The present invention relates to filtration. An example of such filtration is the filtering of fluid transmitted within a fluid conduit such as a pipe. Applications for this kind of filtration are manifold and include, typically though by no means exclusively, the filtration of fluids transmitted in the power generation industry. Fluid which is transmitted for the purpose, say, of driving a turbine is typically filtered to remove particulate matter which may, if it enters the turbine chamber, either impede turbine operation or even damage the turbine.

Filtration of solid material within a conduit is performed by capturing it with a filter as it passes along the conduit. Typically, a filter is provided by a mesh, for example, with the mesh size determining the size of particulate matter or other material which is to be captured. Because the filter presents a barrier through which the fluid must flow when travelling along through the conduit, it inevitably provides a resistance fluid flow. That resistance increases as particulate matter is captured within the filter, causing increasing numbers of the apertures in the filter through which the fluid flows to become blocked. It follows, therefore, that any filter has a finite lifetime during which it can efficiently operate to capture particulate matter and, at the same time, permit the flow of fluid through the conduit. That lifetime can be increased by increasing the surface area of the filter, since this provides a greater number of apertures through which fluid can flow and thus increases the time taken to block a sufficient number of apertures within it to reduce the fluid flow to unacceptable levels. One way of increasing filter surface area is to shape the filter so that it extends in three dimensions within the conduit, meaning that, in addition to extending across the conduit in a transverse plane, it also projects axially along the conduit. One typical geometry that enables this is a frusto-conical filter, though this is by no means the only such possible geometry.

Where the filter aperture size needs to be small, it is frequently the case that a filtering membrane is required, which very usually, is correspondingly delicate. Such delicate membranes may lack the strength to retain their frusto-conical shape against the pressure arising from the fluid flow through them. Additionally, it may also be the case that the delicate nature of the membrane means that it is vulnerable to being punctured by larger, heavy objects flowing through the conduit. Accordingly, where a fine filter membrane is used, it may require structural support, by a suitable relatively rigid frame. The frame will usually have the same geometry as that desired for the filter membrane and, necessarily, will also have apertures through which the fluid can flow. The size of apertures in the frame will typically be selected to be as large as possible, but nonetheless sufficiently small that the frame apertures will act to

104573577V2 prevent the passage of larger objects which might puncture the membrane. In either case (i.e. whether it is a coarse filter or not) the frame also provides additional, undesirable resistance to the flow of fluid through the conduit. Frequently, the support is simply a coarser filter, which may be used in conjunction with a fine membrane or, alternatively, may be used on its own.

A first embodiment of the present invention provides filtration apparatus for filtering fluid passing through a conduit comprising: a fine filter comprising a first web extending across the conduit and having a plurality of relatively fine apertures; a support which acts as a coarse filter and also supports the fine filter, the support having a second web which extends transverse to the conduit axis, axially within the conduit and has a filtering surface inclined to the conduit axis, wherein the support has apertures being provided by bores within the filtering surface of the second web, the bores having, when viewed axially with respect to the conduit, a substantially circular cross section.

Further embodiments of the present invention provide further aspects of such an apparatus, and accordingly a further embodiment provides filter for use within a fluid conduit, the filter having a web which extends transverse to the conduit axis, axially within the conduit and has a filtering surface inclined to the conduit axis, the filter having apertures being provided by bores within the filtering surface of the web, the bores having, when viewed axially with respect to the conduit, a substantially circular cross section.

Embodiments of the invention will now be provided, with reference to the accompanying drawings, in which:

Fig. 1 is a section through a fluid conduit equipped with a filter and support;

Figs. 2A - C show the support of Fig. 1 in more detail;

Fig. 3 illustrates an element of support of Figs.2

Fig. 4 is a further detail of Fig. 1 ;

Fig. 5 is a detail of a first embodiment of the present invention;

Figs. 6A - C illustrate the support of Fig. 5;

Fig. 7 illustrates an element of the support of Figs.6;

Fig. 8 is a detail of a further embodiment of support according to the present invention;

Figs. 9A - C illustrate the embodiment of support from Fig. 8; and

Fig. 10 is a section through a modification to the embodiment of Figs. 5 to 7.

