A fluid filtering unit

Abstract: The fluid filtering unit comprises a filter element 20 through which fluid being filtered must pass and means for cleaning the filter element in situ without interruption of the filtering process. The cleaning means comprises a collector 24 movable between a first position and a second position relative to the filter element on the upstream side of the filter element during a cleaning operation, means for urging the collector at least in use towards its first position relative to the filter element, means for moving the collector from its first position to its second position relative to the filter element against the force of the urging means, and means 30, 42 for automatically connecting the collector to dump at a pressure less than that of the fluid being filtered as the collector moves from its first position relative to the filter element towards its second position relative to the filter element.

Description: This invention relates to a fluid filtering unit comprising an arrangement for cleaning the filter by backflushing. It is known from AT-B-377709, US-A-3994810 and AT-B-392217 to provide fluid filtering units including an arrangement for cleaning the filter by back flushing. AT-B-377 709 teaches a fluid filtering unit comprising a reciprocating back-flush unit for cleaning the filter, in which the back-flush unit is motor driven in both directions of operation of the back-flush unit. The contaminants and fluid flushed out of the filter are passed to a dump through an independent valve assembly. US-A-3 994 810 describes a similar arrangement for motorized actuation of the back-flush unit in both directions of operation. AT-B-392 217 teaches a back-flush unit using an external hydraulic/pneumatic cylinder to activate the back-flush unit in both directions. According to the present invention there is provided a fluid filtering unit comprising a filter element through which fluid being filtered must pass and means for cleaning the filter element in situ without interruption of the filtering process, the cleaning means comprising a collector movable between a first position and a second position relative to the filter element on the upstream side of the filter element during a cleaning operation, means for urging the collector towards its first position relative to the filter element, means for moving the collector from its first position to its second position relative to the filter element against the force of the urging means, and means for automatically connecting the collector to dump at a pressure less than that of the fluid being filtered as the collector moves from its first position relative to the filter element towards its second position relative to the filter element so that filtered fluid on the downstream side of the filter element will pass to dump via the filter element and the collector to force contaminants collected by the upstream side of the filter element into the collector and to progressively clean the filter element as the collector moves relative to the filter element, wherein the collector is capable of being urged towards its first position relative to the filter element either by differential pressure created by the fluid being filtered, acting on the collector, or by a spring. Preferably, the collector is capable of being moved from its first position to its second position by means operated by fluid pressure sourced externally of the filter unit. Conveniently, the collector is in the form of a piston slidable along the upstream side of the filter element. In this case, the piston may have an annular groove adjacent to the filter element, at least one radial passage capable of communicating the groove to dump and at least one axial passage providing communication between opposite sides of the piston. Preferably, the means for automatically connecting the collector to dump comprises valve means having a first valve part fixed relative to the collector and a second valve part fixed relative to a housing containing the filter element. Preferably, the filter element is mounted on the downstream side of an apertured, cylindrical filter support and the collector is movable relative to the filter support in close proximity to the filter support during a cleaning operation. In this case, preferably, the apertures in the filter support have a diameter (or equivalent dimension) less than one width of lands on opposite sides of the annular groove in the piston so that flow of unfiltered fluid to dump is choked. Preferably, the collector and filter element are so arranged that the entire surface area of the filter element can be cleaned during a cleaning operation. The invention will now be more particularly described, by way of example, with references to the accompanying drawings, in which:- Figure 1 is a longitudinal section taken through one embodiment of a fluid filtering unit according to the invention; Figure 2 is a side view of the filtering unit shown in Figure 1; and Figure 3 is a section taken along line III - III of Figure 2. Referring to the drawings, the fluid filtering unit shown therein comprises a housing 10 having an inlet port 11, an outlet port 12, and a pilot port 13. The housing 10 also has a blind, stepped chamber 14 accommodating three removable parts 15, 16 and 17 which are fixed in position relative to the housing 10. The part 15 has in its outer peripheral surface an annular groove 18 which communicates with the outlet port 12 in the housing 10. The base of the groove 18 defines the outer surface of a cylindrical filter support 19. A filter element 20 of wedge wire construction is wound or otherwise mounted on the outer