Abstract:
The invention provides a cyclonic separating apparatus that includes a plurality of cyclones, each having an inlet and being arranged in parallel with one another, and a passageway arranged upstream of the cyclones for carrying an airflow to the inlets of the cyclones, wherein dividers are provided in the passageway for dividing the airflow within the passageway into a number of separate flowpaths, the number of flowpaths being equal to the number of cyclones, and wherein the cross-sectional area of each flowpath ( 142   a ), decreases along the direction of air flow. The invention also provides a method of operating a cyclonic separating apparatus ( 100 ) comprising a plurality of cyclones ( 104 ), each having an inlet and being arranged in parallel with one another, and a passageway ( 142 ) arranged upstream of the cyclones ( 104 ), the method comprising the steps of:(a) introducing a flow of dirt-laden air to the passageway ( 142 ); (b) dividing the flow of dirt-laden air into a plurality of airflow portions, the number of airflow portions being equal to the number of cyclones ( 104 ); and (c) reducing the cross-sectional area of each of the airflow portions in the direction of flow of the dirt-laden air.

Description:
FIELD OF THE INVENTION 
   The invention relates to cyclonic separating apparatus, particularly but not exclusively to cyclonic separating apparatus for use in vacuum cleaners. The invention also relates to a method of operating cyclonic separating apparatus of the aforementioned type. 
   BACKGROUND OF THE INVENTION 
   Cyclonic separating apparatus is well known and has uses in a wide variety of applications. Over the last decade or so, the use of cyclonic separating apparatus to separate particles from an airflow in a vacuum cleaner has been developed and introduced to the market. Detailed descriptions of cyclonic separating apparatus for use in vacuum cleaners are given in, inter alia, U.S. Pat. No. 3,425,192, U.S. Pat. No. 4,373,228 and EP 0 042 723. From these and other prior art documents, it can be seen that it is known to provide two cyclone units in series so that the airflow passes sequentially through at least two cyclones. This allows the larger dirt and debris to be extracted from the airflow in the first cyclone, leaving the second cyclone to operate under optimum conditions and so effectively to remove very fine particles in an efficient manner. This type of arrangement has been found to be effective when dealing with airflows in which is entrained a variety of matter having a wide particle size distribution. Such is the case in vacuum cleaners. 
   It is also known to provide cyclonic separating apparatus in which a plurality of cyclones are arranged in parallel with one another, as in, for example, U.S. Pat. No. 2,874,801. Furthermore, it is known to provide such a plurality of parallel cyclones downstream of a single cyclone, as in, for example, U.S. Pat. No. 3,425,192. However, the entries to these parallel cyclones are commonly via a plenum chamber with which the inlets to the parallel cyclones communicate in a direct manner. Other arrangements of parallel cyclones include uniform ducts leading from a plenum chamber to the inlet of each cyclone: see, for example, U.S. Pat. No. 3,682,302. 
   The passage of the air through a plenum chamber often causes unnecessary pressure losses because the relatively small inlets to the parallel cyclones bring about sudden and quite dramatic changes in the cross-section of the airflow path along which the air is flowing. The overall efficiency of the cyclonic separating apparatus is therefore lower than necessary. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide cyclonic separating apparatus comprising a plurality of cyclones arranged in parallel in which the air is presented to the inlets of the parallel cyclones with the minimum of pressure drop. It is a further object of the present invention to provide cyclonic separating apparatus comprising a plurality of cyclones arranged in parallel and having an improved inlet arrangement to the cyclones. It is a further object of the invention to provide cyclonic separating apparatus comprising a plurality of cyclones arranged in parallel in which the losses associated with the inlets to the cyclones are minimised. It is a further object of the invention to provide cyclonic separating apparatus comprising a plurality of cyclones arranged in parallel having an improved efficiency. 
   The invention provides cyclonic separating apparatus comprising a plurality of cyclones, each having an inlet and being arranged in parallel with one another, and a passageway arranged upstream of the cyclones for carrying an airflow to the inlets of the cyclones, wherein dividing means are provided in the passageway for dividing the airflow within the passageway into a number of separate flowpaths, the number of flowpaths being equal to the number of cyclones, and wherein the cross-sectional area of each flowpath decreases in the direction of flow therealong. 