Referring now to Figs. 1 to 3, a fluid conduit is provided by a cylindrical pipe 10 having two parts 10A.B, interconnected by means of flanges 12A.B. Fluid flows through the pipe 10 from left to right in the drawing (though the invention functions equally with fluid flowing in the opposite direction - a preferable, though not essential feature being that the mesh is located on the 'inflow' side of the support) and to prevent the passage of unwanted solid matter a filter apparatus 14 is positioned inside the pipe. The filter apparatus includes a filter membrane 6, in this example provided by a fine wire mesh which defines a plurality of fine apertures through which the fluid can pass. The membrane extends across the entire cross-section of the pipe 12 but also projects axially with respect to the pipe axis A and, in the illustrated example, therefore has a frusto-conical shape. In the illustrated embodiment, therefore, the filter has two filtering surfaces: surface S1 having the form of a disc which extends in a plane orthogonal to the conduit axis; and surface S2, an annular segment (when viewed in two dimensions) which extends at an inclined (i.e. non-orthogonal) angle to the conduit axis. This geometry of membrane enables the filter to have a larger number of apertures through which the fluid can pass and, as a result, means that the increase in the pressure drop across the pipe (i.e. from the inflow side of the filter apparatus to the outflow side) increases more slowly as the apertures in the filter become blocked by solid material captured in the membrane's apertures.

Because the mesh providing the membrane 16 is relatively fine, the membrane is relatively delicate and, in the present example is unable to retain its frusto-conical form against the force applied by the flow of fluid through it - which of course increases as the filter apertures become blocked with captured solid material. The filter membrane 16 is therefore carried upon a support member 20. The support 20 is retained within the conduit by clamping its peripheral flange 16A between the flanges 12A.B. Typically, though not essentially, the support 20 will have the same or a similar geometry to that of the filter membrane and this is the case in the illustrated example. Referring now additionally to Figs 2A - C and 3, the support 20 has a frusto-conical shape, so that the support has filtering surfaces F1 and F2 corresponding to surfaces S1 and S2 respectively. The support is provided by a web 30 of relatively strong, relatively rigid material (in this case stainless steel, though other materials may be used such as other metals, carbon fibre and suitable plastics material, for example, depending upon the applied use) having a series of relatively large (that is to say by reference to the apertures in the filter membrane 16) apertures 32. The filtering surface F2 of the web 30 has the shape of a segment of an annulus which, upon welding the two straight edges to each other, creates a conical part of the web 30. The apertures 32 are circular and their size is typically selected to be as large as possible in order to reduce resistance to fluid flow while being sufficiently small to enable the support 20 firstly to provide support to the filter membrane 16 against the force due to the fluid flow so that it can retain its shape and secondly to act to prevent the passage of larger objects which might otherwise, due to their momentum, puncture the filter membrane 16. A typical size for such apertures may be in the region of 2 - 3mm though apertures of significantly greater and smaller size are apt to be used depending upon the application. To this extent, therefore, the support also acts as a filter so that there are two filters positioned one after the other. Equally, for coarse filtering applications, the support 20 may be used without a mesh or other form of fine filter, and thus simply functions as a relatively rigid, relatively strong, coarse filter.

Referring now, additionally to Figure 4, the general direction of fluid flow through the pipe 12 is parallel to the axis A. It will, however be appreciated that, because of the frusto-conical geometry of the membrane 16 and support 20 that, locally, the fluid may flow in different directions. Thus, the fluid will flow through the filtering surface S1 of the membrane 16 and then, in order to pass through the apertures 32 will then tend to flow axially through bores in the filtering surface F2 of the web 30 which provide those apertures whereupon, upon passing through them, it will once again flow axially. This "Z" - shaped pathway, which results from the bore which provides the aperture 32 extending at an angle relative to the axis A (since they are machined in the illustrated example, normal to the plane of the filtering surface F2) necessarily offers resistance to the fluid flow through the pipe 12. By contrast, the apertures within the membrane 16 do not offer as significant a level of resistance because the dimension of the mesh forming the membrane and therefore defining the apertures within it is sufficiently small that the fluid will pass through it with only minimal trans-axially diversion.

