Abstract:
A vacuum cleaner ( 1 ) comprises an inlet ( 13 ), an outlet, a fan ( 14 ) for creating a flow of air through the vacuum cleaner ( 1 ) by drawing air to be cleaned through the inlet ( 13 ) into the vacuum cleaner ( 1 ) and by exhausting air through the outlet outwardly of the vacuum cleaner ( 1 ) and a separator ( 15, 41 ). The separator ( 15, 41 ) is rotatably arranged around an rotation axis ( 21 ), for creating, during use, a column of rotating air to separate at least a portion of the airborne particles ( 10 ) from the flow of air. The separator ( 15, 41 ) includes a number of vanes ( 25, 44 ) for the creation of the column of rotating air, wherein each vane ( 25, 44 ) is provided with a leading face ( 26 ) and a trailing face ( 27 ). The leading faces ( 26 ) of the vanes ( 25, 44 ) are inclined with respect to the rotation axis ( 21 ) for conveying the airborne particles ( 10 ) at least in an axial direction.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a vacuum cleaner, comprising 
         [0000]    an inlet for receiving, during use, air to be cleaned, the air to be cleaned being laden with airborne particles,
 
an outlet for expelling air outwardly of the vacuum cleaner,
 
a fan for creating a flow of air through the vacuum cleaner by drawing the air to be cleaned through the inlet into the vacuum cleaner and by exhausting air through the outlet outwardly of the vacuum cleaner and
 
a separator rotatably arranged around an rotation axis, for creating, during use, a column of rotating air to separate at least a portion of the airborne particles from the flow of air, which separator includes a number of vanes for the creation of the column of rotating air, wherein each vane is provided with a leading face and a trailing face.
 
       BACKGROUND OF THE INVENTION 
       [0002]    Such a vacuum cleaner is known from U.S. 2004/0068826 A1. By the vacuum cleaner disclosed in U.S. 2004/0068826 A1 air with airborne particulates and water droplets are being moved from the air inlet opening to the separator. The separator includes a cup shaped body having a bottom and a wall, further defined by a plurality of vanes extending upwardly from the bottom to an open top. The vanes comprise a curved flow surface for increased particulate separation and reductions in aerodynamic losses. The vanes extend longitudinally with respect to a body and are generally tapered radially relative to a rotation axis of the separator like an air foil. The curved flow surface extends along the length of each of the vanes. The separator comprises vanes to force the air and the airborne particulates to rotate about the rotation axis of the separator. Due to centrifugal forces the airborne particulates will be moved away from the vanes. The longitudinally extending vanes define a plurality of longitudinal gaps or openings, formed there between. Fluid and particulates are drawn into the exterior of the separator via the gaps. As the particulates are drawn in, the separator, which is being rotated at a relatively high angular velocity, applies a centrifugal force to the particulates and to the air and water. The particulates are forced outwardly of the separator body where they can be expelled back into a water bath. Cleaned air is then exhausted from the separator through an outlet. 
         [0003]    EP 1219223 A2 discloses a liquid-assisted suction cleaner with a separator rotating at high speed, of a truncated-cone shaped structure formed of a number of radial helical vanes, slightly concave externally, whose width and thickness decrease from a thick ring, forming the greater base, to the smaller base with a flat bottom, said vanes being held firm by an internal ring, said separator being preferably constructed in one single piece of plastic material, balanced by adjustment, in the die used to mould it, of the depth of cavities made in the thick ring and in the bottom, a coat of epoxy paint being applied inside and outside to prevent formation of humid areas that would lead to variations in dimensions that in turn would be the cause of vibrations. 
         [0004]    EP 0890335 A1 discloses separator unit for liquid bath vacuum cleaners used for separating from the introduced air the particles of dirt and/or dust sucked with drops of water, the separator unit comprising at least a hollow body shaped like a truncated cone assembled on the drive shaft of the intake assembly of the vacuum cleaner, the hollow body including laterally a plurality of longitudinal slits to discharge the introduced particles of dirt/dust and/or drops of liquid, the separator unit comprising a disk-shaped supporting element axially holed and keyed onto the drive shaft, the supporting element being coupled with the hollow body by means of a peripheral edge with a tooth to couple with the upper edge of the hollow body, the supporting element including a plurality of radial apertures for the passage of the ingested air and a plurality of discharge slits made radially on the portion of the peripheral edge which defines the tooth. 
