FILTER ASSEMBLIES The invention relates to filter assemblies.
One form of known filter assembly comprises a filter element contained within a housing. The housing comprises an inlet for feeding fluid to be filtered to the filter element and an outlet for removing filtered fluid. In the course of such filtration, the filter element becomes progressively more blocked with material removed from the fluid until the filter element must be changed. To do this, the housing is opened and the filter element removed, disposed of and replaced.
This can be a messy job because there will be residual fluid within the housing and material removed by the filter element may flow from the filter element as it is taken out of the housing. As well as being messy, such removal can be dangerous where the fluid being filtered presents a health hazard.
There have been various proposals for overcoming this problem. In US-A-3344925, the housing is lined with a liner whose upper edges can be lifted and folded round the filter element to lift the filter element from the housing. GB-A-2176126 connects the filter element to an adapter and then provides a thin sleeve of film-like material surrounding the element. EP-A-0555740 is similar to US-A-3344925 in providing a bag within the housing that can be drawn up to enclose the filter element after the lid has been detached. US 3684100 has the element in a shell of thin plastic material closed at one end and open at the other end.
According to a first aspect of the invention, there is provided a filter assembly comprising a filter element, casing surrounding the element, the casing being formed by a head member providing an inlet and an outlet, with the filter element being mounted on said head member, and a self supporting bowl connected to the head member and receiving the filter element, and a housing containing the casing.
By"self-supporting"is meant that the bowl will support itself and maintain its shape at room temperatures when not in use.
It can also be a problem in known filter assemblies of this kind where the filter element has an open centre. This is, after use, filled with a volume of fluid that must be disposed of with the filter element.
According to a second aspect of the invention, there is provided a filter assembly comprising a housing containing a filter element and having an inlet for fluid to be filtered by the filter element and an outlet for filtered fluid, the filter element having an open centre through which fluid flows in the path thereof between the inlet and the outlet, the centre containing a member that reduces the volume of the core. A further problem with known filter assemblies of this kind is of passing fluid to and from interior and exterior surfaces of the filter element.
According to a third aspect of the invention, there is provided a filter assembly comprising a housing containing a tubular filter element with a hollow centre, an interior surface and an exterior surface, a head member providing an end cap for an end of the filter element and also providing a first passage leading to the centre of the filter element and a second passage leading to the exterior surface of the filter element.
In known filter assemblies of this kind, cost is a significant factor. It is desirable to keep the number of parts to a minimum.
According to a fourth aspect of the invention, there is provided a filter element comprising a tubular filter member having a first end and a second end, the first end being closed by a head member providing a first passage and a second passage and the second end being closed by an end cap, the head member including a part which is substantially the same as the end cap and has a hole leading to the first passage.
The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings in which : - Figure 1 is a schematic cross-section, partly broken away, of a first filter assembly showing a housing, a casing and a filter element, Figure 2 is a plan view from above of a tie tube of the filter assembly of Figure 1, and Figure 3 is a schematic cross-section, partly broken away, of a second filter assembly showing a housing, a casing and a filter element.
Referring to Figure 1, the first filter assembly comprises a housing indicated generally at 10, a casing indicated generally at 11, a filter element 12, an end cap 13 and a tie tube 14.
The housing 10 is made of metal, for example stainless steel, and comprises a container 15 and a lid 16. The container 15 has a circular base 17 surrounded by an annular side wall 18 which terminates at its upper end in an outwardly directed annular flange 19. The radially inner end of the upper surface of the outwardly directed flange 59 is formed with a step 20 for a purpose to be described below.
The lid 16 is generally circular with a diameter that is generally equal to the diameter of the container 15 across the flange 19. The lid 16 has an outer peripheral surface that mates with the flange 19 and can be connected to the flange 19 by fixing means, such as bolts (not shown) or clamps (shown schematically at 45). As seen in Figure 1, the lid 16 is provided with a step 21 that is in register with the step 20 in the annular flange 19 to form an annular channel extending around the container 15 between the flange 19 and the lid 16.