Referring now to Figures 6A and B, in a modified form of support 20 consistent with a first embodiment of the present invention has a filtering surface F2 having a plurality of apertures 32 which have an obround shape, with the parallel sides extending substantially parallel to the axis A. is formed with a substantially elliptical geometry, whereby the largest dimension within the ellipse extends substantially parallel to the axis A. Referring now additionally to Figures 6A - C and Figure 7, filtering surface F2 of support 20 is constructed from a web 60 of stainless steel, in which a plurality of such obround apertures 62 are, aligned in such a manner that when the straight edges of the web are attached to each other to form a frusto-conical support - so that the surface F2 is inclined to the conduit axis A - the apertures all extend with their single largest dimension substantially parallel to the axis A.

Referring to specifically to Figure 6B, it can be seen that as a result of this revised geometry of aperture, when viewed in an axially direction, each of the apertures 62 has a substantially more circular cross section when compared with the laterally extending (with respect to the axis A) elliptical shapes presented by the apertures 32 of the web 30 (illustrated in Figure 2B). This revised apertures geometry therefore offers less resistance to the flow of fluid through the conduit, since it requires a smaller movement of the fluid transverse to the Axis as it passes through the support. In a modification, the surface F2 has elliptical apertures.

In a preferred embodiment of the present invention, fluid flow resistance is further reduced by aligning the bores within filtering surface F2 so that they are aligned substantially co-axially with the axis A of the fluid conduit. Referring now to Figure 8, it can be seen that an aperture 82, formed within surface F2 of a web 80, which is used to provide a support, is created by a through-bore whose axis extends substantially parallel to that of the conduit axis A. Referring additionally to Figures 9A - C, a support having a plurality of apertures of this configuration is illustrated. Referring now specifically to Figure 9B, it can be seen that, when viewed axially, each of the apertures presents a perfect circle to the oncoming fluid which therefore further reduces motion of the fluid transverse to the axis during passage through the support and thereby further reduced the pressure drop across the filtering apparatus whether including a membrane in addition to the support, or the support is used on its own as a filter. In pressure testing the support structure illustrated in Figs. 9 has been shown to result in a drop in pressure across the support during fluid flow of up to 50% by comparison with the convention support of Figs. 2 (though the invention is not limited in this respect). The use of a such a support therefore is of considerable assistance in reducing unwanted pressure differential across a filtering apparatus which would otherwise require the expenditure of additional energy to force fluid through it.

The support of figures 9A - C can be manufactured in a number of ways. In one preferred embodiment, manufacture is undertaken by "3D printing". This can be performed using a number of materials including suitably rigid plastics materials and resin-bound metals. Where desired, however, the bores can be machined in a web in a conventional manner.

Referring now to Fig. 10, a modification of the embodiment of Figs 5 to 7 is illustrated. In one example of the embodiment of those figures, the obround, elliptical (or other similar such shapes) are created by punching out holes in the web 60. In order to increase fluid flow it is possible then to deform (for example by applying a suitable impact impulse) the rounded ends of the obround apertures in mutually opposing directions, which thereby causes the apertures to take on a shape which acts to divert fluid through them in a more linear manner.

The present invention has been illustrated with reference to supports and filter membranes having a frusto-conical shape. It is, however, equally applicable to supports of any geometry which have filtering surfaces which incline relative to a conduit axis, and thus includes two- serially connected cones (wherein one is inverted with respect to the other), a V-shape which therefore only inclines in two dimensions rather than three and a dome, for example.

The use of a fine filter in conjunction with a support is, in the examples illustrated, shown by the use of only a single fine membrane. Plural membranes may be used. For example, a series of three fine mesh filter membranes may be employed: a fine mesh membrane of 0.3mm sandwiched between two mesh membranes of 1 mm with the 1mm membranes serving to protect the finer mesh from contact with the support surface and larger objects flowing through the fluid.

It is to be understood that the different features of the various embodiments of the invention as described above are not necessarily limited to their association with the embodiments in connection with which they were first described. Thus, aspects of embodiments such as modifications are generally applicable to other embodiments of the invention described herein.