         [0005]    U.S. 2004/098958 A1 discloses a separator for a wet vacuum cleaner has a bottom and a sidewall connected to the bottom. The sidewall has lamellas delimiting slots, wherein through the slots an air/gas flow enters an interior of the separator, delimited by the bottom and the sidewall, wherein the air/gas flow contains dirt/dust particles and/or water droplets. The lamellas each have at least one radial outer widened section, extending in a rotational direction of the separator, and at least one remaining lamella section, wherein the at least one radial outer widened section and the at least one remaining lamella section delimit together a turbulence chamber, respectively. In view of today&#39;s requirements in the field of sustainability there is a call for low-energy or energy-saving devices. As a result of this there is a continuous ambition to improve on the energy consumption of domestic appliances such as vacuum cleaners. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the invention to provide a vacuum cleaner of the above mentioned kind having improved separation efficiency. 
         [0007]    This object is achieved by the vacuum cleaner according to the invention in that the leading faces of the vanes are inclined with respect to the rotation axis for conveying the airborne particles at least in an axial direction to a zone of a reduced proportion between drag forces versus centrifugal forces. 
         [0008]    Before exhausting the air to the outside of the vacuum cleaner again, the flow of air is subjected to the action of the separator to separate as much as possible the airborne particles or particulates in the flow of air from the air in order to clean the air. The air having a low specific mass is dragged into the separator by the vacuum generated by the turbine or fan. The airborne particles are also dragged towards the separator along with the air into which they are airborne. In the vicinity of the separator the airborne particles enter into a column of rotating air caused by the high-speed rotation of the separator. On top of the drag forces which convey the particles towards the separator and into the column of rotating air, the airborne particles are being subjected to centrifugal forces due to the action of the column of rotating air. Hence, in the column of rotating air the airborne particles are on the one hand subjected to centrifugal forces which tend to expel the particles away from the separator and on the other hand subjected to drag forces which tend to take the airborne particles into and through the separator. There is a balance between the drag forces and the centrifugal forces by virtue of which the separation process works and specifically its efficiency is determined. 
         [0009]    If the drag forces on an airborne particle outweigh the centrifugal forces on said particle, the particle enters the separator, thereby harming the overall separation efficiency. Vice versa, if the centrifugal forces outweigh the drag forces the airborne particle is thrown out of the column of rotating air without flowing through the separator, thereby resulting to a successful separation and to an increase of the separation efficiency. 
         [0010]    The separator is equipped with a number of vanes which convey the air when it enters the separator. If a trajectory of an air molecule flowing into the separator, i.e. a flow line, is considered, a distinction can be made between the so-called leading face and trailing face of the vane. This leads to a side or part of the vane that first approaches the air flowing along a flow line when the separator is rotating; this side is referred to as the leading face of the vane. As the air continues its path around the vane it will subsequently reach the other side of the vane which is referred to as the trailing face of the vane. The leading face of a vane is the edge or side of the vane which faces the air that flows towards the separator and the vane; the trailing face of a vane is the rearmost edge or side of the moving vane as seen in the direction of the airflow. A direction which is parallel to the rotation axis of the separator is referred to as “axial direction”. 
         [0011]    As explained above the balance between drag forces and centrifugal forces on the airborne particles lays down the separation efficiency. In axial direction, this balance between the drag and centrifugal forces generally varies. For example, the separator may have a proximal side which is close to the fan and a distal side which is remote from the fan. In such a configuration a possible flow pattern which emanates from the fan and separator is known as a so-called flow sink. In such a flow sink the drag forces close to the fan are relatively high compared to the drag forces at the distal end of the fan, whereas the centrifugal forces show less variation in axial direction. In the context of such a flow sink an important phenomenon is that the velocities of air volumes which are close to the fan are relatively high compared to the velocities of air volumes which are at a relatively large distance from the fan. As a consequence the drag forces are relatively high close to the fan compared with the drag forces at a larger distance from the fan. The magnitude of drag forces approximately scale with the reciprocal value of the squared air velocity. Hence in a zone of reduced proportion of drag forces versus the centrifugal forces, the balance between drag forces and centrifugal forces is in favor of the centrifugal forces, which is advantageous for the separation efficiency. With this result of improved separation efficiency in mind the invention recognizes that it is advantageous to guide the airborne particles to a zone of a reduced proportion between the drag forces versus the centrifugal forces. This is accomplished by the vacuum cleaner according to the invention in that the leading face is at an inclination to force the air and the particles thereon in axial direction, parallel to the direction of the rotation axis, preferably to a zone of reduced drag forces in relation to the centrifugal forces where the drag forces are more easily defeated by the centrifugal forces on said particles. In this manner also relatively small and light particles can be separated from the flow of air. The improved separation efficiency may be realized without increase of the rotational speed of the separator. 
