GB2239612A

GB2239612A - Edge filter

Info

Publication number: GB2239612A
Application number: GB9000311A
Authority: GB
Inventors: Allan Beacham
Original assignee: MULTONE Ltd
Current assignee: MULTONE Ltd
Priority date: 1990-01-06
Filing date: 1990-01-06
Publication date: 1991-07-10
Also published as: GB9000311D0

Abstract

An inward flow edge filter comprises a stack of annular plates with resilient hooks 16 which snap into recesses 17 in adjacent plates to limit the axial separation of the plates when the filter is backwashed (Fig. 2 is exploded view). Projections 18 define the filtering gaps during filtration, the plates being pressed together by a spring, or by the pressure drop if plates have neutral buoyancy. During backwashing the fluid pressure on an impervious end plate opens the stack out to the limits allowed by hooks 16. The plates have aligned radially oriented openings 15 defining flow passages for filtrate. <IMAGE>

Description

Fluid Filter Elements This invention relates to filter elements for fluid and, in particular, filter elements which are designed to be cleaned by a backwash flow of said fluid.

There have been a number of proposals for filter elements which can be extended to open up filter gaps for cleaning by a backwash flow and, of these, the most successful to date have utilised springs to open up the filter gaps. However, these are too expensive and/or cumbersome for certain uses, for example, if filters are to be provided for use with individual water flow meters.

Other proposals have been made involving the use of annular plates arranged in a stack, but problems have been experienced with vibration and the opening up of the plates for backwash flow. According to one suggested arrangement, (e.g. as described in EP-PS 0159961) resilient balls are placed between alternate pairs of plates to overcome the opening problem, but this arrangement can be difficult to assemble.

An object of the present invention is to provide a filter element made up of a stack of plates which avoids the use of springs, resilient balls, or the like, is of simple construction, and is easy to assemble.

According to the present invention a filter element for fluid comprises a stack of plates linked together in spaced, face-to-face, relationship to define a series of filter gaps between said plates, each plate having at least one aperture through which fluid normally flows in one common, generally axial, direction, characterised in that the plates are loosely linked together by cooperating parts to permit a limited axial movement between adjacent plates whereby, for cleaning, the filter gaps between adjacent plates can be opened up to the limited extent, and wherein that end of the stack furthest downstream from a backwash flow through the filter element presents a wall against which said backwash flow will impinge, the arrangement being such that the plates are caused to be forced apart automatically to their limited extent by the pressure of the backwash flow.

Preferably, spring means are provided for urging the adjacent plates towards each other and in contact, via stop means, to define said filter gaps, the pressure of the spring means being selected to be less than the operating pressure of the backwash flow whereby, for efficient cleaning, the plates are forced apart automatically against the action of the spring means by the backwash pressure.

It is preferred, for manufacturing simplicity, that all the plates are identical and that they are each linked to their immediate neighbours.

In a preferred embodiment, the wall impinged by the backwash flow is an imperforate end plate or end cap, loosely linked to the adjacent end plate of the stack such that, when backwash flow through the element is initiated, the pressure exerted on the end cap causes it to be forced apart from its adjacent plate against the action of the spring means. Movement of the adjacent plate then causes it to be forced apart from the next adjacent plate and so on, whereby all the plates of the stack are progressively and automatically forced apart by said backwash pressure for cleaning.

Instead of spring means for urging the plates together, the plates may be designed to have substantially neutral bouyancy in the fluid to be filtered so that they are simply held together to define their filter gaps by the normal flow of fluid therethrough.

The cooperating parts on said elements may comprise interfitting formations which are of a resilient material, whereby they can be snap-fitted together, and said stop means may be provided on the plates so that, between them, said cooperating parts and said stop means limit the range of relative axial movement of adjacent plates from their closed position defining said filter gaps to their opened up position for backwash cleaning.

The filter elements may each further comprise means for limiting lateral movement of the plates one to another, which means are preferably integrally formed with the plates. Conveniently, such means comprise a central portion of each plate being of a common frusto-conical form, whereby ##jacont plates nest together and the cooperating walls thereof provide the required lateral stability.

The identical plates may each have a series of radially extending apertures which are aligned together when the plates are stacked together to provide a number of flow paths through the filter element.

Although the invention has been generally defined above, it is to be understood that it includes any inventive combination of the features set out above, or in the i dcs#rir-,t#-on.

In particular, it includes any filter element comprising a stack of plates which are mechanically linked such that they provide a fixed filter gap in normal operation, and an opened up cleaning gap automatically in response to the pressure of the backwash flow in a required direction on an end wall of the stack.

In order that the invention may be readily understood, a preferred embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view from above of a plate for a filter element; Figure 2, is a section along the line II-II of an exploded, stack of plates; and Figure 3 is an enlarged detailed view showing two possible cooperating formations for linking the plates together in a stack.

A filter plate generally indicated at 10 comprises a central frusto-conical portion 11 and a horizontal skirt 12.

Referring werticularly to Figure 1, it will be seen that the skirt has rounded, concave cut-away portions at spaced intervals 13 to leave rounded, convex stub portions 14 spaced around the edge of the plate. The plate 10 has a series of radially extending apertures 15 which, in this embodimer #, increase in width as they extend towards their respective stub portions 14.

E #ch stub portion 14 has an upwardly extending resilient clip 16 on its outermost edge and is formed with a de@ent @@ immediately below that clip, (see Figure 2). Small stop projections (e.g. ridges) 18 are formed on the upper face of each stub portion 14, and on the flat top 19 of the frusto-conical portion 11, (as shown in Figure 1), to determine the minimum distance between the plates when stacked together, thereby defining the filter gaps between the plates in normal operation.