The casing 11 is formed from suitable plastics materials and comprises a head 22 and a bowl 23. The head 22 is moulded and comprises a generally disc-shaped body 24 formed with an inlet passage 25 and an outlet passage 26. The inlet passage 25 continues through an inlet tube 27 projecting upwardly from an upper surface 28 of the head 22. Similarly, the outlet passage 26 continues through an outlet tube 29 projecting upwardly from the upper surface 28 of the body 24. The inlet passage 25 and the outlet passage 26 both open on to lower surface 31 of the body 24.
Both the inlet tube 27 and the outlet tube 29 are provided at their upper ends with respective annular grooves 32 extending around the outer surface of the associated tube 27, 29. These grooves 32 are for receiving connectors (not shown) at the ends of respective inlet and outlet pipes to form fluid-tight couplings between such pipes and the tubes 27, 29. Of course, other end shapes could be provided for co-operation with different connectors.
The inner surface 31 of the body 24 is provided with an annular projecting knife edge 33. This extends into the filter element 12 in a manner that will be described below.
The bowl 23 is moulded from a plastics material. This may be translucent. The bowl 23 is of similar shape to the container 15 with a circular base 34 surrounded by an upstanding annular side wall 35 terminating at its upper end in an outwardly directed annular flange 36. The diameter of the bowl base 34 and the bowl side wall 35 are of lesser diameter than the diameter of the casing container base 17 and the container side wall 18. The bowl 23 is self-supporting which is to say that the bowl 23 will maintain its shape when standing on a surface at room temperatures and when not in use. In order to achieve this, the thickness of the bowl 23 may be generally greater than 0. 50mm.
The annular flange 36 of the bowl 23 is welded to the periphery of the lower surface 31 of the head 22. This thus forms a closed casing with access only through the inlet tube 27 and the outlet tube 29. As seen in the drawing, the welded peripheral edge of the head 22 and the bowl annular flange 36 are received within the channel formed between the steps 20, 21 in the housing 10. This locates the casing 11 in the housing 50.
The end cap 13 is moulded from a suitable plastics material and is generally disc- shaped. The end cap 13 has an upper surface 37 formed with an annular knife edge 38 and has an aperture 39 extending between the upper surface 37 and a lower surface 40. The aperture 39 is offset from the centre of the end cap 13 and its function will be described below. The filter element 12 is generally cylindrical with a cylindrical outer surface and with a cylindrical inner surface surrounding an open centre of the element 12. It may be formed from any suitable material such as fibres and may be either pleated or non- pleated. It may be provided with wraps and drainage layers as required. Suitable filter elements are known in the art and so the filter element 12 will not be described in any detail. A perforate core 30, which may be of a plastics material, supports the cylindrical inner surface of the filter element 12. The diameter of the cylindrical inner surface is such that the inlet tube 27 and the outlet tube 29 lie within an imaginary extension of the cylindrical inner surface.
The filter element 12 has an upper annular radially extending surface 41 and a lower annular radially extending surface 42. The knife edge 33 on the head 22 projects into the upper surface 41 and the knife edge 38 on the end cap 13 extends into the lower surface 42. The head 22 thus acts as an upper end cap for the filter element 12. This locates the filter element 22 relative to the head 22 and the end cap 13. The filter element 12 is held in this position by the tie tube 14 which is connected between the head 22 and the end cap 13. The tie tube 14, which is seen in cross section in Figure 2, comprises an outer tube 43 and an inner tube 44. As seen in Figure 2, the inner tube 44 has an axis which is offset from the axis of the outer tube 43 and a portion of the inner tube 44 is formed by a portion of the outer tube 43. The outer tube 43 has a diameter which is less than the inner diameter of the filter element 12 so that the inner surface of the filter element 12 is spaced radially outwardly of the outer surface of the outer tube 43. The diameter of the outer tube 43 is such that it encompasses the inlet passage 25 but is radially inwardly of the outlet passage 26. The inner tube 44 has a similar diameter to both the inlet passage 25 and the aperture 39 in the end cap 13 and is axially aligned with the inlet passage 25 and the aperture 39 so as to form a continuous closed passage between the inlet passage 25 and the aperture 39.