         [0012]    A separator may be formed from a rigid material such as glass filled polystyrene material, and the like, and may be injection moulded. Normally a draft angle is imposed on a moulded component of the separator to provide ability to release the moulded component from its mould. This draft angle is created by decreasing the thickness of the vanes in axial direction. The thickness of a vane is the distance between a first point on the leading face and a second point on the trailing face of the vane, the first and second point being positioned at the same radial distance from the rotation axis. The draft angle is determined by a difference of the inclination between the leading face and the trailing face. Such a draft angle is not sufficient to create the envisaged effect of conveying or forcing the airborne particles in axial direction. Contrary thereto, the inclination of the leading face which is required to force the particles into the axial direction and which is required to significantly increase the separation efficiency according to the invention exceeds the value of the draft angle. Alternatively, the tangent of the angle of inclination of the leading face is larger than the ratio between the material thickness and the length of the vane in axial direction to obtain the envisaged separation efficiency. 
         [0013]    The statement “the leading faces of the vanes are inclined” does not exclude the existence of non-inclined point(s) at the leading faces of the vanes, and therefore refers to “at least portions of the leading faces of the vanes are inclined”. 
         [0014]    In an embodiment of the vacuum cleaner according to the invention, the leading face has a first portion and a second portion, wherein the first portion is inclined in a positive direction and the second portion is oppositely inclined in a negative direction, said positive and negative directions being opposite directions, for guiding airborne particles at least in corresponding opposite axial directions. 
         [0015]    The purpose of forcing the particles in axial direction is to convey the airborne particles to a zone of a favorable ration between drag and centrifugal forces, i.e. a zone of improved separation efficiency. By providing a first and a second portion, each inclined in different directions, the flow of air which approaches the leading face will either be split and directed towards two efficient zones or be concentrated and directed to one efficient zone. This shortens the length of path in axial direction that the airborne particles have to abridge to arrive in an efficient separation zone. If the efficient zone is axially near the middle of the vane, the airborne particles should be forced towards the middle. If the efficient zones are axially near the ends of the vanes, the flow should be split up and conveyed towards the efficient zones near the ends of the blades. 
         [0016]    In a very advantageous embodiment of the vacuum cleaner according to the invention, the fan is coaxially arranged with the separator, each vane having a proximal and a distal end, the proximal ends being between the fan and the distal ends, wherein the leading faces are inclined with respect to the rotation axis in a direction for guiding airborne particles towards the distal ends. 
         [0017]    Axially away from the fan the ratio between drag forces and the centrifugal forces is significantly smaller than axially close to the fan. By the inclination of the leading faces a counter airflow is generated that helps to prevent airborne particles such as dust and dirt from penetrating through the separator end entering, dirtying or even damaging other vacuum cleaner compartments and components. 
         [0018]    In another embodiment of the vacuum cleaner according to the invention, the separator comprises at least one plate extending perpendicular to the rotation axis, the vanes being arranged on at least one side of the plate, wherein the leading faces of the vanes are inclined for conveying the airborne particles in axial direction towards the plate. 
         [0019]    At such a plate additional forces on top of the drag and centrifugal forces will be exerted to the air by the surface of the air. Thus the surface of the plate and the boundary layer of air which is close to the surface will provide an extra pumping effect or pumping force which counteracts the drag forces and helps the centrifugal forces emanating from the column of rotating air. Air will stick to the surface of the plate. The combination of centrifugal forces and pumping forces, i.e. the forces caused by the extra pumping effect, can more easily outweigh the drag forces than the centrifugal forces alone so that the airborne particles will be thrown out of the column of rotating air more effectively resulting to an even more successful separation. Since the plate has two sides, vanes can be arranged on both sides, the pumping effect can be provided for both the vanes which are axially above the plate and for the vanes which are axially below the plate. Thereto the inclinations of the vanes above the plate may be such as to force the airborne particles down towards the top surface of the plate and the inclinations of the vanes below the plate may be such as to force the airborne particles upwards to the bottom surface of the plate. 
