Abstract:
A bleed valve for introducing bled fluid to a mainstream fluid flowing through apparatus across which a pressure differential occurs, characterized in that the bleed valve is adapted to open so as to bleed fluid into the mainstream fluid when the pressure differential across the apparatus falls below a predetermined value. This arrangement is particularly appropriate to vacuum cleaners incorporating cyclonic dust-separating apparatus in that the bleed valve is more reliably operated in response to a reduction in airflow. This ensures efficient functioning of the cyclonic dust-separating apparatus and reduces the risk of overheating of the motor.

Description:
This application is a division of U.S. patent application Ser. No. 09/214,732, filed Jun. 11, 1999, now U.S. Pat, No, 6,231,649, which is a 371 of PCT/GB97/01802 filed Jul. 3, 1997. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to apparatus for separating particles from a fluid flow particularly, but not exclusively, to apparatus for separating dust from an airflow in a vacuum cleaner. The invention also relates to a valve for introducing bled fluid to a mainstream fluid. 
     BACKGROUND OF THE INVENTION 
     Separation apparatus incorporating at least one bleed valve is known, for example from published International patent application Ser. No. PCT/GB93/01325. In that arrangement, a bleed valve is arranged upstream of a cyclonic separator such that, if the pressure (which is normally directly related to the airflow) in the separator falls below a predetermined level, air is bled into the airflow path from the atmosphere in order to maintain a minimum airflow. This allows the cyclonic separator to operate satisfactorily and ensures that the motor is effectively cooled. Whilst this known arrangement is perfectly adequate in most cases, it has been found that there are some instances when its performance could be improved. For example, a vacuum cleaner will normally include a filter, separate from the main dust-separating apparatus, located either immediately upstream or downstream of the motor. If this filter becomes clogged, the airflow through the dust-separating apparatus (i.e. the cyclonic separator) will be reduced and this can prevent sufficient suction being developed in the dust-separating apparatus to cause the bleed valve to bleed air into the dust-separating apparatus. The result can be reduced effectiveness or efficiency of the cyclonic separator and, more importantly, an increased risk of the motor overheating. 
     It is also known from UK patent No. 1080504 to provide a signal device for a vacuum cleaner which operates in response to an increase in pressure differential across the bag or filter to indicate that the filter requires changing. The signal is given by bleeding air along a conduit and across a reed to give an audible indication that the filter should be changed. 
     It is an object of the present invention to provide a bleed valve which is not dependent upon absolute pressures in order to operate. 
     It is also an object of the present invention to provide improved apparatus for separating particles from a fluid flow, particularly suitable for use in a vacuum cleaner, which is capable of reliably bleeding air into the separation apparatus so as to maintain a minimum airflow therein and to reduce the risk of the motor overheating. 
     A further object of the invention is to provide improved apparatus for separating particles from a fluid flow, particularly suitable for use in a vacuum cleaner, which can be utilised to indicate that a blockage is present. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a bleed valve. The invention also provides an apparatus containing a bleed valve. 
     The present invention further provides a valve for introducing a fluid between an inlet and outlet of an apparatus, which comprises: a valve head which is movable between an open and a closed position to open and close a first opening into the valve; a housing means having: (i) a first section, defining the first opening leading to a first chamber on one side of a flexible seal means mounted between the housing means and the valve head of the piston means to be connected by a second opening in the first section upstream of flow of the fluid in the apparatus; (ii) a second section defining a second chamber on an opposite side of the seal means and between the piston means and the second section, with a third opening in the second section to be connected downstream of a fluid flow in the apparatus; and bias means mounted so as to hold the piston means with the valve head in the open position at rest and wherein when a first flow of fluid through the apparatus includes a pressure in the second section less than the pressure in the first section, the valve head is in the closed position in the opening and the fluid is prevented from flowing through the opening in the valve and wherein when a blockage of fluid flow occurs between the inlet and the outlet of the apparatus the valve is in the open position while the fluid is flowing to admit fluid into the valve and apparatus. 