The tie tube 14 is welded at one end to the inner surface 31 of the head 22 and at the other end to the upper surface 41 of the end cap 13. This thus holds the filter element 12 in position on the head 22. In addition, the core 30 may also be so welded.
In use, the inlet tube 27 is connected, as described above, to an inlet pipe supplying fluid to be filtered. The outlet tube 29 is connected via a connector to a receiver for receiving filtered fluid. As will be seen, the inlet tube 27 has an axial length that is less than the axial length of the outlet tube 29. This allows the inlet tube 27 and the outlet tube 29 to be located close to one another on the head body 24 whilst still allowing sufficient access to attach the connectors.
Fluid is then pumped through the pipe and the inlet tube 27 before passing through the inner tube 44 of the tie tube 14 and the aperture 39 in the end cap 13. The inner tube 44 thus acts as a transfer tube to lead the fluid to the interior of the bowl 23 and allows it to pass through the space between the end cap 13 and the base 34 of the bowl 23 to the exterior surface of the filter element 12. The fluid then passes radially inwardly through the filter element 12, through the perforate core 30 and into the annular space between the core 30 and the outside of the outer tube 43 before leaving through the outlet tube 29 and the outlet pipe. When the filter assembly is non-operational, the part of the bowl 23 remote from the bowl flange 36 is, as seen in the drawing, spaced from the associated surfaces of the container 15. This spacing is sufficient to allow the bowl 23 to be lifted in and out of the container 15 and sufficiently small that if, at operating pressures, the bowl 23 is forced against the container 15, it is supported by the container 15. This action may also be influenced by the temperature of the filtered fluid ; where the fluid to be filtered is at a temperature higher than ambient temperatures, this will increase the flexibility of the bowl 23 and cause it to be forced against the container 15 although the bowl remains self supporting when not in use and at room temperatures.
When the filter element 12 needs changing, the connectors for the tubes are disconnected from the inlet tube 27 and the outlet tube 29. The lid 16 is removed from the container 15. The casing 11 can then be removed and disposed of in one piece. It is replaced by a fresh casing 11 with associated filter element 12, end cap 13 and tie tube 14, with the lid 16 being reconnected to the container 15 to close the housing 10. The inlet pipe and the outlet pipe can then be reconnected to the inlet tube 27 and the outlet tube 29 respectively and filtration of the fluid recommenced.
Referring next to Figure 3, the second filter assembly comprises a housing indicated generally at 50, a casing indicated generally at 51, a filter element 52, a lower end cap 53 and a tie tube 54.
The housing 50 is made of metal, for example stainless steel, and comprises a container 55 and a lid 56. The container 55 has a circular base 57 surrounded by an annular side wall 58 which terminates at its upper end in an outwardly directed annular flange 59. The radially inner end of the upper surface of the outwardly directed flange 59 is formed with a step 60 for a purpose to be described below.
The lid 56 is generally circular with a diameter that is generally equal to the diameter of the container 55 across the flange 59. The lid 56 has an outer peripheral surface that mates with the flange 59 and can be connected to the flange 59 by fixing means, such as bolts (not shown) or clamps (one of which is shown schematically at 95). As seen in Figure 3, the lid 56 is provided with a step 61 that is in register with the step 60 in the annular flange 19 to form an annular channel extending around the container 55 between the flange 55 and the lid 56. The purpose of this will be described below.
The casing 51 is formed from suitable plastics materials and comprises a head member 62 and a bowl 53. The head member 62 includes a body formed from any suitable plastics material with a moulded upper end cap 64 joined to a head moulding 65. The end cap 64 is a plate-like disc-shaped part and is provided with a hole 66 offset from the centre and extending between a first (lower) face 67 of the end cap 54 and a second (upper) face 68 of the end cap 64. An inner annular rib 69 surrounds the hole 66 on the second face 68. The second face 68 also carries an outer annular rib 70 having a larger diameter than the inner rib 69, surrounding the inner rib 69 and having its axis offset from the axis of the end cap 64.
