The present invention relates to filters and in particular, but not exclusively, to canister-type in-line filters. The invention is particularly applicable to the field of water, and potable water, filtration.

Filters, and in particular water filters, are widely used in domestic and commercial settings to filter out impurities in fluids such as potable water, body fluids, e.g. blood, chemicals and/or water use in high-cleanliness applications, for example medical applications.

Water quality is also important for beverage machines, in particular because of the potential for components of the beverage machines to suffer from "scaling". Scaling is the term used to describe deposits of limescale, which can be extremely detrimental to the operation of beverage machines and may even cause permanent damage. Heating of water in a beverage machine increases the concentration of dissolved carbonate which reacts with dissolved calcium to form calcium carbonate precipitate or scaling.

Other constituents of typical feedwater might include organic compounds, chlorine and the like, which can have an effect on taste.

In situations were relatively large volumes of fluid need to be filtered, or where the fluid flow rate is relatively high, it is often more convenient to use a plumbed-in, continuous filtration system. Such systems are relatively well-known and generally comprise a filtration unit comprising an inlet aperture connected to the supply of fluid and an outlet aperture connected to a tap or device using the filtered fluid. A filter medium is contained within the filtration unit and is sealingly interposed between the inlet aperture and the outlet aperture such that in normal use fluid is only allowed to flow out through the outlet aperture after it has passed through the filtration medium. In use, filters need to be replaced periodically, for example if the filter medium has become clogged with filtered-out impurities, or where there is a risk of biological growth over extended periods of time.

Known filters comprise a generally cylindrical filter medium sealingly secured to a head portion having an inlet aperture and an outlet aperture which communicates with the filter medium in such a way that fluid flowing into the inlet aperture passes through the filter medium before passing out of the outlet aperture. The filter medium is normally encased in an inner housing which is sealed in a fluid-tight manner to the head portion. The combination of the head portion, cylindrical filter medium and inner housing is itself located in a protective outer tube.

Examples of known filter assemblies are disclosed, for example, in WO 201 1 /101652 A2 and WO 2015/107349 A2. In those documents, the combination of the head portion, cylindrical filter medium and inner housing is removably securable within the protective outer tube and can be removed and replaced when required. In other known arrangements, the filter medium is permanently secured within the protective outer tube, such that the whole filter assembly is replaced and discarded when a fresh filter medium is required.

It is an aim of the present invention to provide a filter assembly whose manufacture and construction is simplified as compared with the prior art, thereby offering possibilities of cost reduction, whilst providing the same advantages as the known filter assemblies.

In accordance with a first aspect of the present invention, a filter assembly comprises a blow moulded housing having an aperture and filter means sealingly secured in the aperture. By having a blow moulded housing, it is possible to reduce the number of components in the filter assembly and to simplify the manufacturing process.

Preferably, the filter means is sealingly secured in the aperture of the housing during the blow moulding of the housing.

In one embodiment, the filter means comprises a mounting portion having a fluid inlet and a fluid outlet, the mounting portion being sealingly secured in the aperture of the housing. The mounting portion has one or more projections and/or recesses around/into which the material forming the housing has flowed during the blow moulding of the housing.

In one embodiment, the filter assembly comprises a filter portion secured to the mounting portion and is located within the blow moulded housing.

Preferably, the filter portion is spaced from the blow moulded housing.

In one embodiment, the filter means and blow moulded housing are elongate. The filter means may comprise a pressure-limiting valve.

In one embodiment, the filter means comprises a fluid inlet and a fluid outlet, the filter means comprises a filter portion and the pressure-limiting valve is located between the fluid inlet and the filter portion.

In accordance with a second aspect of the present invention, a method of forming a filter assembly comprises locating a parison around a filter means, positioning the filter means and parison within a mould, applying blow moulding pressure through the filter means to expand the parison into contact with the moulding surface of the mould and sealingly securing the filter means to a part of the parison.

In one embodiment, the filter means is secured to a part of the parison during the blow moulding.