     The present invention also provides an apparatus having a fluid air flow between an inlet and an outlet through an element which produces a pressure drop and which is subject to becoming blocked, by means of a valve which allows fluid to be introduced between the inlet and the outlet, the improvement wherein the valve comprises a valve head which is movable between an open and a closed position to open and close a first opening into the valve in response; a housing means having: (i) a first section, defining the first opening leading to a first chamber on one side of a flexible seal means mounted between the housing means and the valve head of the piston means connected by a second opening in the first section upstream of flow of fluid in the apparatus; (ii) a second section defining a second chamber on an opposite side of the seal means and between the piston means and the second section, with a third opening in the second section connected downstream of a fluid flow in the apparatus; and bias means mounted so as to hold the piston means with the valve head in the open position at rest and wherein when a first flow of fluid through the apparatus includes a pressure in the second section less than the pressure in the first section, the valve head is in the closed position in the opening and the fluid is prevented from flowing through the opening in the valve and wherein when a blockage of fluid flow occurs between the inlet and the outlet of the apparatus, the valve is in the open position while the fluid is flowing to admit fluid into the valve and apparatus. 
     The provision of a bleed valve which is responsive to a drop in the pressure differential measured across the separation apparatus means that ambient fluid is bled more reliably into the flow path. This is because the pressure drop across the separation apparatus, particularly cyclonic separation apparatus, is directly related to the flow rate. The pressure losses are due primarily to friction which is highly dependent upon the flow rate. The higher the flow rate, the greater the pressure drop across the cyclonic separation apparatus. 
     It is important to maintain an adequate flow rate through separation apparatus, particularly cyclonic separation apparatus, if good separation is to be maintained. It is also very important to maintain an adequate flow of cooling air or other fluid past a motor in order to avoid overheating. The present invention therefore represents a significant improvement over the prior art. 
     Since a drop in the pressure differential (i.e. flow rate) across the separation apparatus is indicative of a blockage in the flow path, the operation of the bleed valve can also be used to indicate that a blockage is present and provide a signal to the user that maintenance is required. In the prior art arrangements, a blockage located between the separation apparatus and the fan or motor can fail to cause the bleed valve to operate. 
     A further advantage of the present invention is that the bleed valve will normally be open when the motor is switched off. In the prior art arrangement, the bleed valve would be shut and may not open if a blockage is present at the time the motor is switched on. In the apparatus according to the invention, the bleed valve stays open until a sufficient pressure drop is achieved across the dust-separating apparatus. This ensures that the motor is adequately cooled at all times. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described with reference to the accompanying drawings wherein: 
     FIGS. 1 and 1A are schematic illustrations of cyclonic vacuum cleaners according to the prior art mentioned in the introduction hereto; 
     FIG. 2 and 2A are schematic illustrations similar to FIGS. 1 and 1A illustrating the invention; 
     FIG. 3 is an enlarged front cross-sectional view of an embodiment of the bleed valve forming part of the vacuum cleaner illustrated schematically in FIGS. 2 and 2A; 
     FIG. 3A is an exploded perspective view of the bleed valve shown in FIG. 3; 
     FIG. 4 is a view similar to FIG. 3 of an alternative embodiment of the bleed valve forming part of the vacuum cleaner illustrated schematically in FIGS. 2 and 2A; 
     FIG. 4A is a plan view of the valve of FIG. 4 shown in situ; and 
     FIG. 4B is an exploded perspective view of the valve of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 1A are schematic illustrations of known vacuum cleaners. In each case, the vacuum cleaner  10  incorporates a nozzle  12  attached directly to a hose  14  and the hose  14  is directly connected to dust-separating apparatus  16 . The dust-separating apparatus  16  can be any conventional dust-separating apparatus, such as a bag filter, but in this case comprises cyclonic separating apparatus consisting of two cyclones  16 A,  16 B arranged in series. The arrangement, dimensions and operation of such dust-separating apparatus  16  are well documented elsewhere and will not be described any further here, other than to mention that a bleed valve  18  is located in the airflow path either upstream of the cyclones  16 A,  16 B (FIG. 1) or between the two cyclones  16 A, 16 B (FIG.  1 A). Downstream of the dust-separating apparatus  16  is a pre-motor filter  20 , followed by a fan  22 , a motor  24  and a post-motor filter  26 , seen in the direction of airflow. The operation of cyclonic separating apparatus of this type is described in U.S. Pat. Nos. 4,571,772; 4,593,429; 4,643,748; 4,826,515; 4,853,008; 4,853,011; 5,062,870; 5,078,761; 5,090,976; 5,145,499 and 5,160,356 but does not form part of the present invention. 