The head moulding 65 is also a plate-like disc-shaped part but with a greater diameter than the upper end cap 64. The head moulding 65 has an upper surface 71 and a lower surface 72. An annular rebate 73 extends around the lower surface 72 at the periphery of the head moulding 65 for a purpose to be described below. The head moulding 65 is provided with an outlet hole 74 and an inlet hole 75. An inner annular rib 76 extends around the outlet hole 74 on the lower surface 72 of the head moulding 65 and is connected to the inner rib 69 on the upper end cap 64. The two ribs 69, 76 thus form a spacer that separates the upper end cap 64 and the head moulding 65 holding these parts parallel to one another. An outer annular rib 77 is also provided on the lower surface 72 of the head moulding 65. The outer annular rib 77 surrounds the inner annular rib 76 and is sized and located to be in register with and connected to the outer rib 70 on the end cap 64. The two ribs 70, 77 thus form a second spacer that separates the upper end cap 64 and the head moulding 65 to provide the body of the head member 67 with a hollow interior. In this way, the hole 66 in the end cap 64, the inner rib 69 on the end cap 64, the inner rib 76 on the head moulding 65 and the outlet hole 74 on the head moulding 64 form a continuous passage 99 through the head 62.
This passage is continued by an outlet tube 78 connected to and projecting upwardly from the upper surface 71 of the head moulding 65. In addition, the outer rib 70 on the upper end cap 64 and the outer rib 77 on the head moulding 65 together form a closed chamber 79 surrounding the inner ribs 69, 76. This reduces dead space.
As seen in Figure 3, the outer rib 77 passes adjacent to the inlet hole 75. An inlet tube 80 is in register with this inlet hole 75 and is carried on the upper surface 72 of the head moulding 65. Accordingly, the axis of the outlet and inlet tubes 78, 80 are parallel but spaced, and parallel to the axes of the end cap 64 and the head moulding 65. A circumferentially and radially extending passage 81 is thus formed between the end cap 64 and the head moulding 65 and leading from the inlet hole 75 to the periphery of the end cap 64 and extending generally normal to the axis of the inlet tube 80.
The outlet and inlet tubes 78, 80 may be shaped in a manner not shown to allow the attachment of connectors (not shown) at the end of respective inlets and outlet pipes to form fluid-tight couplings between such pipes and the tubes 78, 80.
The bowl 63 is moulded from a plastics material. This may be translucent. The bowl 63 is of similar shape to the container 55 with a circular base 84 surrounded by an upstanding annular side wall 85 terminating at its upper end in an outwardly directed annular flange 86. The diameter of the bowl base 84 and the bowl side wall 85 are of lesser diameter than the diameter of the casing container base 57 and the container side wall 58. The bowl 53 is self supporting which is to say that the bowl will maintain its shape when standing on a surface at room temperatures and when not in use. In order to achieve this, the thickness of the bowl 53 may be generally greater than 0. 50mm.
As seen in Figure 3, the diameter of the head moulding 64 is such that an outer peripheral portion of the head moulding 64 extends beyond the peripheral edge of the upper end cap 64. The annular flange 86 of the bowl 63 is welded to the lower surface 72 of this peripheral portion of the head moulding 65 with the flange 82 sitting in the rebate 73. This thus forms a closed casing with access only through the inlet tube 78 and the outlet tube 80. As seen in Figure 3, the welded peripheral edge of the head moulding 65 and the bowl annular flange 86 are received within the channel formed between the steps 60, 61 in the housing 50. This locates and supports the casing 51 in the housing 50.
The lower end cap 53 is moulded from a suitable plastics material. It is substantially the same (in this case identical in shape) to the upper end cap 64, to reduce the number of parts, except that it does not include the hole 66. Accordingly, parts common to the lower end cap 53 and the upper end cap 64 are given the same reference numerals and are not described in detail. As seen in Figure 3, the first surface 67 of the end cap 53 is the upper face and the second surface 68 is the lower face.
The filter element 52 is generally cylindrical. It may be formed from any suitable material such as fibres and may be either pleated or non-pleated. It may be provided with wraps and drainage layers as required. Suitable filter elements are known in the art and so the filter element 52 will not be described in any detail. A perforate core 87, which may be of plastics material, supports the inner cylindrical surface of the filter element 52.
