Patent Description:
It is known to provide a filter apparatus for filtering a liquid, such as water, to remove debris and contaminants. A filter media, such as sand, may be provided in a filter chamber. In order to suppress or inhibit biological activity, it is known to expose the filter liquid to ultraviolet light. However, this approach is not suitable for suppressing or inhibiting biological activity within the filter media.

<CIT> discloses a water treatment system comprising a filtration compartment, a transfer compartment and a purification compartment. Untreated water is contained in the filtration compartment as well as filtration media. An ultra-violet (UV) lamp is provided in the purification compartment. The transfer compartment <NUM> is separated from the purification compartment by a wall having a reflective coating to reflect UV light from the UV lamp.

<CIT> discloses a fluid treatment apparatus comprising first and second titanium mesh filters disposed in respective first and second chambers. A pair of elongate ultra-violet lamps extend along the upper and lower portions of each of the first and second chambers. A series of valves is provided to enable the direction of flow through the filters to be reversed to perform backwashing of each filter in succession whilst fluid flowing along the passage is filtered by the other filter.

<CIT> discloses a moving bed media filter having a plurality of UV light sources. The filter comprises a vessel including a filter chamber containing a media bed having an upper surface. A recirculation (airlift) tube supplies compressed air to the vessel to carry media, contaminants and/or solids upwardly within a recirculation tube.

<CIT> discloses filter elements having an open cell structure.

At least in certain embodiments, the filter apparatus described herein seeks to overcome at least some of the problems associated with the prior art.

The present invention relates to a filter apparatus and to a method as claimed in the appended claims.

According to ef the present invention there is provided a filter apparatus for mechanically filtering a liquid, the filter apparatus comprising:.

At least in certain embodiments, the steriliser unit may disinfect the filter elements. The steriliser unit may suppress or inhibit biological activity. At least in certain embodiments, the steriliser unit may kill or render inactive micro-organisms. The micro-organisms may include one or more of the following set: germs, bacteria, protozoa, alveolates, helminths, fungi and viruses. At least in certain embodiments, the micro-organisms may include parasitic alveolates, notably apicomplexan parasitic alveolates, such as Cryptosporidium. The filter apparatus may kill the micro-organisms at various stages in their life cycle, for example when they are cysts.

The filter apparatus may be configured to sterilise the filter elements in the filter chamber during filtration of the liquid. The liquid flows through the filter chamber and causes the filter elements to form a filter pack. The steriliser unit may sterilise the filter elements while they are in this filter pack. The steriliser unit is configured to extend at least partially into the filter pack formed in the filter chamber. The steriliser unit is located inside the filter chamber such that, in use, the filter elements form the filter pack around at least a portion of the steriliser unit.

Alternatively, or in addition, the filter apparatus may be configured to sterilise the filter elements in the filter chamber during a backwashing operation.

The filter apparatus may be suitable for filtering water in one or more of the following set: swimming pools, swimming baths, leisure pools, hot tubs, spas and leisure parks.

The steriliser unit is disposed inside the filter chamber. The filter apparatus may be configured such that, in use, the steriliser unit is at least partially surrounded by the filter elements in the filter chamber.

In use, the filter elements form a filter pack in the filter chamber. The steriliser unit is disposed proximal to a region where the filter pack forms. This may be advantageous since the steriliser unit may treat the filter elements while they are in the filter pack. The filter pack may be stationary and exposure of the filter elements to the steriliser unit may increase.

The filter chamber may comprise a liquid inlet and a liquid outlet. The steriliser unit may be disposed proximal to the liquid outlet.

The flow of liquid through the filter chamber may be an up flow, typically resulting in a filter pack forming in an upper region of the filter chamber. The steriliser unit may be disposed proximal to the upper region of the filter chamber.

The flow of liquid through the filter chamber may be a down flow, typically resulting in a filter pack forming in a lower region of the filter chamber. The steriliser unit may be disposed proximal to the lower region of the filter chamber.

The steriliser unit may comprise at least one light source for emitting UV light. The steriliser unit may be configured to perform ultraviolet germicidal irradiation. The steriliser unit may be configured, in use, to transmit UV light through a filter pack formed by the filter elements in the filter chamber.