   The arrangement allows the cross-sectional area of the flowpaths to be decreased gradually and in a controlled manner so that the losses associated with changes in cross-sectional area are minimised. Thus the losses previously associated with the inlet arrangement to a plurality of cyclones arranged in parallel can be kept to a minimum and this allows the overall efficiency of the cyclonic separation apparatus to be improved. Sudden changes to the cross-sectional area are avoided which leads to less turbulent flow and fewer losses. 
   It is advantageous if each flowpath remains separate from the remaining flowpaths between the point in the passageway at which the airflow is divided and the inlet of the respective cyclone. This discourages turbulent airflow along the flowpaths. It is also advantageous for the flowpaths to be the same length between the point in the passageway at which the airflow is divided and the inlet of the respective cyclone so as to discourage pressure differences between the cyclones. 
   In a preferred arrangement, the length of each flowpath is at least three, preferably four, more preferably five, times the effective radius of the flowpath at the inlet to the respective cyclone. This allows the cross-sectional area of each flowpath to be decreased gradually along the length thereof. In a preferred arrangement, the cross-sectional area of each flowpath decreases at a substantially constant rate along the length thereof. 
   It is advantageous for the cross-sectional area of each flowpath at the inlet to the respective cyclone to be no more that 40%, more advantageously 30%, still more advantageously 20%, of the cross-sectional area of the flowpath at the point in the passageway at which the airflow is divided. This arrangement ensures that the velocity of the airflow at the inlet to the respective cyclone is sufficiently high to ensure good separation efficiency in the cyclone. 
   Preferably, the dividing means comprise a plurality of barrier portions arranged in the passageway. The reduction in the cross-sectional area of the flowpaths is advantageously achieved by adjacent barrier portions approaching one another in the direction of flow along the passageway. In addition, each barrier portion incorporates a cyclone entry duct at or adjacent the downstream end thereof. These features, individually and in combination, allow the apparatus according to the invention to be manufactured for use. 
   The apparatus described above is advantageously put to use in a vacuum cleaner, more preferably a domestic vacuum cleaner. For packaging reasons, the number of cyclones and flowpaths which can be accommodated is limited; however, it is preferred that the number of cyclones and flowpaths is at least five, more preferably seven. It is also preferred that an upstream cyclone is arranged upstream of the cyclones. This allows the incoming airstream to be pre-cleaned by the upstream cyclone before entering the cyclones. The cyclones are thus able to operate under optimum conditions. 
   The invention also provides a method of operating cyclonic separating apparatus comprising a plurality of cyclones, each having an inlet and being arranged in parallel with one another, and a passageway arranged upstream of the cyclones, the method comprising the steps of:
     (a) introducing a flow of dirt-laden air to the passageway;   (b) dividing the flow of dirt-laden air into a plurality of flowpaths, the number of flowpaths being equal to the number of cyclones; and   (c) reducing the cross-sectional area of each of the flowpaths in the direction of flow of the dirt-laden air.   

   The method allows the cross-sectional area of the flowpaths to be decreased gradually and in a controlled manner so that the losses associated with changes in cross-sectional area are minimised, resulting in increased efficiency of the cyclonic separating apparatus. 
   It is preferred that the cross-sectional area of each flowpath is reduced by at least 60%, preferably at least 70%, more preferably at least 80%, before the dirt-laden air reaches the inlet of the respective cyclone. This ensures that the velocity of the airflow at the inlet to the respective cyclone is sufficiently high to ensure good separation efficiency in the cyclone. It is also preferred, although not essential, that the cross-sectional area of each flowpath is reduced at a substantially constant rate so as to encourage smooth airflow along each flowpath, resulting in reduced losses. 
   In a preferred embodiment, the dirt-laden air is passed through an upstream cyclone before being passed to the passageway. This allows the cyclones to operate under optimum conditions by virtue of the fact that the upstream cyclone will remove larger dirt and debris from the dirt-laden air before it passes into the cyclones. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described with reference to the accompanying drawings, wherein: 
       FIGS. 1   a  and  1   b  are front and side views, respectively, of a vacuum cleaner incorporating cyclonic separating apparatus according to the invention; 
       FIGS. 2   a  and  2   b  are front and plan views, respectively, of cyclonic separating apparatus forming part of the vacuum cleaner of  FIGS. 1   a  and  1   b;    
       FIG. 3  is a sectional side view of the cyclonic separating apparatus of  FIGS. 2   a  and  2   b , taken along the line III—III of  FIG. 2   a ; and 
       FIG. 4  is a side view, on an enlarged scale, of a part of the cyclonic separating apparatus of  FIGS. 2   a ,  2   b  and  3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1   a  and  1   b  show a domestic vacuum cleaner  10  incorporating cyclonic separating apparatus according to the present invention. The vacuum cleaner  10  comprises an upstanding body  12  at a lower end of which is located a motor casing  14 . A cleaner head  16  is mounted in an articulated fashion on the motor casing  14 . A suction inlet  18  is provided in the cleaner head  16  and wheels  20  are rotatably mounted on the motor casing  14  to allow the vacuum cleaner  10  to be manoeuvered over a surface to be cleaned. 
