filter  70 . An annular exhaust passage  100  is arranged around the electrostatic filter  70  such that the electrostatic filter  70  is arranged longitudinally down the centre of the separating apparatus  6  and is partially or totally surrounded by the annular exhaust passage  100 . An upper end of the annular exhaust passage  100  is fluidly connected to the exit port  96  of the separating apparatus  6  via the exhaust manifold  94  located at an upper end of the separating apparatus  6 . Again the exhaust manifold  94  at least partially surrounds the vortex fingers  68  to form an exhaust manifold  94  containing two fluidly distinct air passages, the first being the exhaust manifold  94  itself and the second being the vortex fingers  68 . 
         [0064]    In all of the embodiments described above the electrostatic filter  70  is arranged longitudinally down the separating apparatus  6  such that the secondary cyclones  50  and at least a portion of the dust collecting bin  64  surround the electrostatic filter  70 . It can be seen that the secondary cyclones  50  surround a top portion of the electrostatic filter  70  and the dust collecting bin  64  surrounds a lower portion of the electrostatic filter  70 . It can also be seen that the electrostatic filter  70  extends from the vortex finder plate  56  to near the base  26 . 
         [0065]    In the embodiment shown in  FIGS. 3   a ,  3   b ,  4  and  5  the electrostatic filter  70  comprises concentrically arranged cylindrical first, second and third electrodes  76 ,  78 ,  80 . A filter medium  82  is located between both the first and second electrodes  76 ,  78  and the second and third electrodes  78 ,  80 . 
         [0066]    The electrostatic filter  70  also comprises a corona discharge device in the form of a corona discharge electrode  84  and two electrodes of low curvature  86 . The electrostatic filter  70  would however function without the corona discharge device. 
         [0067]    The first electrode of low curvature  86  is an extension of the first electrode  76  below a lower surface  88  of the filter medium  82  and the second electrode of low curvature  86  is an extension of the third electrode  80  below the lower surface  88  of the filter medium  82 . 
         [0068]    The corona discharge electrode  84  is in the form of a serrated lower edge  90  of the second electrode  78  which extends below the lower surface  88  of the filter medium  82 . The electrodes of low curvature  86  can be seen to project both upstream and downstream of the serrated lower edge  90  of the corona discharge electrode  84 . 
         [0069]    The first and third electrodes  76 ,  80  are at 0 Volts and the second electrode  78  is at from −4 to −10 kV. The electrodes  76 ,  78 ,  80  are connected to a high voltage power supply. The high voltage power supply is generated by a PCB  93  which is preferably located in an exhaust manifold  94 . 
         [0070]    The electrodes  76 ,  78 ,  80  may be formed from any suitable conductive material, for example aluminium. 
         [0071]    In the embodiment shown in  FIGS. 6   a  and  6   b  the electrostatic filter  70  comprises a plurality of first and second flat plate electrodes  76 ,  78  which are arranged in parallel. 
         [0072]    Filter media  82  is located between each adjacent first and second electrodes  76 ,  78  to form a layered electrostatic filter  70 . The electrostatic filter  70  may be any shape in cross section but is preferably cylindrical. The first and second electrodes  76 ,  78  are arranged inside the third cylindrical wall  54  which provides a tubular passageway which forms an outer surface of the electrostatic filter  70 . The first and second electrodes  76 ,  78  are arranged longitudinally to provide a plurality of parallel air passages which run longitudinally through the electrostatic filter  70 . 
         [0073]    The electrostatic filter  70  also comprises a corona discharge device in the form of corona discharge electrodes  84  and electrodes of low curvature  86 . The electrostatic filter  70  would however function without the corona discharge device. Each electrode of low curvature  86  is an extension of a first electrode  76  above the upper surface  102  of the filter media  82 . The corona discharge electrodes  84  are in the form of serrated upper edges  91  of the second electrodes  78  which extend above the upper surfaces  102  of the filter medium  82 . The electrodes of low curvature  86  can be seen to project both upstream and downstream of the serrated upper edges  91  of the corona discharge electrodes  84 . 
         [0074]    The first electrodes  76  are at 0 Volts and the second electrodes  78  are at from −4 to −10kV. The electrodes  76 ,  78  are connected to a high voltage power supply. 
         [0075]    In  FIG. 7  it can be seen that the electrostatic filter  70  described above has been replaced with an alternative type of electrostatic filter  70 . In this embodiment the electrostatic filter  70  may be a frictional electrostatic filter or an electret medium electrostatic filter  70 . Alternatively it may be any other suitable type of filter, for example a filter formed from a plastics and/or an organic material. 