The method may comprise sealingly locating a portion of the filter means in an aperture of the closed mould during blow moulding and applying heat to that portion of the filter means. The mould may be provided with heating means in the vicinity of the aperture.

The parison may be tubular and/or may be extruded.

The filter means may comprise a mounting portion having a fluid inlet and a fluid outlet secured to the mounting portion, the mounting portion being sealingly located in the aperture of the mould during the blow moulding.

Conveniently, the blow moulding pressure may be applied through one or both of the fluid inlet and fluid outlet.

The mounting portion may have one or more projections and/or recesses around/into which the material forming the parison flows during the blow moulding.

The filter means may comprise a filter portion secured to the mounting portion and being located within the parison.

The filter means may be elongate. The filter means may comprise a pressure-limiting valve.

The filter means may comprise a fluid inlet and a fluid outlet, the filter means may comprise a filter portion and the pressure-limiting valve may be located between the fluid inlet and the filter portion.

By way of example only, specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figures 1 to 5 are schematic illustrations of the steps of a process for manufacturing a filter assembly, in accordance with the present invention;

Figure 6 is a perspective view of an embodiment of filter assembly in accordance with the present invention;

Figure 7 is a vertical cross-section through the filter assembly of Figure 6;

Figure 8 is a perspective view of the upper portion of the filter assembly of Figure 6; Figure 9 is a vertical cross-section through the upper portion of the filter assembly of Figure 6; and

Figure 10 is an exploded view of the filter assembly of Figure 6. Figures 1 to 5 are schematic illustrations for manufacturing a filter assembly in accordance with the present invention, such as the filter assemblies shown in Figures 5 and 6. The process is an extrusion blow moulding process and utilises a mould formed from two separable mould halves 10, 12 which, when joined, define the external shape of the filter assembly.

In Figure 1 , a preform 14 is inserted into the opened mould between the mould halves 10, 12. The preform 14 comprises a mounting means in the form of a generally circular, cylindrical moulded plastics plug 16 to the undersurface of which a conventional cylindrical filter medium 18 is sealingly and permanently secured. The preform 14 also has a fluid inlet 20 and a fluid outlet 22, and the interior of the preform is provided with fluid passages arranged so that fluid flowing into the inlet 20 passes through the filter medium 18 before being able to pass out through the outlet 22. It should also be noted that there is no fluid barrier outwardly of the filter medium 18. As will be explained, the fluid barrier is formed during the manufacturing process and also forms the protective outer housing of the filter assembly. It will also be observed that the moulded plastics plug 16 has a radially outwardly projecting circumferential rib 24 of rectangular cross section which, as will be explained, assists in anchoring the plug in place during the moulding process. The preform 14 is positioned so that the inlet and outlet 20, 22 project above the upper level of the mould halves 10, 12 and the upper portions 26, 28 of the mould halves 10, 12 are shaped to form a circular aperture of a diameter slightly greater than the circumferential rib 24. As shown schematically in the drawings, the periphery of the two halves of the circular aperture in the mould halves 10, 12 are each provided with an electric heating element 30.

In the second step of the process shown in Figure 2, a tubular parison 32 is extruded from an extruder 34 (shown schematically) around the preform 14. The material of the extruded parison is chosen to provide the necessary durability as it will ultimately form the outer housing of the valve assemblies, but examples of suitable materials for the parison are high density polyethylene and polypropylene, but other materials could be chosen, depending upon the performance requirements.

In the third step of the process, as shown in Figure 3, the two mould halves 10, 12 close against each other to form an internal void 36 having a wall which will correspond to the outer surface of the finished filter assembly. The aperture formed by the upper portions 26, 28 of the mould halves 10, 12 engages the portion of the parison immediately outward of the plug 16, and the aperture is shaped and dimensioned so that it squeezes and sealingly engages the upper portion of the parison and the plug 16.