         [0020]    In a further embodiment of the vacuum cleaner according to the invention the separator comprises two plates extending perpendicular to the rotation axis, which plates are connected to opposite axial ends of the vanes, wherein the opposite axial directions extend towards the opposite axial ends. 
         [0021]    With such an embodiment, near each axial end of each vane relatively small particles can easily be moved away from the separator. The two plates and the vanes there between form a composition of a segment. If two or more of such segments are axially built together a segmented separator is obtained with a corresponding multitude of zones of increased separation efficiency. In such a segmented set-up of the separator the axial length of the flow paths, i.e. the lengths of the paths which is needed to bring the particles to a zone of improved separation efficiency, can be considerably reduced. 
         [0022]    In yet another embodiment of the vacuum cleaner according to the invention the plate has a radius, which radius is larger than the maximum distance between of a tip of the vanes and the rotation axis. 
         [0023]    During rotation of the separator, an air flow will be created over the plate which counteracts the airflow into the separator and will cause a force extending away from the rotation axis, which force will be supplementary to the centrifugal forces. The larger the plate is, the larger the force extending away from the rotation axis will be. 
         [0024]    In another embodiment of the vacuum cleaner according to the invention, at least in one plane perpendicular to the rotation axis, each vane is curved from an inner edge to an outer edge in a direction opposite to the direction of rotation, wherein the inner edge is located closer to the rotation axis than the outer edge. 
         [0025]    Due to the so curved vanes, particles on the front side of the vanes will be forced by the vanes away from the rotation axis. 
         [0026]    In another embodiment of the vacuum cleaner according to the invention, the vanes have a portion which is helically arranged. 
         [0027]    Such vanes can easily be produced because the angle at which the leading faces are inclined with respect to the rotation axis is constant along the length of the vane in axial direction, i.e. the axial length of the vane. 
         [0028]    In another embodiment of the vacuum cleaner according to the invention, the inclined vane has an angle with respect to the rotation axis, which angle varies along the length of the vane in the axial direction into which the airborne particles are being forced by the inclined vanes. 
         [0029]    By applying a varying inclination angle the tendency of airborne particles to move in axial direction can be adapted to their axial position at which they approach the separator. Particles which are already near a separation efficient zone do not need as much axial displacement as particles which are relatively far away from the separation efficient zones. Hence by applying a varying inclination angle the overall separation efficiency may be tuned and further improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The invention will be explained in more detail with reference to the drawings, in which 
           [0031]      FIG. 1  is a schematic cross section of a vacuum device according to the invention, 
           [0032]      FIG. 2  is a schematic perspective view of a separator of the vacuum device as shown in  FIG. 1 , 
           [0033]      FIG. 3  is an enlarged side view of a part of the separator as shown in  FIG. 2 , 
           [0034]      FIGS. 4A and 4B  are enlarged bottom views of a part of the separator as shown in  FIG. 2 , 
           [0035]      FIG. 5  is an enlarged side view of a part of a separator of another embodiment of the vacuum device according to the invention. 
           [0036]      FIG. 6  is a schematic representation of a vane. 
       
    
    
       [0037]    Like parts are indicated by the same reference numbers in the figures. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0038]    In  FIG. 6  a cross-section of a vane  25  of a separator  15  is schematically depicted. The vane  25  is rotating in a clockwise direction around an axis of rotation  21  of the separator  15 . The direction of rotation is indicated by a curved arrow R. A practical embodiment of the separator  15  is in general equipped with a number of such vanes; however, in  FIG. 6  only one vane is depicted. If a trajectory  32  of an air molecule flowing into the separator, i.e. a flow line, is considered, a distinction can be made between a so-called leading face  26  and trailing face  27  of the vane  25 . This leads to a side or part of the vane that first approaches the air flowing along flow line  32  when the separator is rotating; this side is referred to as the leading face of the vane. As the air continues its path around the vane it will subsequently reach the other side of the vane which is referred to as the trailing face  27  of the vane. The leading face  26  of a vane is the side of the vane which faces the air that flows towards the separator and the vane; the trailing face  27  of a vane is the rearmost side of the moving vane as seen in the direction of the airflow. 