   Cyclonic separating apparatus  100  is mounted on the upstanding body  12  above the motor casing  14 . The cyclonic separating apparatus  100  is seated on a generally horizontal surface formed by a filter cover  22 . The filter cover  22  is located above the motor casing  14  and provides a cover for a post-motor filter (not shown). The cyclonic separating apparatus  100  is also secured to the upstanding body  12  by means of a clip  24  located at the top of the cyclonic separating apparatus  100 . The upstanding body  12  incorporates upstream ducting (not shown) for carrying dirty air to an inlet of the cyclonic separating apparatus  100  and downstream ducting  26  for carrying cleaned air away from the cyclonic separating apparatus  100 . 
   The upstanding body  12  further incorporates a hose and wand assembly  28  which may be retained in the configuration shown in the drawings so as to function as a handle for manoeuvering the vacuum cleaner  10  over a surface to be cleaned. Alternatively, the hose and wand assembly  28  may be released to allow the distal end  28   a  of the wand to be used in conjunction with a floor tool (not shown) to perform a cleaning function, eg on stairs, upholstery, etc. The structure and operation of the hose and wand assembly  28  is not material to the present invention and will not be described any further here. The general structure and operation of the hose and wand assembly  28  illustrated in  FIGS. 1   a  and  1   b  is similar to that described in U.S. Pat. No. Re 32,257 which is incorporated herein by reference. Also, several tools and accessories  30   a ,  30   b ,  30   c , are releasably mounted on the upstanding body  12  for storage purposes between periods of use. 
   The precise details of the features of the vacuum cleaner  10  described above are not material to the present invention. The invention is concerned with the details of the cyclonic separation apparatus  100  forming part of the vacuum cleaner  10 . In order for the cyclonic separation apparatus  100  to be brought into operation, the motor located in the motor casing  14  is activated so that air is drawn into the vacuum cleaner via either the suction inlet  18  or the distal end  28   a  of the hose and wand assembly  28 . This dirty air (being air having dirt and dust entrained therein) is passed to the cyclonic separation apparatus  100  via the upstream ducting. After the air has passed through the cyclonic separation apparatus  100 , it is ducted out of the cyclonic separating apparatus  100  and down the upstanding body  12  to the motor casing  14  via the downstream ducting  26 . The cleaned air is used to cool the motor located in the motor casing  14  before being exhausted from the vacuum cleaner  10  via the filter cover  22 . 
   This principle of operation of the vacuum cleaner  10  is known from the prior art. This invention is concerned with the cyclonic separation apparatus  100  which is illustrated in  FIGS. 2   a ,  2   b  and  3  in isolation from the vacuum cleaner  10 . 
   The cyclonic separation apparatus  100  illustrated in  FIGS. 2   a ,  2   b  and  3  comprises an upstream cyclone unit  101  consisting of a single upstream cyclone  102  and a downstream cyclone unit  103  consisting of a plurality of downstream cyclones  104 . The upstream cyclone  102  consists essentially of a cylindrical bin  106  having a closed base  108 . The open upper end  110  of the cylindrical bin abuts against a circular upper moulding  112  which defines an upper end of the upstream cyclone  102 . An inlet port  114  is provided in the cylindrical bin  106  in order to allow dirty air to be introduced to the interior of the upstream cyclone  102 . The inlet port  114  is shaped, positioned and configured to communicate with the upstream ducting which carries dirt-laden air from the cleaner head  16  to the cyclonic separating apparatus  100 . A handle  116  and a catch  118  are provided on the cylindrical bin  106  and the upper moulding  112  respectively in order to provide means for releasing the cylindrical bin  106  from the upper moulding  112  when the cylindrical bin  106  requires to be emptied. A seal (not shown) can be provided between the cylindrical bin  106  and the upper moulding  112  if required. 