The filter element 52 is formed with an upper annular radially extending surface portion 88 connected to the upper end cap 64 and a lower annular radially extending surface portion 89 connected to the lower end cap 53. As seen in Figure 3, the peripheral edge of the upper end cap 64 is in register with the exterior surface of the filter element 52. As also seen in Figure 3, the internal diameter of the filter element 52 is such that the outlet and inlet tubes 78, 80 lie within an imaginary extension of the interior surface of the filter element 52. Thus, the core 87 is located radially outwardly of the radially outer edge of the hole 66 in the end cap 64. Thus the outlet tube 78 communicates with the interior of the filter element 52.
The tie tube 54 is a cylindrical tube of plastics material extending through the centre of the filter element 12 and connected to the upper end cap 64 and the lower end cap 53. As seen in Figure 3, the diameter and position of the tie-tube 54 are such that the tie tube does not overlap the hole 66 in the end cap 64. Thus the tie tube 54 and the upper and lower end cap 64, 53 form between them a closed chamber surrounded by an annular volume formed between the exterior surface of the tie tube 54 and the core 87 of the filter element 52. The tie tube 54 may be welded to the upper and lower end caps 64, 53.
As seen in Figure 3, the outer surface of the filter element 52 is spaced from the inner surface of the bowl 63. The lower end cap 53 is also spaced from the base 64 of the bowl 63, although this need not be the case ; there may be no dead volume between the lower end cap 53 and the base 84.
In use, the inlet tube 80 is connected to an inlet pipe supplying fluid to be filtered. The outlet tube 78 is connected via a connector to a receiver for receiving filtered fluid. As will be seen, the inlet tube 80 has an axial length that is greater than the axial length of the outlet tube 78. This allows the inlet tube 80 and the outlet tube 78 to be located close to one another on the head 62 while still allowing sufficient access to attach the connectors. Fluid is then pumped through the pipes and the inlet tube 80 before passing through the second hole 75 and spreading radially outwardly and circumferentially to the edge of the upper end cap 64. The fluid then passes between the exterior surface of the filter element 52 and the interior surface of the bowl 64 before passing through the filter element 52 and the core 87 to the annular volume between the core 87 and the tie tube 54. From there, the filtered fluid exits via the hole 66, the hole 75 and the outlet tube 78. The head member 62 thus provides not only an end cap 64 for the filter element 52 but also a passage leading from the centre of the filter element to the exterior surface of the filter element.
The spacing between the bowl 63 and the container 55 is sufficient to allow the bowl 63 to be lifted in and out of the container 65 but is sufficiently small that if, at operating pressures, the bowl 63 is forced against the container 55, it is supported by the container 55. This action may also be influenced by the temperature of the filtered fluid ; where the fluid to be filtered is at a temperature higher than ambient temperatures, this will increase the flexibility of the bowl 63 and cause it to be forced against the container 65 although the bowl 63 remains self-supporting when not in use and at room temperatures. When the filter element 52 needs changing, the connectors for the tubes are disconnected from the inlet tube 78 and the outlet tube 80. The clamp 95 is removed to allow the lid 56 to be lifted from the container 55. The casing I I can then be removed as a unit and disposed of in one piece. It is replaced by a fresh casing 61 with associated filter element 52, an end cap 53 and a tie tube 54, with the lid 56 being reconnected to the container 65 to close the housing 50. The inlet pipe and the outlet pipe can then be reconnected to the inlet tube 80 and the outlet tube 78 respectively and filtration of the fluid recommenced.
It will be appreciated that the filter assemblies described above with reference to the drawings has a number of advantages. Since the bowl 23, 53 is self supporting, it can be manufactured accurately to fit inside the housing 10, 50 without the possibility of snagging or folding. In addition, the spacing between the bowl 23, 53 and the container 15, 55 can be accurately gauged to give a required level of support in operation.
