FILTERS

Abstract: A filter which may be incorporated in a vacuum cleaner, comprises a store for filter-web in the form of a roll (11), pulling means comprising a driven endless belt (40) and a cooperating plate (43) of a resiliently deformable material (or two rollers) arranged to draw web from inside the roll in the form of a spiral tube which passes between the belt and the plate (or the two rollers), particulate laden fluid being directed to the inside of the roll and outwardly through it so that particulate matter is trapped within the tube as web is drawn from the roll, the tube containing such matter being conveyed by the pulling means (40, 43) to a used filter-web store (26).

Description: FILTERS This invention concerns filters of a kind comprising means defining a flow path for fluid which is connected or connectible to means for propelling a flow of fluid along the flow path, and means for locating a porous filter material in the flow path so that fluid flowing along the flow path flows through the material and any particulate matter entrained in the flow of fluid is removed from the flow as the fluid flows through the material . Such filters are extremely common for filtering liquids and gases, e.g. paper filters for filtering liquids in laboratories to collect precipitates, air filters for removing dust and pollen. In some cases, sustained filtering of fluids heavily laden with solid particulates is needed, for collection of the particulate matter for subsequent treatment or disposal, and the build-up of particulate matter gives rise to high resistance to the flow. Such high resistance can be problematical in, for example, filters in suction cleaners (commonly referred to as "vacuum cleaners") causing loss of suction and overheating of the motor (which drives an impeller for propelling air through the filter) as the filter becomes clogged with particulate matter . One way of overcoming these problems is disclosed in our co-pending Application No. GB 2323775, the whole content of which is incorporated hereinto by reference. This Application discloses a suction cleaner comprising a motor to drive an impeller in a housing to propel a flow of air along a flow path within the housing via filter means in the housing, which is characterised in that the filter means comprises a feed filter-web store, filter web advance means to draw filter-web from the store to expose fresh portions of the web to the flow path, and a used filter-web store in the housing to receive used filter-web and deposits thereon. In the used filter-web store the bulk of the matter collected is separate from the filter-web, and can give rise to problems during disposal. Furthermore, the filter means disclosed is not well suited to other uses, and problems arise in trying to adapt it e.g. for filtering liquids . In order to reduce or avoid such problems, the present invention provides a filter comprising means defining a flow path for fluid which is connected or connectible to means for propelling a flow of fluid along the flow path, and means for locating a porous filter material in the flow path so that fluid flowing along the flow path flows through the material and any particulate matter entrained in the flow of fluid is removed from the flow as the fluid flows through the material, characterised in that:- (a) the filter is provided with a store for a filter-web in the form of a roll, filter web advance means to draw filter-web from a roll in the store to expose fresh portions of the web to the flow path, and to convey used portions of the web to a used filter-web store which thereby receives used filter-web and particular matter deposited thereon; (b) the filter-web advance means comprises traction or pulling means arranged to draw web from the store in the form of a spiral tube; (c) the flow path is arranged so that, in use, particulate laden fluid is directed to the inside of the roll and flows outwardly through the roll, so that as the web is drawn from the store in the form of a tube particulate matter is trapped within the tube and conveyed to the used filter-web store wrapped in the tube. The used filter-web store may have a drain opening over, or be disposed alongside, a sump so that a suction cleaner incorporating the filter can be used as a "wet and dry" cleaner if the filter web is insoluble in, and resistant to degradation by, liquids. The wrapped particulate matter can be easily and conveniently removed for disposal, simply by tearing the tube where it emerges from the pulling means. The traction or pulling means is preferably of automatic form, but may be manually actuated. The automatic form of said means preferably comprises a mechanism responsive to pressure differential between inlet and outlet portions of the air flow, i.e. the pressure differential across the portion of the web. The filter-web used in the filter of the invention is preferably a roll of fibrous sheet material or porous paper which is relatively inexpensive. The invention will be described further, by way of example, with reference to the accompanying drawings in which: - FIGURES 1A and IB show diagrammatically a filter web and pulling means of a filter of the invention, respectively in cross-section and in elevation; FIGURE 2 shows the internal arrangement of a suction cleaner having a filter in accordance with one embodiment of the invention; FIGURE 3 shows, similarly, the internal