     In use, the motor  24  operates to activate the fan  22  which causes a flow of air to pass from the nozzle  12  to the dust-separating apparatus  16  via the hose  14 . After separation has taken place, the airflow passes through the pre-motor filter  20 , past the fan  22 , past the motor  24  providing a cooling effect, and through the post-motor filter  26  before being expelled to the atmosphere. The bleed valve  18  is arranged such that, if the pressure within the dust-separating apparatus  16 , and particularly at the location within the dust-separating apparatus  16  at which the bleed valve  18  is placed, drops below a pre-determined value, the bleed valve  18  opens so as to allow air from the atmosphere to enter the cyclonic dust-separating apparatus in order to maintain an adequate airflow to effect separation. The prevention of the airflow from falling below a predetermined level also ensures that the motor  24  is adequately cooled so as to prevent any risk of overheating. 
     If either of the filters  20 , 26  becomes sufficiently clogged to cause a reduction in the airflow within the vacuum cleaner  10 , the airflow through the dust-separating apparatus  16  is reduced. However, because the blockage is located downstream of the dust-separating apparatus, the flow rate in the dust-separating apparatus  16  is reduced but the pressure drop across the apparatus  16  is small. All the pressure drop occurs across the blocked filter. This prevents the bleed valve  18  from operating. In these circumstances, the prior art bleed valve  18  does not provide adequate protection against overheating of the motor  24 . 
     FIGS. 2 and 2A illustrate the same type of vacuum cleaner as illustrated in FIGS. 1 and 1A but with the bleed valve  18  replaced by a bleed valve  30  in accordance with the invention. All other parts of the schematically illustrated cleaners are provided with reference numerals identical to those shown in FIGS. 1 and 1A. 
     The bleed valve  30  consists essentially of a piston  32  housed within a chamber  34 . A first side of the piston  32  is connected via a line  36  to a point in the airflow path immediately upstream of the entire dust-separating apparatus  16  (FIG. 2) or alternatively to a point in the airflow path immediately upstream of the downstream cyclone  16 B (FIG.  2 A). The other side of the piston  32  is directly connected via line  38  to a point in the airflow path immediately downstream of the dust-separating apparatus  16 . Thus, any pressure differential existing across the entire dust-separating apparatus  16  (FIG. 2) or across the downstream cyclone  1   6 B (FIG. 2A) is applied directly across the piston  32 . 
     Resilient biasing means  40  are applied to the piston  32  so that, when a predetermined pressure differential is applied across the piston  32 , the piston  32  is in fact in equilibrium. When the pressure differential drops below the predetermined value, the piston  32  moves under the action of the biasing means  40  so as to open a vent  42  which, when open, will allow atmospheric air to enter the airflow path of the vacuum cleaner  10  at a point upstream of the dust-separating apparatus  16 . The introduction of this bled air has the same effect as the air bled into the airflow path by the bleed valve  18  shown in FIGS.  1  and IA but is dependent upon the pressure differential across the dust-separating apparatus  16  or the downstream cyclone  16 B rather than upon the absolute pressure therein. 
     FIGS. 3 and 3A illustrate a bleed valve  50  suitable for use in the arrangements illustrated in FIGS. 2 and 2A. The bleed valve  50  essentially comprises a housing  52 ,  76 A,  76 B and a piston  54 . The housing  52  defines two ports  56 ,  58  to which lines can be connected for suitable connection to the airflow path upstream and downstream respectively of the dust-separating apparatus  16  or the downstream cyclone  16 B. The housing  52  also defines a chamber  60  in which the piston  54  is slidably mounted. The housing  52  also comprises a central portion  62  for receiving and supporting the biasing means and a supporting central rod. 
     More specifically, the housing  52  is generally annular in shape. The central portion  62  is generally cup-shaped and has a central aperture  64  to allow a rod  66  to pass slidingly therethrough. Apertures  68  and/or a central aperture  70  are provided in the central portion  62  in the vicinity of the aperture  64 . The function of these apertures  68 ,  70  will be described later. 