         [0076]    This electrostatic filter  70  could of course be replaced by an electrostatic filter  70  as described in relation to  FIGS. 3   a ,  3   b ,  4 ,  5 ,  6   a  and  6   b . Equally the electrostatic filter  70  described in  FIGS. 3   a ,  3   b ,  4 ,  5 ,  6   a  and  6   b  could be replaced with a different type of filter  70 , for example a frictional electrostatic filter, electret medium filter, a filter formed from a plastics and/or organic matter. 
         [0077]    During use of the embodiments described above dust laden air enters the separating apparatus  6  via the dust laden air inlet  40  and, because of the tangential arrangement of the inlet  40 , the dust laden air follows a helical path around the outer wall  24 . Larger dirt and dust particles are deposited by cyclonic action in the annular chamber  38  and collected in the dust collecting bin  34 . The partially-cleaned dust laden air exits the annular chamber  38  via the perforations  46  in the shroud  42  and enters the passageway  48 . The partially-cleaned dust laden air then passes into tangential inlets  52  of the secondary cyclones  50 . Cyclonic separation is set up inside the secondary cyclones  50  so that separation of some of the dust particles which are still entrained within the airflow occurs. The dust particles which are separated from the airflow in the secondary cyclones  50  are deposited in the second annular chamber  58  which forms at least part of the dust collecting bin  64  of the second cyclonic cleaning stage  22 . The further cleaned dust laden air then exits the secondary cyclones  50  via the vortex finders  66 . The further cleaned dust laden air then passes into the electrostatic filter  70 . 
         [0078]    In the embodiment shown in  FIGS. 3   a  and  3   b , the further cleaned dust laden air passes out of the vortex finders  66 , along the vortex fingers  68  and down the air passage  74  towards the lower end of the electrostatic filter  70 . The air then travels past the corona discharge device formed from the corona discharge electrode  84  and the electrodes of low curvature  86  such that any dust particles remaining in the further cleaned dust laden air become charged. The further cleaned dust laden air containing the charged dust then travels upwardly through the filter medium  82 . A potential difference is generated across the filter medium  82  causing the charged dust particles to be attracted to respective positive and negative ends of the filter medium  82 , thus trapping them within the filter medium  82 . 
         [0079]    The cleaned air then leaves the top of the electrostatic filter  70  via apertures  92  in the vortex finder plate  56  and enters the exhaust manifold  94 . The cleaned air then exhausts the separating apparatus  6  via the exit port  96 . 
         [0080]    In the embodiment shown in  FIG. 5 , the further cleaned dust laden air passes out of the vortex finders  66 , along the vortex fingers  68  and down the air passage  74  towards the bottom end of the electrostatic filter  70 . The air then travels past the corona discharge device formed from the corona discharge electrode  84  and the electrodes of low curvature  86  such that any dust particles remaining in the further cleaned dust laden air become charged. The further cleaned dust laden air containing the charged dust then travels upwardly through the filter medium  82 . A potential difference is generated across the filter medium  82  causing the charged dust particles to be attracted to respective positive and negative ends of the filter medium  82 , thus trapping them within the filter medium  82 . 
         [0081]    The cleaned air then leaves the top of the electrostatic filter  70  and enters the exhaust passage  100  which directs air downwardly through the centre of the separating apparatus  6  to the exit port  96  which is located on the lower end of the separating apparatus  6 . 
         [0082]    In the embodiment shown in  FIGS. 6   a  and  6   b , the further cleaned dust laden air passes out of the vortex finders  66  and enters the plenum  98 . The air passes through the plenum  98  and enters the top of the electrostatic filter  70 . The air then travels past the corona discharge device formed from the corona discharge electrode  84  and the electrodes of low curvature  86  such that any dust particles remaining in the further cleaned dust laden air become charged. The further cleaned dust laden air containing the charged dust then travels downwardly through the filter medium  82 . A potential difference is generated across the filter medium  82  causing the charged dust particles to be attracted to respective positive and negative ends of the filter medium  82 , thus trapping them within the filter medium  82 . 
         [0083]    The cleaned air then leaves the lower end of the electrostatic filter  70  and exhausts the separating apparatus  6  via the exit port  96  located on the lower end of the separating apparatus  6 . 
         [0084]    In the embodiment shown in  FIG. 7 , the further cleaned dust laden air passes out of the vortex finders  66 , along the vortex fingers  68  and into the electrostatic filter  70 . The further cleaned dust laden air travels downwardly through electrostatic filter  70 . The cleaned air then leaves the lower end of the electrostatic filter  70  and travels up the exhaust passage  100  to exit the separating apparatus  6  via the exit port  96  located on the upper end of the separating apparatus  6 . 