surface of the support 19 and the support 19 has a plurality of radial apertures 21 therein which are arranged in annular spaced apart rows. As an alternative, the filter element 20 could be of flat weave construction mounted on the support 19 to give it collapse strength and having an apertured cylinder against its outer surface to provide burst strength. The part 16 has in its outer peripheral surface an annular groove 22 which communicates with the inlet port 11 in the housing 10 and the part 16 also has passages 23 which provide fluid communication between the groove 22 and the interior of the part 15. The part 17 defines a return passage 45 which is, in use, connected to drain. The fluid filtering unit also comprises a collector 24 movable within the part 15. The collector 24 comprises a piston 25 movable relative to the filter support 19 in close proximity to the upstream side of the filter support 19 during a cleaning operation and an integral piston rod 26 slidably supported at one end by an end portion 27 of the part 15 and at the other end by the part 16. A seal 28 is provided between the end portion 27 of the part 15 and the piston rod 26. Two spaced apart seals 29 and 30 are provided between the piston rod 26 and the part 16. Seals 31 and 32 are provided between the part 15 and the housing 10. A seal 33 is provided between the parts 16 and 17. A seal 34 is provided between the part 17 and the housing 10. The piston 25 has an annular groove 35 defined between two annular lands 36 and 37 which are a fairly close fit (but not a sealing fit) within the part 15. The piston also has at least one, and typically four, radial passages 38 which communicate the annular groove 35 with an axial passage 39 formed in the piston rod 26. The piston 25 also has at least one, and typically eight, axially extending passages (not shown) disposed between adjacent pairs of radial passages 38 providing communication between opposite sides of the piston 25. The left hand end of the axial passage 39 (as viewed in Figure 1) in the piston rod 26 is closed by a plug 41 and a plurality of radially extending apertures 42 are provided in the piston rod 26 at the right hand end thereof and communicate with the passage 39. When the piston 25 is in its extreme left hand position (as shown in Figure 1), fluid in the passage 39 is prevented from flowing to drain via the return passage 45 in the part 17 by the seal 30. However, when the piston 25 is moved to the right (as viewed in Figure 1) to bring the apertures 42 to the right of the seal 30, the passage 39 communicates with drain via the return passage 45 in the part 17. The left hand end of the chamber 14 communicates with the pilot port 13 via a restrictor 46 and, in use, the pilot port 13 is connected selectively to drain or fluid under pressure by an external solenoid operated valve 43. When the pilot port 13 is connected to drain, a pressure differential across the collector 24 (resulting from the different diameters of seals 28 and 29) keeps the piston 25 in its extreme left hand position. Fluid entering the housing 10 via the inlet port 11 will pass into the part 15 via the groove 22 and passages 23 in the part 16, and will be filtered by the filter element 20 before leaving the housing 10 via the outlet port 12. When the pilot port 13 is connected to fluid under pressure, the piston 25 is moved to the right and, as soon as the axial passage 39 in the piston rod 26 communicates with the return passage 45 in the part 17 (i.e. when the apertures 42 move to the right of the seal 30), high pressure filtered fluid on the downstream side of the filter element 20 forces contaminants collected on the upstream side of the filter element 20 into the piston 25 and to drain. The piston 25 will sweep the entire surface area of the filter element 20 to progressively clean the filter element 20 and will come to a rest when the piston rod 26 makes contact with a radially inwardly projecting shoulder 44 on the part 17. The speed at which the piston 25 sweeps past the filter element 20 is controlled by the restrictor 46. The piston 25 then remains at its extreme right hand position until the valve 43 is operated to again connect the pilot port 13 to drain. When this happens, the pressure at the pilot end of the chamber 14 will decay slowly through the restrictor 46 and the pressure differential across the collector 24 (resulting from the different diameters of seals 28 and 29) will return the piston 25 to its extreme left hand position. During this return movement of the piston 25, high pressure filtered fluid on the downstream side of the filter element 20 will again force any remaining contaminants collected on the upstream side of the filter element into the piston and to drain. As the piston 25 approaches its extreme left hand position the axial passage 39 in the piston rod 26 will be cut off from the return passage 45 to prevent any further flow of filtered fluid to drain. Filtering of fluid will continue during the cleaning operation. The width of the lands 36 and 37 on either side of the annular groove 35 in the piston 25 is greater than the diameter of the apertures 21 in the filter support 19 to choke flow of unfiltered fluid to drain via the collector 24 as the piston 25 traverses the filter support 19. The solenoid operated valve 43 could be operated by a computer or by a sensor (not shown) responsive to the degree of contamination of the filter element 20. It could also be replaced by a manually operable valve. Return movement of the piston to its extreme left hand end could be effected by the urging force of a spring instead of by differential pressure across the collector.