In the fourth step of the process, as shown in Figure 4, a connector 38 having outlet ports corresponding to each of the inlet and outlet 20, 22 of the preform is positioned over the inlet and outlet 20, 22 such that they are sealingly received in recesses (not visible) in the connector 38. Hot air shown schematically at 40 is then introduced at relatively low pressure into the connector 38, and the hot air then passes through the inlet and outlet 20, 22 and through the filter medium 18, such that the parison is expanded outwardly into contact with the internal wall of the mould. At the same time, the heating elements 30 which effectively encircle the aperture in the top of the mould in which the plug 16 is located heats the portion of the parison immediately radially inwardly and ensures that the parison is permanently secured to the plug 16. The heating elements 30 cause the upper portion of the parison to melt partially and form around the periphery of the plug, and the circumferential rib 24 of the plug helps to ensure that the upper portion of the parison is permanently, securely and sealingly attached to the periphery of the plug around its whole circumference. In the fifth step of the process, shown in Figure 5, the mould halves 10, 12 are separated and the finished filter assembly 44 is removed. As indicated in Figure 5, the material of the parison encases, but is separated from, the filter medium 18, and also extends over the side wall of the plug 16. The inlet and outlet 20, 22 are not covered by the material of the parison and, as indicated in Figure 5, project above the upper level of the finished filter assembly, for connection to inlet and outlet lines in a conventional manner.

The filter assembly formed by the above process thus has a robust outer casing formed by blow moulding of the parison. The process reduces the number of components required in manufacture as compared with the prior art filter assemblies, which have a separate outer housing and which require manual assembly. The filter assembly of the present invention has fewer components to dispose of, when replacement is required, and removal and replacement is facilitated as compared with some prior art filter assemblies, since the whole assembly is disposed of and replaced by an entirely new filter assembly when required.

Figures 6 to 9 illustrate one particular embodiment of filter assembly, manufactured in accordance with the present invention. The filter assembly has a short cylindrical moulded plastics (high-density polyethylene, for example) upper plug 52 to the undersurface of which a cylindrical conventional carbon filter 54 is fixedly secured. A fluid inlet 56 and fluid outlet 58 project upwardly from the upper face of the plug 52 are each provided with a number of O-ring seals 60 for sealing connection of the fluid inlet and fluid outlet respectively (not shown). As best seen in Figure 9, a pressure limiting valve 62 is provided within the body of the plug 52 in communication with the fluid inlet 56, which limits the maximum pressure of fluid supplied to the filter medium 54, thereby preventing damage from excess pressure.

A continuous outer housing 64, formed by the blow moulding process explained above, is moulded to the periphery of the plug 52 and extends over the entire filter medium 54, being spaced apart from it. As best seen in figure 9, the plug 52 is provided with a plurality of radially extending circumferential ribs 66 and recesses 68 into which the material of the parison forming the outer housing flows during the blow moulding process, providing a secure key to maintain the plug 52 in sealing contact with the outer housing 64.

As best seen in the exploded view of Figure 10, the pressure limiting valve comprises a valve closure member 70 seated in a tubular guide 72. The valve closure member 70 carries two O-ring seals 74, 76 and a packing block 78. A compression spring 80 seated in a chamber 82 within the plug 52 engages an upper circumferential rib 84 which in conjunction with the piston determines the maximum pressure which can be applied to the filter medium 54. A large O-ring 85 for sealing between the filter medium 54 and the plug 52 is provided. Each of the fluid inlet and fluid outlet 56, 58 also receives a push fit connector 86, 88, for connecting to inlet and outlet pipes respectively.

Fluid entering the filter assembly via the fluid inlet 56 enters the space 90 between the filter medium and the inner surface of the outer wall. It then passes inwardly through the filter medium 52, which has a central elongate passage 92 connected to the fluid outlet 56, by means of which fluid filtered by the filter medium 52 passes out of the filter assembly.

The filter assembly of the present invention has fewer components than the prior art filter assemblies and can be manufactured in fewer steps, thereby reducing the cost of production. At the same time, however, the blow moulded outer housing provides protection for the filter medium and the robust seal between the plug and the blow moulded outer housing, formed during the blow moulding process ensures that fluid does not leak during use of the filter assembly. The invention is not restricted to the details of the foregoing embodiments.