arrangement of a second embodiment; FIGURE 4 is a similar view of a third embodiment; and FIGURE 5 is a similar view of a fourth embodiment Referring to FIGURES 1A and IB the filter 10 uses a roll 11 of filter-web 12 of a porous paper or fibrous sheet material, from the inside surface of which roll 11 the web 12 is withdrawn linearly, in the direction of arrow A by pulling means 27, with the result that it naturally forms a spirally wound tube 13 in which the turns overlap by at least 1cm and preferably two or more centimetres . In use, if suction is applied to the periphery of the roll 11 and fluid with particulate matter entrained therein is directed into the open end 14 of the roll, the fluid will pass through the roll leaving the particulate matter behind on the exposed inside surface of the roll. As the exposed or clogged web 12 is withdrawn from within the roll it will carry the particulate matter away with it and expose fresh portions of web material from the next successive internal turns 12A, B, et seq, of the roll, so as to reduce the flow resistance of the filter, the particulate matter being wrapped in the tube 13, which becomes flattened by the pulling means 27. Referring to FIGURES 2, 3, 4 and 5, the filter 10 of each of the embodiments shown therein is incorporated into a suction cleaner 20. The roll 11 is fitted into a perforate sleeve 21 between annular sealing discs 22 and 23. The sleeve 21 is located in an outer housing 24, and extends from one end of an inner housing 25 within which a used filter-web store 26 is provided at the other end. The tube 13 is conveyed into the store 26 by automatically operable pulling means 27. The outer housing 24 has an inlet end piece 32 which defines an inlet opening 33 and abuts the sealing disc 22 to clamp the latter against one end 34 of the roll 11 and against the adjacent ends of the housings 24 and 25; and the housing 25 is provided with an internal funnel shaped guide 35 to guide the tube 13 towards the pulling means 27. The guide 35 abuts the sealing disc 23. An extractor fan and motor unit 36 is provided to draw air from a flow space 37 between the housings 24 and 25, thereby to generate a flow of air into the inlet 33 and through the filter 10 for removal of particulate matter from the air flow. Subsequently, the collected particulate matter, enclosed in the tube 13, is compressed as it passes through the pulling means 27 prior to entering the store 26. In the embodiments shown in FIGURES 2 and 3 the pulling means 27 comprises an endless belt 40 which runs around two reversing rollers 41,42, and a plate 43 arranged so that the filter-web tube 13 passes between it and one run of the belt 40, the plate being resiliently biased so as to press the tube against the belt and to permit any large pieces of material picked up by the cleaner to pass between the plate and the belt into the store 26. The roller 41 is a drive roller driven by an electric motor 44 and the roller 42 is an idler roller. The belt is made of rubber or other suitable material and its outer surface is formed with serrations or ribs so that it can exert an effective pulling force on the tube 13. An automatic differential-pressure sensitive actuating means 45 is provided to control energisation of the motor 44. In the embodiment of FIGURE 2 the plate 43 is made of a resiliently deformable, low friction plastics material, for example polypropylene, and is of generally inverted U-shape, one limb being attached to a mounting 46 on inner housing 25 and the other limb acting, in use, to press the tube 13 against the belt 40. As a low friction material is used for the plate 43 the tube 13 easily slips over it . The second embodiment shown in FIGURE 3 differs from the first embodiment shown in FIGURE 2, in that the plate 43 which may be made of a similar material, is of curved form and is urged by a differential pressure thrust device 47 towards the belt 40 with a force which varies with the difference between atmospheric pressure and the pressure inside the housing 25. The device 47 comprises a chamber 48 which is defined by a bellows 49, is open at one side to atmosphere through a duct 50 and is closed at the other side by a diaphragm 51, the plate 43 being attached to an arm 52 projecting from this diaphragm so that movement of the diaphragm caused by variations in the pressure difference varies the pressure applied by the plate to the tube 13. In use, in both embodiments, the actuating means 45 responds to an increase to a predetermined level in the difference between the pressure in the housing 25 and the pressure in the flow space 37 caused by particulate matter deposited on the exposed inside surface of the roll 11 creating resistance to the flow of fluid through the roll, to switch on the motor 44, and responds when said difference falls below said level caused by a fresh portion of the roll being exposed inside the roll to switch the motor 44 off again. Thus, said difference varies with the flow resistance of the filter. In the first embodiment the rate at which the tube 13 is pulled through the pulling means 27 can be varied by variation of the pressure applied by the plate 43 to the tube. Taken to one extreme, said rate could be entirely dependant upon said thrust so that the motor 44 can run continuously, thus obviating the actuating means 45. In the event of the filter roll 11 becoming exhausted, the sleeve 21 will