Thus, to form a filter element, a required number of plates are nested and then loosely linked together by the clips 16, each said clip of one plate snapping into engagement with a respective detent 17 of the next adjacent plate.

Figure 3 shows, to the left and right hand side, two possible arrangments for the clips 16 and detents 17. In each arrangement, the clips 16 are resilient and have an inwardly directed tooth 16a which can snap into a recess defining the detent 17. It will also be seen how the projections 18 define the filter gap 20 when the plates 10 are urged together, and how this gap is opened up to an extent limited by the recessed detent 17 when the plates are fore apart by the backwash pressure for cleaning.

Once a stack of plates 10 is formed, the end plate whose frusto-conical cavity 21 is exposed is closed-off by an end wall in the form of an imperforate end cap 22 having its own clips 16 for engaging in respective detents 17 of said end plate. This end cap 22 may be supported on a central spigot 23, around which may be mounted a spring 24 for urging the plates together in their normal filter gap coniguration. However, this spring may have a reduced spring rake, o- possibly e'iminated altogethew, if the plates have virtual neutral bouyancy in the fluid to be filtered and are orientated vertically, because the plates can then be urged together by flotation forces.

In the normal filter position, with the stack of plates vertical, water flows from outside through the filter gaps 20 between the plates 10 and then upwardly, in a generally axial direction,through the apertures 15 in the plates (as shown in Figure 2) until said flow reaches the top of the filter, where it continues into an associated fluid system. However, for cleaning, the direction of fluid flow is reversed, to create a backwash flow, and this flow passes through the apertures and exerts pressure on the end cap 22. This pressure is higher than the spring rate of spring 24 if provided and hence causes said cap to be forced away from its adjacent end plate, against the action of said spring, whereby the gap between it and its associated plate is opened up to the limit determined by the clips 16 acting in their respective detents 17.The end plate will begin to act on its next adjacent plate, and so on in a chain reaction, progressively along the length of the stack of plates until all the gaps 20 are opened to their limited extent.

It will therefore be seen that the proposed construction provides a filter element comprising essentially a series of identical plates which can be easily manufactured and assembled into a stack of any desired length and which will automatically open up along the length of the stack when subjected to backwash flow.

Te stack of plates can be located in a cage, which can extend through cut-away portions 13, but it is believed that in many uses such a cage can be dispensed with, because the frusto-conical shape of the plates is such that lateral movement between them is limited. Not only does this reduce expense, but it provides the further possibility of having filters bent or curved along their length, and with this in mind the clips may be replaced by telescopically cooperating formations which can take the up positions of different lengths.

In another arrangement, the cooperating formations of detent and clip described above may be replaced by respective halves of a hinge.

Claims

A filter element for fluid comprising a stack of plates linked together in spaced, face-to-face, relationship to define a series of filter gaps between said plates, each plate having at least one aperture through which fluid normally flows in one common, generally axial, direction, characterised in that the plates are loosely linked together by cooperating parts to permit a limited axial movement between adjacent plates whereby, for cleaning, the filter gaps between adjacent plates can be opened up to the limited extent, and in that the end of the stack furthest downstream from a backwash flow through the filter element presents a wall against which said backwash flow will impinge in such a way that pressure of the backwash flow causes the plates to be forced apart automatically to their limited extent.
2. A filter element according to Claim 1, characterised in that spring means are provided for urging the adjacent plates towards each other and in contact, via stop means, to define said filter gaps, the pressure of the spring means being selected to be less than the operating pressure of the backwash flow whereby, for efficient cleaning, the plates are forced apart automatically against the action of the spring means by the backwash pressure.
3. A filter element according to Claim 1, or Claim 2, characterised in that, all the plates are identical, and in that said plates are each linked to their immediate neighbours.
4. A filter element according to Claim 3, characterised in that each said identical plate has a series Jf radially extending apertures which are aligned together when the plates are stacked together to provide a number of flow paths through the filter element.
5. A filter element according to any one of the preceding Claims characterised in that the end wall impinged by the backwash flow is an imperforate end plate loosely linked to its adjacent plate of the stack such that, when backwash flow through the element is initiated, the pressure exerted on the end plate causes it to be forced apart from its adjacent plate against the action of the spring means, movement of the adjacent plate then causing the latter to be forced apart from the next adjacent plate and so on, whereby all the plates of the stack are progressively and automatically forced apart by said backwash pressure for cleaning.
6. A filter element according to Claim 1, characterised in that said plates are designed to have substantially neutral bouyancy in the fluid to be filtered so that they are urged together to define their filter gaps by the normal flow of fluid therethrough.
7. A filter element according to any one of the preceding Claims, characterised in that said cooperating parts on said plates comprise interfitting formations which are of a resilient material to be snap-fitted together, and said stop means are provided on the plates so that, between them, said cooperating parts and said stop means limit the range of relative axial movement of adjacent plates from their closed position defining said filter gaps to their opened up position for backwash cleaning.
8. A filter element according to any one of the preceding Claims, wherein said plates have means for limiting their lateral movement one to another.
9. A filter element according to Claim 8, characterised in that said means for limiting lateral movement comprise a central portion of each plate being of a common frusto-conical form, whereby adjacent plates nest together and the corresponding walls thereof provide the required lateral stability.
10. A filter element for fluid constructed, arranged and adapted for use substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.