     Radially outwardly of the central portion  62  is a flange portion  72  designed to receive one end of a diaphragm seal  74 , the other end of which will be fixedly attached to the piston  54 . The flange  72  also defines part of the chamber  60 , the remainder of which is defined by a radially-outwardly extending wall  76  of the housing  52 . The outermost edge of the housing  52  is shaped so as to close the chamber  60 , to define the port  58  and to receive the other side of the diaphragm seal  74 . The port  56  is arranged in the housing  52  displaced in an axial direction with respect to the port  58 . The side of the port  56  remote from the port  58  defines an axial, annular aperture  56 A which can be closed by the head portion of the piston  54  which will be described later. A flexible seal  78  is located around the periphery of this aperture to facilitate airtight sealing and is held in place by upper wall  76 A and cleaner wall  76 B. 
     The piston  54  has a main body  80  and a head portion  82 . The main body  80  is generally dish-shaped and the radially-outer portions are shaped so as to slide easily within the chamber  60 . Sufficient play is provided between the radially-outer portions  84  and the chamber  60  to allow the rolling diaphragm  74  to operate therebetween. The radially-outer portions of the piston  54  are manufactured in two separate portions in order to allow the diaphragm seal  74  to be securely trapped between the separate portions so as to provide an adequate working seal. 
     The central portion of the piston  54  has a central aperture  86  for receiving the rod  66 . The rod  66  is fixedly retained in the central portion of the piston  54  and a bolt  88  located at the end of the rod  66  is provided to hold the head  82  of the piston  54  on the rod  66 . Some play is allowed between the rod  66  and the head  82  in order to allow sufficient leeway to accommodate some misalignment between the rod  66  and the remainder of the bleed valve  50 . 
     A spring  90  is positioned between the housing  52  and piston  54 . The spring  90  abuts against the housing  52  between the flange  72  and the central portion  62 . The spring  90  also abuts against the central portion of the piston  54  adjacent the aperture  86  for receiving the rod  66 . The rod  66  carries a stop  92  on its end remote from the bolt  88 . This stop  92  limits the movement of the rod  66  in an axial direction. 
     The bleed valve  50  described above can have any appropriate dimensions. However, tests have shown that a bleed valve  50  having a head portion  82  with a diameter of around 26 mm and a piston  54  with an outer diameter of around 49 mm operates effectively. Other dimensions will be selectable around these dimensions to suit particular applications and to achieve a compact design. It is preferred that the rod  66  is allowed to move axially by at least 4 mm. 
     The bleed valve  50  is illustrated in a closed position. The outer edges of the head  82  are pressed against the seal  78  so that the unit as a whole is closed. Port  56  is connected to the airflow path of the vacuum cleaner immediately upstream of the dust-separating apparatus  16  or the downstream cyclone  16 B and therefore the upstream pressure acts directly on the surface of the piston  54  which is shown to the left in FIG.  3 . The port  58  is connected to the airflow path immediately downstream of the dust-separating apparatus  16  and therefore the downstream pressure acts directly on the downstream side of the piston  54  illustrated on the right in FIG.  3 . Atmospheric pressure acts on the left hand side of the bead  82  as illustrated and on the right hand side of the center of the piston  54  by virtue of the fact that the area in which the spring  90  is placed is open to atmosphere by way of the apertures  68 ,  70 . 
     As long as the pressure differential across the dust-separating apparatus  16  or the downstream cyclone  16 B remains sufficiently large, the piston  54  is pressed to the right against the action of the spring  90 . However, as soon as the pressure differential drops below a predetermined minimum, the action of the spring  90  takes precedence over the pressure differential acting across the piston  54  and the piston  54  will move to the left. The head  82  therefore also moves to the left and the seal between the head  82  and the seal  78  is broken. Therefore, atmospheric air can enter the bleed valve between the head  82  and the seal  78  and atmospheric air will then pass through the port  56  and enter the airflow path upstream of the dust-separating apparatus  16  or downstream cyclone  16 B. The airflow within the cyclones is thereby maintained and sufficient airflow is provided to cool the motor. 
     As soon as the pressure differential across the dust-separating apparatus  16  or downstream cyclone  16 B returns to an acceptable level, the piston  54  will move again to the right and the head  82  will re-seal the opening. Atmospheric air will again be excluded from the airflow passing through the dust-separating apparatus  16 . The apertures  68 ,  70  are provided with dimensions which will ensure that the movement of the piston  54  is naturally damped by the egress of air from the area between the housing and the piston. 