become exposed and the pressure in the flow space 37 will rise suddenly. This rise may be employed to actuate a pressure sensitive limit switch (not shown) to switch off the motor 44, but it is preferred to provide a window ( not shown ) in the housing 25 so that the user can visually inspect the state of the filter 10 and the store 26. In the embodiments of FIGURES 4 and 5 the pulling means 27 comprises a drive roller 28 driven by a motor 29, a pressure roller 30 to compress the tube 13 against the drive roller 28, and automatic differential-pressure sensitive actuating means 31 which operates in the same way as the actuating means 45 to control energisation of the motor 29. The fourth embodiment shown in FIGURE 5 differs from the third embodiment shown in FIGURE 4, in that the pressure roller 30 is urged by a differential pressure thrust device 38 towards the roller 28 with a force which increases with the difference between atmospheric pressure and the pressure inside the housing 25. This thrust device 38 is of the same construction and operates in the same way as the thrust device 47 of the second embodiment. In the fourth embodiment, the rate at which the tube 13 is pulled through the pulling means can be varied by varying the thrust applied to the pressure roller 30. Taken to one extreme, said rate could be entirely dependant upon said thrust so that the motor 29 can run continuously, thus obviating the actuating means 31. For use in a suction or vacuum cleaner as disclosed in said co-pending Application, the location of the suction motor and the flow path may be re-arranged so that the motor discharges air near to the inlet 33 thereby enabling the inlet and outlet return flows to be connected to the cleaning nozzle. The present invention further provides a filter or filter apparatus or a suction cleaner having any novel part or feature or novel combination of functional parts or features disclosed herein or in the accompanying drawings, and functional equivalents thereof.

Claims: CLAIMS 1. A filter comprising means (24,25) defining a flow path for fluid which is connected or connectible to means for propelling a flow of fluid along the flow path, and means (22,23) for locating a porous filter material in the flow path so that fluid flowing along the flow path flows through the material and any particulate matter entrained in the flow of fluid is removed from the flow as the fluid flows through the material, characterised in that:- (a) the filter is provided with a store for a filter-web in the form of a roll (11), filter-web advance means (27) to draw filter web from a roll in the store to expose fresh portions of the web to the flow path, and to convey used portions of the web to a used filter-web store (26) which thereby receives used filter-web and particulate matter deposited thereon; (b) the filter-web advance means comprises traction or pulling means (26) arranged to draw web from the store in the form of a spiral tube ( 13 ) ; (c) the flow path is arranged so that, in use, particulate laden fluid is directed to the inside of the roll (11) and flows outwardly through the roll, so that as the web is drawn from the store in the form of a tube particulate matter is trapped within the tube and conveyed to the used filter-web store (26) wrapped in the tube. 2. A filter as claimed in Claim 1 in which the traction or pulling means (27) comprises a driven roller (28,41) arranged to act on the tube ( 13 ) to draw web from the web store. 3. A filter as claimed in Claim 2 in which the driven roller ( 41 ) is arranged to drive an endless belt ( 41 ) which is arranged to engage the tube, the tube being pressed against the belt by resiliently deformable means (43). 4. A filter as claimed in Claim 3 in which the resiliently deformable means comprises a plate ( 43 ) formed so that the tube slips over it. 5. A filter as claimed in Claim 4 in which the plate (43) is made of a resiliently deformable material. 6. A filter as claimed in Claim 2 in which the driven roller ( 28 ) is arranged to contact the tube ( 13 ) which is pressed against the roller by a further roller (30). 7. A filter as claimed in Claim 4, 5 or 6 in which the plate ( 43 ) or further roller ( 30 ) is operatively connected to a differential pressure thrust device (38,47) operable to vary the pressure with which the plate or roller is applied to the tube ( 13 ) in accordance with variations in the difference between atmospheric pressure and fluid pressure inside the flow path. 8. A filter as claimed in Claim 4, 5, 6 or 7 in which the driven roller is driven by an electric motor controlled by actuating means (31,41) operable to energise the motor and cause web to be drawn from the roll (11) when the difference between atmospheric pressure and the fluid pressure in the flow path reaches a predetermined level . 9. A filter as claimed in any one of the preceding claims in which a guide (35) is provided to guide the web from the roll (11) towards the filter web advance means (27). 10. A filter substantially as herein described with reference to FIGURES 1A and IB or FIGURE 2, 3, 4 or 5 of the accompanying drawings.

Inventors: CARVER LEONARD JOHN, WRIGHT ALAN THOMAS, CARVER, LEONARD, JOHN, WRIGHT, ALAN, THOMAS
Applicants: CARVER LEONARD JOHN, CARVER PLC, WRIGHT ALAN THOMAS, CARVER, LEONARD, JOHN, WRIGHT, ALAN, THOMAS
Application year: 1998
Main classification: A47L9
IPC codes: A47L9, B01D46