Claims: A fluid filtering unit comprising a filter element (20) through which fluid being filtered must pass and means for cleaning the filter element in situ without interruption of the filtering process, the cleaning means comprising a collector (24) movable between a first position and a second position relative to the filter element on the upstream side of the filter element during a cleaning operation, means for urging the collector towards its first position relative to the filter element, means for moving the collector from its first position to its second position relative to the filter element against the force of the urging means, and means (30,42) for automatically connecting the collector to dump at a pressure less than that of the fluid being filtered as the collector moves from its first position relative to the filter element towards its second position relative to the filter element so that filtered fluid on the downstream side of the filter element will pass to dump via the filter element and the collector to force contaminants collected by the upstream side of the filter element into the collector and to progressively clean the filter element as the collector moves relative to the filter element and wherein the collector (24) is capable of being urged towards its first position relative to the filter element (20) either by differential pressure created by the fluid being filtered acting on the collector, or by a spring. A fluid filtering unit as claimed in Claim 1, wherein the collector (24) is capable of being moved from its first position to its second position by means operated by fluid pressure sourced externally of the filter unit. A fluid filtering unit as claimed in any one of the preceding claims, wherein the collector is in the form of a piston (25) slidable along the upstream side of the filter element. A fluid filtering unit as claimed in Claim 3, wherein the piston (25) has an annular groove (35) adjacent to the filter element, at least one radial passage (38) capable of communicating the groove to dump and at least one axial passage providing communication between opposite sides of the piston. A fluid filtering unit as claimed in any one of the preceding claims, wherein the means for automatically connecting the collector to dump comprises valve means having a first valve part (42) fixed relative to the collector and a second valve part (30) fixed relative to a housing containing the filter element. A fluid filtering unit as claimed in any one of the preceding claims, wherein the filter element is mounted on the downstream side of an apertured, cylindrical filter support (19) and the collector is movable relative to the filter support in close proximity to the filter support during a cleaning operation. A fluid filtering unit as claimed in Claim 6, when dependant on Claim 4, wherein the apertures (21) in the filter support have a diameter (or equivalent dimension) less than the width of lands (36,37) on opposite sides of the annular groove in the piston so that flow of unfiltered fluid to dump is choked. A fluid filtering unit as claimed in any one of the preceding claims, wherein the collector (24) and filter element (20) are so arranged that the entire surface area of the filter element can be cleaned during a cleaning operation.

Inventors: ELLIOTT-MOORE PETER, OZIEM CHRISTOPHER, ELLIOTT-MOORE, PETER, OZIEM, CHRISTOPHER
Applicants: LONGWALL ROOF SUPPORTS LTD, LONGWALL ROOF SUPPORTS LIMITED
Application year: 1995
Main classification: B01D29
IPC codes: B01D29