     A preferred feature of the invention is the provision of indication means operated by the movement of the piston  54  which will warn the user of the apparatus that maintenance is required. This can be easily achieved by providing a switch  94  operable by the movement of the piston  66  for activating a warning light  96  or other signalling means. In order to avoid unnecessary warnings being given, the indication means can be arranged so as to provide a warning only when the bleed valve  50  is operated repeatedly or for a prolonged period. Means for achieving this are well known in the art. 
     FIGS. 4,  4 A and  4 B show an alternative bleed valve  100  with a head portion  102  in an open position with an airflow as shown by the arrows and as more fully described hereinafter for use in the apparatus of FIGS. 2 and 2A. The bleed valve  100  includes a housing  104  with a piston  124  held in place. The housing  104  includes ports  108  which are in airflow connection to a cyclone exhaust port  202  defined by walls  204  of the cleaner  200 . The port  202  is thus in a downstream position. Second ports  110  are provided in the valve  100  which are in airflow connection to an upstream chamber  206  of the cleaner  200  defined by walls  208  and tubular extensions  210  which support and seal the bleed valve  100  in position. Air flows in a spiral manner into chamber  212  through chambers  214  and through a port  216  which forms an inlet into the inner cyclone  16 B shown in FIG. 2A so as to be between the inner cyclone  16 B and outer cyclone  16 A. Walls  204  and  218  define chamber  212 . Walls  218  and  207  define chamber  214 . 
     The housing  104  of valve  100  defines a chamber  112  in which the piston  124  moves. A central portion  114  of the housing  104  supports a post or rod  116 . The central portion  114  of the housing  104  is provided with a recess  118  which receives a seal retainer  120  for mounting a coil spring  122 . Piston  124  includes the head portion  102  which is mounted on the main body of the piston  124  by means of a cap  126 . The piston  124  is generally dish-shaped and extends toward the exhaust port  202 . Seal  128  is mounted on the piston  124  and the housing  104  so as to provide a seal between the exhaust port  202  and a chamber  132  between the main body of the piston  124  and an upper portion  134  of the housing  104 . Flow director vanes  136  are provided adjacent the head portion  102  of the valve  100  to keep the airflow from tending to close the valve  100 . These are angled towards the ports  110 . 
     The seal  128  is mounted at one side in a recess  138  in the housing  104  and is held in place by seal retainer  120 . In the middle of the seal  128 , a ring retainer  140  holds the seal  128  in position on the piston  124  by means of snaps  142 . At the other side of the seal  128 , the upper portions  134  and the housing  104  hold the seal in position in a recess  144 . A recess  146  is also provided on the main body for the seal  128 . Seal  148  is provided between tubular extensions  210  and the upper portion  134  of the piston  106 . The valve  100  is held in place by retaining screws in openings  150  (FIG. 4A,  4 B). FIG. 4 also shows the wall  218  of the outlet port  202  which returns to an opening  222  (FIG. 4A,  4 B) adjacent the valve  100  and seal  220 . 
     In operation, the head portion  102  of the piston  124  is open as shown in FIG. 4, when the cleaner motor  24  is not operating. In the normal air flow operating condition of the valve  100  when the motor is operating, the valve is closed. If a blockage occurs in the cleaner, thus restricting airflow, the valve  100  opens due to the reduced pressure differential between chambers  112  and  132 , which allows the spring  122  to bias the piston  124  and head portion  102  into the open position shown in FIG.  4 . The valve  100  is maintained in this position until the blockage is removed. 
     As shown in FIG. 4B, an indicator needle  300  is secured to a helix  301  and slidably mounted in retainer  106  on rod  116 . As the head portion  102  moves on rod  116 , a pin (not shown) in retainer  106  causes the needle  300  to rotate. This indicates the position of the valve. 
     The invention is not limited to the specific embodiments described above. Fundamentally, it is envisaged that the bleed valve could be incorporated into apparatus for separating particles from a flow of gas other than air or, possibly, a liquid. The apparatus has applications outside the vacuum cleaner industry and therefore the invention should not be regarded as limited to that industry. The bleed valve itself could also be applied across other apparatus and is therefore usable in other areas. Various alternative arrangements and other variations will be apparent to a reader skilled in the art.