The provision of a head 22, 52 with integral means for receiving connectors (the grooves 32 in Figure 1) obviates the need for a plenum chamber and so cuts down the number of parts. In addition, the provision of inlet and outlet tubes 27, 29, 80, 78 that extend through the housing minimizes spillage when changing filter elements since no fluid is left in the housing. The filter assembly uses a single filter element 12, 52 of large diameter which allows the annular gap between the filter element 12, 52 and the bowl 23, 53 to be kept to a minimum. This keeps the upstream volume of fluid to a minimum which is advantageous when the casing 11, 51 is being removed. In addition, the large diameter of the filter element 12, 52 allows the inlet passage 25, 80 and the outlet passage 26, 79 to be located within the inner diameter of the filter element 12, 52. The presence of the tie tube 14, 54 is also advantageous. This performs multiple functions in connecting the end cap 13, 53 to the head 22, 52 as well as providing support for the filter element 12, 52. It will be appreciated that, in Figure 1, the presence of the inner tube 44 within the outer tube 43 and, in Figure 3, the presence of the tie tube 54 itself, reduces the volume which can be occupied by fluid within the core downstream of the filter element 12, 52. This again reduces the volume of fluid taken when the casing 11, 51 is removed and disposed of.
The tie tubes 14, 54 need not be of circular cross-section. They could be of any cross- sectional shape. The tie tubes 14, 54 are not the only means that may be used to reduce the volume of the centre of the filter element 12. A solid member may be used. In addition, such a member need not be used with the filter assemblies described above with reference to the drawings. It could be used with any filter assembly comprising a housing containing a filter element and having an inlet for fluid to be filtered and an outlet for filtered fluid, the filter element having an open centre through which fluid flows in a path between the inlet and the outlet. In this case, the member need not extend the whole length of the centre, it could extend along only part of the length.
It will be appreciated that there are a number of variations that may be made to the filter assembly described above with reference to the drawings. Although there are advantages to having a single filter element 12, 52, there may be a plurality of filter elements. The container 15, 55 and the bowl 23, 53 are, as shown, circular, but they need not be circular ; they could be of any suitable shape. The tie tube 14, 54 is a preferred construction, but other arrangements may be used, particularly in Figure 1, for feeding fluid to the filter element 12, 52 and for removing filtered fluid from the filter element 12. In particular, the inlet and the outlet need not be in the head 22, 62 ; they could be elsewhere in the casing, or one might be in the head 22, 62 and the other in the bowl 23, 53. The bowl 11, 51 is described as self-supporting due to the thickness of the material of which it is made. It could be self supporting as the result of separately or integrally formed reinforcements or ribs or battens with thinner material between.
Although the filter element 12, 52 is described above in Figure 1 as having knife edges 33, 38 projecting into the upper and lower surfaces 41, 42, the knife edges may be omitted and the filter element 12 welded, bonded, glued or otherwise attached to the head 22 and the end cap 13. This is as shown and described in Figure 3. The filter element 12, 52 is described above as being cylindrical. It could be of any tubular shape, whether of circular internal and external cross-section or not. In this case, the inlet and outlet tubes 27, 29, 78, 80 will lie within an imaginary extension of the interior surface of the filter element at the end of the filter element 12, 52 adjacent the tubes.
The direction of flow may be reversed.
The second filter assembly of Figure 3 need not be as illustrated and described above.
The head member 62 may be configured other than as shown to provide a passage from the inlet tube 80 to the periphery of the filter element 52. The use of a spaced upper end cap 64 and head member 65 allows a reduction in the number of different parts manufactured (since the upper end cap 84 is substantially the same as the lower end cap 53) but this construction is optional.
In addition, the head member 62 may be used to provide inlet and outlet flow paths for filter assemblies other than those described in Figures 1 to 3 above. It could be used in a filter assembly comprising a housing containing any appropriate tubular filter element with a hollow centre, an interior surface and an exterior surface. In this case, the head member 62 provides an end cap for the filter element and also provides a first passage leading to the centre of the filter and a second passage leading to the exterior surface of the filter element.
The head member 62/end cap 53 combination may also be used to end cap filter elements other than those described above. In such a case, the filter element includes a tubular filter member having a first end and a second end. The first end is closed by a head member which provides a first passage and a second passage. The second end is closed by an end cap. The head member includes a part which is substantially the same as the end cap and has a hole leading to the first passage.