   The base  108  of the cylindrical bin can be hingedly connected to the remainder of the cylindrical bin in order to provide further access to the interior of the cylindrical bin  106  for emptying purposes if required. The embodiment illustrated herein will include a mechanism for allowing the base  108  to be hingedly opened in order to allow emptying, but the details of such a mechanism form the subject of a copending application and will not be described for any reason other than explanation of the drawings. 
   Seven identical downstream cyclones  104  are provided in the downstream cyclone unit  103 . The downstream cyclones  104  are equi-angularly spaced about the central longitudinal axis  150  of the downstream cyclone unit  103 , which is coincident with the longitudinal axis of the upstream cyclone unit  101 . The arrangement is illustrated in  FIG. 3 . Each downstream cyclone  104  is frusto-conical in shape with the larger end thereof located lowermost and the smaller end uppermost. Each downstream cyclone  104  has a longitudinal axis  148  (see  FIG. 3 ) which is inclined slightly towards the longitudinal axis  150  of the downstream cyclone unit  103 . This feature will be described in more detail below. Also, the outermost point of the lowermost end of each downstream cyclone  104  extends radially further from the longitudinal axis  150  of the downstream cyclone unit  103  than the wall of the cylindrical bin  106 . The uppermost ends of the downstream cyclones  104  project inside a collection moulding  120  which extends upwardly from the surfaces of the downstream cyclones  104 . The collection moulding  120  supports a handle  122  by means of which the entire cyclonic separation apparatus  100  can be transported. A catch  124  is provided on the handle  122  for the purposes of securing the cyclonic separation apparatus  100  to the upstanding body  12  at the upper end thereof. An outlet port  126  is provided in the upper moulding  112  for conducting cleaned air out of the cyclonic separating apparatus  100 . The outlet port  126  is arranged and configured to co-operate with the downstream ducting  26  for carrying the cleaned air to the motor casing  14 . 
   The collection moulding  120  also carries an actuating lever  128  designed to activate a mechanism for opening the base  108  of the cylindrical bin  106  for emptying purposes as mentioned above. 
   The internal features of the upstream cyclone  102  include an internal wall  132  extending the entire length thereof. The internal space defined by the internal wall  132  communicates with the interior of the collection moulding  120  as will be described below. The purpose of the internal wall  132  is to define a collection space  134  for fine dust. Located inside the internal wall  132  and in the collection space  134  are components for allowing the base  108  to open when the actuating lever  128  is actuated. The precise details and operation of these components is immaterial to the present invention and will not be described any further here. 
   Mounted externally of the internal wall  132  are four equi-spaced baffles or fins  136  which project radially outwardly from the internal wall  132  towards the cylindrical bin  106 . These baffles  136  assist with the deposition of large dirt and dust particles in the collection space  138  defined between the internal wall  132  and the cylindrical bin  106  adjacent the base  108 . The particular features of the baffles  136  are described in more detail in WO 00/04816. 
   Located outwardly of the internal wall  132  in an upper portion of the upstream cyclone  102  is a shroud  140 . The shroud extends upwardly from the baffles  136  and, together with the internal wall  132 , defines an air passageway  142 . The shroud  140  has a perforated portion  144  allowing air to pass from the interior of the upstream cyclone  102  to the air passageway  142 . The air passageway  142  communicates with the inlet  146  of each of the downstream cyclones  104 . Each inlet  146  is arranged in the manner of a scroll so that air entering each downstream cyclone  104  is forced to follow a helical path within the respective downstream cyclone  104 . 