         [0085]    It will be appreciated from the description that the separating apparatus  6  includes two distinct stages of cyclonic separation and a distinct stage of electrostatic filtration. The first cyclonic cleaning stage  20  comprises a single cylindrical cyclone  32 . The relatively large diameter of the outer wall  24  of which means that comparatively large particles of dirt and debris will be separated from the air because the centrifugal forces applied to the dirt and debris are relatively small. Some fine dust will be separated as well. A large proportion of the larger debris will reliably be deposited in the dust collecting bin  34 . 
         [0086]    There are  12  secondary cyclones  50 , each of which has a smaller diameter than the cylindrical cyclone  32  and so is capable of separating finer dirt and dust particles than the cylindrical cyclone  32 . They also have the added advantage of being challenged with air which has already been cleaned by the cylindrical cyclone  32  and so the quantity and average size of entrained dust particles is smaller than would otherwise have been the case. The separation efficiency of the secondary cyclones  50  is considerably higher than that of the cylindrical cyclone  32  however some small particles will still pass through the secondary cyclones  50  to the electrostatic filter  70 . 
         [0087]    In all of the embodiments described above the filter medium  82  may be formed from any suitable material for example an open cell reticulated polyurethane foam derived from a polyester. 
         [0088]    The filter medium  82  has a pore size in the range of 6 to 12 PPI and preferably 8 to 10 PPI. The pore size of the filter medium  82  shown in  FIG. 3  varies along its length because it is formed from two sections each having a different pore size. In the embodiment shown in  FIG. 4  the upstream portion has a pore size of 8 PPI and the downstream portion has a pore size of 10 PPI. 
         [0089]    A further embodiment is shown in  FIG. 8 . In this embodiment it can be seen that the separating apparatus comprises a filter  136 . The filter comprises a rim  600 , a base cap  602 , and four cylindrical filter members located between the rim  600  and the base cap  602 . The filter  136  is generally cylindrical in shape, and comprises a central open chamber  612  bounded by the rim  600 , the base cap  602  and an innermost, first filter member  604 . 
         [0090]    The filter  136  is constructed such that it is pliable, flexible and resilient. The rim  600  is annular in shape having a width, W in a direction Z perpendicular to the axis X. The rim  600  is manufactured from a material with a hardness and deformability that enable a user to deform the rim  600  (and thus the filter  136 ) by pressing or grasping the rim  600  and twisting and squeezing the filter  136  by hand, in particular during a washing operation. In this embodiment, the rim  600  and base cap  602  are formed from polyurethane. 
         [0091]    Each filter member of the filter  136  is manufactured with a rectangular shape. The four filter members are then joined and secured together along their longest edge by stitching, gluing or other suitable technique so as to form a pipe length of filter material having a substantially open cylindrical shape. An upper end of each cylindrical filter member is then bonded to the rim  600 , while a lower end of each filter member is bonded to the base cap  602 , preferably by over-moulding the polyurethane material of the rim  600  and base cap  602  during manufacture of the filter assembly  136 . Alternative manufacturing techniques for attaching the filter members include gluing, and spin-casting polyurethane around the upper and lower ends of the filter members. In this way the filter members are encapsulated by polyurethane during the manufacturing process to produce a strengthened arrangement capable of withstanding manipulation and handling by a user, particularly during washing of the filter  136 . 
         [0092]    The first filter member  604  comprises a layer of scrim or web material having an open weave or mesh structure. A second filter member  606  surrounds the first filter member  604 , and is formed from a non-woven filter medium such as fleece. The shape and volume of the second filter member  606  is selected so as to substantially fill the volume delimited by the width, W, of rim  600  and the height of the filter  136 . Therefore, the width of the second filter member  606  is substantially the same as the width, W, of the rim  600 . 
         [0093]    The third filter member  608  surrounds the second filter member  606 , and comprises an electrostatic filter medium covered on both sides by a protective fabric. The layers are held together in a known manner by stitching or other seal. 
         [0094]    The fourth filter member  610  surrounds the third filter member  608 , and comprises a layer of scrim or web material having an open weave or mesh structure. 
         [0095]    During manufacture an upper part of the first filter member  604  is bonded to the rim  600  and the base cap  602  immediately adjacent the second filter member  606 . An upper part of the third filter member  608  is bonded to the rim  600  and the base cap  602  immediately adjacent the second filter member  606 , and an upper part of the fourth filter member  610  is bonded to the rim  600  and the base cap  602  immediately adjacent the third filter member  608 . In this manner the filter members  604 ,  606 ,  608 ,  610  are held in position in the filter assembly  136  with respect to the rim  600  and the base cap  602  such that an airflow will impinge first on the first filter member, before impinging, in turn, on the second, third and fourth filter members. For the third filter member  608 , comprising an electrostatic filter medium covered on both sides by a protective fabric, it is preferred that all of the layers of the third filter member  608  are bonded to the rim  600  and the base cap  602  so that the risk of delamination of the second filter member  606  during use is reduced. 