         [0039]      FIG. 1  shows a vacuum cleaner  1  comprising a housing  2  in which two brushes  3 ,  4  are rotatably mounted around axles  5 ,  6 . The brushes  3 ,  4  are driven by a motor (not shown). The brush  3  is rotatable in a clockwise direction, indicated by arrow P 3  and the brush  4  is rotatable in a counter clockwise direction, indicated by arrow P 4  around the respective horizontal axles  5 ,  6 . The brushes  3 ,  4  are fully enclosed except at the bottom by the housing  2 . The housing  2  is provided with wheels (not shown) keeping the axles  5 ,  6  at a predetermined distance of the surface to be cleaned. The housing  2  is provided with a handle  7  at a side remote of the brushes  3 ,  4 . Between the handle  7  and the brushes  3 ,  4  the vacuum cleaner  1  is provided with a reservoir  8  for a cleansing fluid like water and a debris collecting container  9  for fluid and particles  10  picked up from the surface  11  to be cleaned. The debris collecting container  9  is provided with a hollow tube  12  extending from an air inlet opening  13  between the brushes  3 ,  4  into the debris collecting container  9 . At a side of the debris collecting container  9  opposite the tube  12  there is provided a vacuum fan  14  and a rotatable separator  15 . 
         [0040]    In use, the vacuum cleaner  1  is being moved in a direction as indicated by arrow P 1  over the surface to be cleaned  11 . During said movement, the brushes  3 ,  4  are being rotated in the opposite directions P 3 , P 4  directed towards each other near the surface to be cleaned  11 . Cleansing fluid from the reservoir  8  is applied via the brush  3  on the surface  11 . By moving the brushes  3 ,  4  over the surface to be cleaned  11  particles like dirt and other materials are being disconnected from the surface  11 . Simultaneously, the surface  11  is being cleaned by the cleansing fluid. By further moving the vacuum cleaner  1  in the direction as indicated by arrow P 1 , the disconnected particles  10  and the cleansing fluid on the surface are being moved upwards into the air inlet opening  13  due to the rotational movement of the brushes  3 ,  4 , i.e. the fluid and particles  10  picked up from the surface  11  to be cleaned will become airborne. Furthermore, the air with the airborne particles  10  and cleansing fluid is being moved from the air inlet opening  13  into the tube  12  towards the debris collecting container  9  by means of the vacuum fan  14 . In the debris collecting container  9  most of the particles will fall directly downwards towards the bottom of the debris collecting container  9  into dirty fluid  16  that has already been picked up or that was already present in the container  9 . Instead of falling directly to the bottom of the container  9  there are also particles that tend to move towards the vacuum fan  14 . These particles that tend to move upwards to the fan  14  are prevented there from by the separator  15  which acts counterproductive to the vacuum fan  14 . The relatively heavy particles will be moved away from the separator  15  and will fall downwards into the dirty fluid  16 . The relatively light air will pass the separator  15  and be moved through the vacuum fan  14  and the cleaned air will leave the vacuum cleaner via an air outlet opening. 
         [0041]      FIGS. 2-4B  show different views of the separator  15  being rotatable about a rotation axis  21 . The separator  15  comprises two round plates  22 ,  23  having different diameters. The central axis of the plates  22 ,  23  forms the rotation axis  21 . The plate  22  is of a smaller diameter than plate  23  and is provided with a centrally located hole  24 . This plate  22  is located closer to the vacuum fan  14  than the plate  23 . The plates  22 ,  23  are located at a distance of each other and are connected to each other by means of vanes  25 . Each vane  25  has a leading face  26  and a trailing face  27  seen in the rotation direction R ( FIGS. 2 ,  4 A,  4 B). As can be seen in  FIG. 3 , the vanes  25  are inclined with respect to the rotation axis  21  and the leading face  26  encloses an angle A with the plate  23 . Each vane  25  is curved from an inner edge  28  to an outer edge  29  in a direction opposite to the rotation direction R, wherein the inner edge  28  is located closer to the rotation axis  21  than the outer edge  29 . Between the vanes  25  passages  30  are present through which air will flow from the debris collecting container  9  towards the vacuum fan  14  in a direction as shown by arrow P  1  ( FIG. 2 ). 