   Inside the passageway  142  are a plurality of barrier members  170 . The barrier members  170  are arranged between the upper portion of the shroud  140  and the upper portion of the internal wall  132  and are equi-spaced about the axis  150 . Seven barrier members  170  are provided in total.  FIG. 4  is a side view of the upper portion of the internal wall and four of the seven barrier members  170  showing the relationship of the barrier members  170  to one another and to the upper portion of the internal wall  132 . The upper portion of the shroud  140  has been omitted from  FIG. 4  for the sake of clarity. However, when the barrier members  170  are located in the separating apparatus  100  as described, the radially outermost walls  172  of each barrier member  170  (shown shaded in  FIG. 4 ) will either abut against or be formed integrally with the shroud  140 . Each barrier member  170  comprises a radially outermost wall  172  (as described above) and side walls  174   a ,  174   b  which extend between the radially outermost wall  172  and the surface of the internal wall  132 . The radially outermost wall  172  is generally triangular in shape with the tapering end pointing downwards. The side walls  174   a ,  174   b  meet to form a sharp edge  176  adjacent the tapering end of the radially outermost wall  172  so as to give each barrier member  170  a generally wedge-shaped configuration. The barrier members  170  and their arrangement between the shroud  140  and the internal wall  132  and about the axis  150  cause the downstream portion of the passageway  142  to be divided into seven flowpaths  142   a . Each flowpath  142   a  is located between a pair of adjacent barrier members  170  and is substantially identical in length and configuration to the remaining flowpaths  170 . The generally wedge-shaped configuration of the barrier members  170  means that the cross-sectional area of each flowpath  142   a  decreases in a direction away from the sharp edge  176 . The rate of decrease of the cross-sectional area of each flowpath  142   a  is substantially constant, at least over the majority of the length thereof. 
   Each flowpath  142   a  includes, at its downstream end, a cyclone entry duct  178  which opens into the respective cyclone  104  via a cyclone inlet. The cyclone inlet is the point in the duct  178  furthest downstream at which the duct  178  is delimited on all sides by a solid wall. Beyond the cyclone inlet, the airflow passing along the duct  178  is physically unrestrained, at least in part. In the embodiment shown, the cyclone inlet is generally parallel to the uppermost portion of the side wall  174   a  of the barrier member  170  defining the flowpath  142   a  which leads to the respective cyclone inlet. The duct  178  is shaped and configured so as to force the airflow passing therealong to enter the cyclone  104  in a helical manner in order to effect cyclonic separation therein. The duct  178  can be arranged so as to effect a tangential entry to the cyclone  104  or, as been mentioned above, can also be arranged to effect a scroll entry. 
   The cyclone inlet need not be circular in shape. Indeed, in the embodiment illustrated, the cyclone inlet is roughly U-shaped. However, it is possible to calculate an effective radius of the cyclone inlet by taking the actual cross-sectional area and assuming that it is in fact circular in shape. Hence, using the formula area=π×radius 2 , the effective radius of the cyclone inlet can be calculated. In the embodiment shown, the actual area of the cyclone inlet is 180 mm 2 , which gives an effective radius of 7.57 mm. The length of the flowpath  142   a , measured from the point in the passageway  142  at which the airflow is divided to the cyclone inlet, is at least five times the effective radius of the cyclone inlet. It is preferred that the length of the flowpath  142   a  is at least seven times the effective radius of the cyclone inlet. In the embodiment shown, the length of the flowpath  142   a  is approximately 68 mm, which is approximately 9 times the effective radius of the cyclone inlet. 
   The relative dimensions described above allow the decrease in cross-sectional area of the flowpath  142   a  to be gradual and the rate of decrease to be substantially constant. The result is that the airflow passing along the flowpath  142   a  increases in velocity without suffering excessively high losses in the process. 
   In the embodiment, the cross-sectional area of each of the flowpaths  142   a , measured at the point in the passageway  142  at which the airflow is divided, is approximately 985 mm 2 . If the cross-sectional area of the cyclone inlet is 180 mm 2 , then this represents a reduction in cross-sectional area of approximately 80%. In other embodiments which are not illustrated here, the decrease can be somewhat less than 80%, 70% and 60% being acceptable reductions in area. Hence, the cross-sectional area of the cyclone inlet can be between 60% and 80% of the area of the flowpath  142   a  at the point in the passageway  142  at which the airflow is divided. 
   As previously mentioned, the longitudinal axis  148  of each downstream cyclone  104  is inclined towards the longitudinal axis  150  of the downstream cyclone unit  103 . The upper end of each downstream cyclone  104  is closer to the longitudinal axis  150  than the lower end thereof. In this embodiment, the angle of inclination of the relevant axes  148  is substantially 7.5°. 