         [0096]    In this embodiment during use, once the air has passed out of the second cyclonic cleaning stage  22  it passes through the central open chamber  612 , and is forced tangentially outwardly towards the filter members of the filter  136 . The airflow enters the first filter member  604  first, and then passes sequentially through the second filter member  606 , the third filter member  608  and the fourth filter member  610 , with dirt and dust being removed from the air flow as it passes through each filter member. 
         [0097]    The airflow emitted from the filter  136  passes into the cylindrical chamber  132  and is drawn into the filter outlet ducts  176  to exit at the top end  72  of the separating apparatus. 
         [0098]    Because of the arrangement of the filter  136  in this embodiment the separating apparatus further comprises a cross-over duct assembly  138 . The cross-over duct assembly  138  is shown in  FIG. 8   b  and comprises an annular seal  162  and a cross-over duct  164 . In the preferred embodiment the seal  162  is rubber, and is secured around the outer surface of the cross-over duct  164  with a friction fit. The cross-over duct  164  comprises an upper portion and a lower portion. The seal  162  is located on an upper portion of the cross-over duct  164 . The upper portion of the cross-over duct  164  comprises a generally cup shaped portion  166  which provides a fluid outlet from the separating apparatus, and which has a convex, preferably hemispherical outer surface. The lower portion of the cross-over duct  164  comprises a lip  168  and a cylindrical outer housing  170  shaped to correspond to the size and shape of the cylindrical chamber  132 . The lip  168  is shaped to have a diameter slightly larger than that of the cylindrical outer housing  170  and is located towards the upper end of the cylindrical outer housing  170 . An inlet chamber  172  is formed between the upper portion and the lower portion of the cross-over duct  164 . The inlet chamber  172  is bounded by the lower surface of the cup shaped portion  166 , the upper surface of the cylindrical outer housing  170  and the lip  168 . 
         [0099]    The cross-over duct  164  comprises a first set of ducts in which air passes in a first direction through the cross-over duct  164 , and a second set of ducts in which air passes in a second direction, different from the first direction, through the cross-over duct  164 . In this embodiment, eight ducts are located within the cylindrical outer housing  170  of the cross-over duct  164 . These ducts comprise a first set of four filter inlet ducts  174 , and a second set of four filter outlet ducts  176 . The filter inlet ducts  174  are arranged in an annular formation which is centred on the axis X and in which the filter inlet ducts  174  are evenly spaced. The filter outlet ducts  176  are similarly evenly arranged and spaced about the axis X, but are angularly offset from the filter inlet ducts  174  by an angle of around 45 degrees. 
         [0100]    With reference to  FIG. 8   a  the vortex fingers  68  communicate with the cross-over duct assembly  138 . The outlet of each vortex finger  68  terminates at the inlet chamber  172  of the cross-over duct assembly  138 . 
         [0101]    Each filter inlet duct  174  has an inlet opening located towards the upper surface of the cylindrical outer housing  170  and adjacent the inlet chamber  172 , and an outlet opening located towards the base of the cylindrical outer housing  170 . Each filter inlet duct  174  comprises a passage  184  extending between the inlet opening and the outlet opening. The passage  184  has a smoothly changing cross-section for reducing noise and turbulence in the airflow passing through the cross-over duct  164 . 
         [0102]    Each filter outlet duct  176  comprises an inlet opening  188  in the outer surface of the cylindrical outer housing  170 , and an exit port  190  for ducting cleaned air away from the filter assembly  136 . A passage  186  extending between the inlet opening  188  and the exit port  190  passes through the cylindrical outer housing  170  from the outer surface of the cylindrical outer housing  170  towards the axis X. Consequently, the exit port  190  is located closer to the axis X than the outer opening  188 . The exit port  190  is preferably circular in shape. 
         [0103]    In  FIGS. 9   a  and  9   b  alternative arrangements are shown. In these embodiments the first and second cyclonic cleaning stages have been removed. The filters  136  would be positioned in the same position as the filter  136  shown in  FIG. 8 . However the cross over duct described above would not be required. 
         [0104]    In the embodiment shown in  FIG. 9   a , air traveling from the second cyclonic cleaning stage travels down an outer air pathway  650  which surrounds the filter  136 . The air then passes through the filter  136  and then exits the top of the filter  136  via a central exhaust passage  652 . 
         [0105]    In the embodiment shown in  FIG. 9   b  the air traveling from the second cyclonic cleaning stage passes through the central open chamber  612 , and is forced tangentially outwardly towards the filter members of the filter assembly  132 . In this embodiment the airflow emitted from the filter  136  passes into the outer cylindrical chamber  132  towards an exit port  96  at the lower end  72  of the separating apparatus.