         [0042]    When rotating the separator  15  about the rotation axis  21  in the rotation direction R, a column of rotating air will be created by the high-speed rotation of the separator  15 . The air having a low specific mass compared to the dirt and particles which are airborne therein is dragged into the separator  15  by drag forces caused by the vacuum generated by the vacuum fan  14 . The airborne particles are also dragged towards the separator  15  along with the air into which they are airborne. In the vicinity of the separator  15  the airborne particles enter into the column of rotating air. On top of the drag forces which convey the particles towards the separator  15  and into the column of rotating air, the airborne particles are being subjected to centrifugal forces due to the action of the column of rotating air. 
         [0043]    In  FIG. 4B , a relative velocity profile v air  of air and airborne particles in the passage  30  between a trailing face  27  of one vane  25  and the leading face  26  of another vane  25  is indicated relative to the vane  25 . As will be appreciated by the skilled person this velocity is relative to the trailing face because the vanes are rotating at high angular velocity. As can be seen, the velocity at the leading face  26  is much smaller than at the trailing face  27 . 
         [0044]    In  FIGS. 4A and 4B  a trajectory  32  of an air molecule  31  flowing into the separator  15  is shown. After being lead to the leading face  26 , the air molecule  31  will flow around the outer edge  29  towards the trailing face  27 . It will then flow through the passage  30  and through the hole  24  ( FIG. 2 ) towards the vacuum fan  14 . A heavier airborne particle  10  will be subjected to the drag forces and the centrifugal forces. If the centrifugal forces outweigh the drag forces the airborne particle  10  is thrown out of the column of rotating air without flowing through the separator  15 . The heavier particle  10  will follow the trajectory  32  towards the leading face  26  and away there from. 
         [0045]    Due to the curvature of the vanes  25  from the inner edge  28  to the outer edge  29  in a direction opposite to the rotation direction R, the leading faces  26  will also exert a pushing force on the particles  10  in a direction away from the rotation axis  21 . A vane having this effect is known as a so-called non-catching vane. 
         [0046]    As can be seen in  FIG. 3 , the particles  10  will be directed by the inclined leading faces  26  of the vanes  25  in axial direction towards the plate  23  which is located further away from the vacuum fan  14  than the plate  22 . Near the plate  23  the drag forces are lower than near the plate  22 . Furthermore, the rotating plate  23  with the larger diameter will create a pumping effect on the air near the plate  23  in a direction away from the rotation axis  21 . Due to the pumping effect, a pumping force will be exerted on the air and the airborne particles  10 . This pumping effect counteracts the drag forces and helps the centrifugal forces emanating from the column of rotating air. Near the plate  23  the combination of centrifugal forces and pumping forces can easily outweigh the drag forces, so that also relatively light airborne particles will be thrown out of the column of rotating air down to the dirty water in the container  9  resulting into a successful separation. 
         [0047]      FIG. 5  shows a side view of a separator  41  of another embodiment of a vacuum cleaner according to the invention. The separator  41  comprises two plates  42 ,  43  and vanes  44  extending between the plates  42  and  43 . Both plates  42  and  43  have a radius larger than the radius of the vanes  44 . The vanes  44  are curved in a plane perpendicular to the rotation axis to provide the non-catching effect as described above according to a previous embodiment. The vanes  44  are also curved in a plane parallel to the rotation axis, as can be seen in  FIG. 5 . The curvature in the plane parallel to the rotation axis is such that the leading face  45  has a first portion  46  and a second portion  47 , which are inclined in a positive direction and a negative direction respectively. Said positive and negative directions are opposite directions. Particles  10  are guided by either the first portion or the second portion of the leading face  45  of the vane  44  in opposite axial directions towards the plates  42 ,  43 . 
         [0048]    It is also possible to use plates which have a shape other than round. However, given the fact that the separator has to provide separation at high angular velocities the plates should preferably not introduce too much unbalance. 
         [0049]    It is also possible to provide a number of separators  15  on top of each other wherein the centrally located hole  24  extends through all the plates except the plate directed towards the debris collecting container  9  to prevent air and airborne particles to directly enter hole  24 . 
         [0050]    Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the words like “comprising” and “having” do not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.