   The upper ends of the downstream cyclones  104  project inside the collection moulding  120 , as previously mentioned. The interior of the collection moulding  120  defines a chamber  152  with which the upper ends of the downstream cyclones  104  communicate. The collection moulding  120  and the surfaces of the downstream cyclones  104  together define an axially extending passageway  154 , located between the downstream cyclones  104 , which communicates with the collection space  134  defined by the internal wall  132 . It is thus possible for dirt and dust which exits the smaller ends of the downstream cyclones  104  to pass from the chamber  152  to the collection space  134  via the passageway  154 . 
   Each downstream cyclone  104  has an air exit in the form of a vortex finder  156 . Each vortex finder  156  is located centrally of the larger end of the respective downstream cyclone  104 , as is the norm. In this embodiment, a centre body  158  is located in each vortex finder  156 . Each vortex finder communicates with an annular chamber  160  which, in turn, communicates with the outlet port  126 . 
   The mode of operation of the apparatus described above is as follows. Dirty air (being air in which dirt and dust is entrained) enters the cyclonic separating apparatus  100  via the inlet port  114 . The arrangement of the inlet port  114  is essentially tangential to the wall of the cylindrical bin  106  which causes the incoming air to follow a helical path around the inside of the cylindrical bin  106 . Larger dirt and dust particles, along with fluff and other large debris, are deposited in the collection space  138  adjacent the base  108  by virtue of the effect of centrifugal forces acting on the particles, as is well known. Partially cleaned air travels inwardly and upwardly away from the base  108 , exiting the upstream cyclone  102  via the perforated portion  144  of the shroud  140  and passing into the air passageway  142 . 
   Once inside the passageway  142 , the partially cleaned air moves upwardly parallel to the axis  150  and is divided into seven airflow portions as it passes the sharp edges  176  at the lowermost points of the barrier members  170 . Each individual airflow portion then passes along the respective flowpath  142   a . In doing so, the cross-sectional area airflow portion is reduced by virtue of the fact that the cross-sectional area of the respective flowpath  142   a  is reduced. The rate of decrease is governed by the shape and configuration of the barrier members  170  and, in the case of the embodiment shown in the drawings, the rate of decrease is substantially constant, at least whilst the airflow portion flows along the majority of the length of the flowpath  142   a.    
   Depending upon the shape and configuration of the flowpath  142   a , the airflow portion decreases in cross-sectional area by at least 60% between the time at which it enters the flowpath  142   a  and the cyclone inlet. In the embodiment shown, the percentage reduction in cross-sectional area is approximately 80%. This ensures that the airflow portion is traveling at a relatively high velocity as it exits the flowpath  142   a  and enters the respective cyclone  104 . 
   Each airflow portion enters one of the downstream cyclones  104  via the respective inlet  146 . As has been mentioned above, each inlet  146  is a scroll inlet which forces the incoming air to follow a helical path inside the downstream cyclone  104 . The tapering shape of the downstream cyclone  104  causes further, intense cyclonic separation to take place inside the downstream cyclone  104  so that very fine dirt and dust particles are separated from the main airflow. The dirt and dust particles exit the uppermost end of the respective downstream cyclone  104  whilst the cleaned air returns to the lower end of the downstream cyclone  104  along the axis  148  thereof and exits via the vortex finder  156 . The cleaned air passes from the vortex finder  156  into the annular chamber  162  and from there to the outlet port  126 . Meanwhile, the dirt and dust which has been separated from the airflow in the downstream cyclone  104  falls from the chamber  152  through the passage-way  154  to the collection space  134 . 
   When it is desired to empty the cyclonic separating apparatus  100 , the base  108  can be hingedly released from the sidewall of the cylindrical bin  106  so that the dirt and debris collected in collection spaces  134  and  138  can be allowed to drop into an appropriate receptacle. As previously explained, the detailed operation of the emptying mechanism does not form part of the present invention and will not be described any further here. 
   It will be appreciated that the invention need not be confined to the precise details of the embodiment described above. Various alterations and variations may be made without departing from the scope of the invention. For example, the number of downstream cyclones  104  shown in the embodiment is seven. However, there is no particular limit to the number of downstream cyclones which can be provided, or indeed to their arrangement with respect to one another or to the upstream cyclone. The downstream cyclones can thus be varied in number and arrangement. Also, the precise manner in which the airflow is divided within the passageway is not critical, although the reduction of the cross-sectional area of each flowpath is necessary in order to achieve the aims of the invention. It is envisaged that the invention may have applications in field other than the vacuum cleaner industry.