The at least one light source may be configured predominantly to emit light having a wavelength of between <NUM> and <NUM> inclusive.

The filter apparatus may comprise means for reflecting light emitted from the at least one light source into the filter chamber. A reflective layer, for example comprising a reflective foil surface, may be provided. If the filter chamber is formed by a transparent sidewall, the reflective layer may be disposed around the outside of the sidewall. If the filter chamber is formed by an opaque sidewall, the reflective layer may be disposed on an inner surface of the sidewall.

The filter elements have an open cell structure. In use, the open cell structure may facilitate the transmission of the light through the filter pack. The filter elements may each comprise one or more filter cells. The filter elements may comprise a tubular element having one or more filter cells formed therein. The filter elements may comprise a planar element, such as a disc- or polygon-shaped element, having a plurality of filter cells formed therein.

Alternatively, or in addition, the filter elements may be at least partially UV transparent.

The filter elements may be at least partially UV transparent to facilitate the transmission of light emitted from the at least one light source through the filter pack.

The one or more filter cell may have a length greater than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The one or more filter cell can have a length which is less than or equal to <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The length of the one or more filter cell can be approximately <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The one or more filter cell may have a length in the range <NUM> to <NUM>, inclusive. In certain embodiments, the one or more filter cell may have a length of <NUM> and a diameter in the range <NUM> to <NUM>. The length of the one or more filter cell may correspond to a length of the mechanical filter element along its longitudinal axis.

The one or more filter cell can each have a cross-sectional area less than or equal to <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, or <NUM><NUM>. The cross-sectional area of said one or more filter cell is measured in a reference plane disposed perpendicular to a longitudinal axis of the mechanical filter element. The one or more filter cell can have a cross-sectional area greater than or equal to <NUM><NUM>, <NUM><NUM> or <NUM><NUM>. The one or more filter cell can have at least substantially the same cross-sectional area. The one or more filter cell can have a cross-sectional area in the range of <NUM><NUM> to <NUM><NUM>.

Alternatively, or in addition, the filter elements may be formed from a UV transparent (or semi-transparent) material. The filter elements may be formed from a material which is transparent (or semi-transparent) to UV light having a wavelength corresponding to the wavelength of the UV light output by the light source. The filter elements could be formed of glass, for example. However, it is envisaged that the filter elements would be moulded from a plastics material, for example using an extrusion process.

The filter apparatus may comprise means for introducing air into the filter chamber through one or more air inlets to agitate the filter elements.

The filter chamber may be at least substantially sealed. The air introducing means may be configured to draw air into the filter chamber as liquid is drained from said filter chamber. The means for introducing air into the filter chamber may comprise an air supply conduit having at least one air inlet for introducing air into the filter chamber.

A control unit may be provided for controlling activation of the steriliser unit. The control unit may be configured to control activation of a pump for suppling liquid to the filter chamber.

The control unit may be configured to activate the steriliser unit when the pump is operating.

According to a further aspect of the present invention there is provided a method of filtering a liquid, the method comprising:.

The method may comprise sterilising the filter elements in the filter chamber during a backwashing operation to clean the filter elements.

Sterilising the filter elements may comprise emitting light which is incident on the filter elements in the filter chamber. The light may be emitted by a light source disposed inside the filter chamber.

Sterilising the filter elements may comprise emitting ultraviolet (UV). The light emitted into the filter chamber may have a wavelength of between <NUM> and <NUM> inclusive.

The method may comprise sterilising the filter elements forming the filter pack. The filter chamber may comprise a liquid inlet and a liquid outlet. The steriliser unit may be disposed proximal to the liquid outlet.

The method may comprise activating a steriliser unit to sterilise the filter elements in the filter chamber.

The steriliser unit is disposed inside the filter chamber.

The flow of liquid through the filter chamber may be performed concurrent with sterilisation of the filter elements and/or the liquid.

The term "sterilising" and the derivatives thereof are used herein to refer to any process which kills or renders inactive micro-organisms. The term "disinfect" could also be used to describe this process.

Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term "controller" or "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Unless indicated to the contrary, references herein to a cross-section of the filter chamber refer to a transverse cross-section extending perpendicular to a longitudinal axis of the filter chamber. At least in certain embodiments, the filter chamber may have cylindrical symmetry about said longitudinal axis. The longitudinal axis is typically arranged substantially vertically, but other arrangements may also be useful.

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:.

A filter system S incorporating a filter apparatus <NUM> in accordance with an embodiment of the present invention will now be described with reference to <FIG>. The filter apparatus <NUM> is operable to perform mechanical filtration of a liquid, typically water W. The water W is illustrated in the accompanying figures by hatching.

In the filter system S shown schematically in <FIG>, the filter apparatus <NUM> is configured to perform mechanical filtration of the water W in a swimming pool <NUM>. The swimming pool <NUM> may, for example, be an above ground swimming pool <NUM>. It will be understood that the filter system S may be used in other applications, for example in an aquatics system. A pump <NUM> is provided for pumping unfiltered water W from the swimming pool <NUM> to the filter apparatus <NUM>. The pump <NUM> is operable to pump unfiltered water W from the swimming pool <NUM> to the filter apparatus <NUM>. The water W is mechanically filtered, and the filtered water W returned to the swimming pool <NUM>. The pump <NUM> is a fixed speed pump in the present embodiment, but alternative embodiments may use a variable speed pump. The pump <NUM> may be incorporated into the filter apparatus <NUM>.

As shown in <FIG> and <FIG>, the filter apparatus <NUM> comprises a filter housing <NUM> which defines a filter chamber <NUM> having a sidewall <NUM>. The filter chamber <NUM> in the present embodiment is a sealed chamber. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> and collectively form a mechanical filter. As described herein, the filter apparatus <NUM> is operable to filter the water W. The filter housing <NUM> comprises a tubular member <NUM> having a central longitudinal axis X-X arranged substantially vertically. The tubular member <NUM> defines the sidewall <NUM> of the filter chamber <NUM>. In the present embodiment, the filter apparatus <NUM> has a diameter of <NUM> (approximately <NUM>") and a height of <NUM> (approximately <NUM>"). The filter apparatus <NUM> is configured to process a flow of between <NUM><NUM>/hour and <NUM><NUM>/hour. An exploded view of the filter apparatus <NUM> is shown in <FIG>. The upper and lower ends of the tubular member <NUM> are sealed by an upper closure member <NUM> and a lower closure member <NUM> respectively to close the filter chamber <NUM>. A lower mesh <NUM> and an upper mesh <NUM> are provided to retain the filter elements <NUM> in the filter chamber <NUM>. The tubular member <NUM> has a substantially uniform cross-section along the central longitudinal axis X-X. Thus, the filter chamber <NUM> in the present embodiment has a substantially constant profile along the central longitudinal axis X-X. In the present embodiment, the tubular member <NUM> is in the form of a cylinder having a circular cross-section (i.e. a right circular cylinder). The filter chamber <NUM> may have different cross-sections, for example elliptical, rectangular or square. The tubular member <NUM> is illustrated as being transparent in the present embodiment. It will be understood that the tubular member <NUM> may be opaque.

As shown in <FIG>, the filter system S comprises a liquid supply conduit <NUM> for supplying unfiltered water from the swimming pool <NUM> to a liquid inlet <NUM> formed in the filter chamber <NUM>.

The filter system S also comprises a liquid return conduit <NUM> for returning filtered water from a liquid outlet <NUM> formed in the filter chamber <NUM> to the swimming pool <NUM>. The liquid inlet <NUM> is formed in the lower closure member <NUM> and the liquid outlet <NUM> is formed in the upper closure member <NUM>. During filtration, there is an up flow of water W through the filter chamber <NUM>. The unfiltered water W is introduced through the liquid inlet <NUM> at the bottom of the filter chamber <NUM>; and the filtered water W exits through the liquid outlet <NUM> at the top of the filter chamber <NUM>. The filter chamber <NUM> is sealed and the operating pressure is greater than atmospheric pressure when the pump <NUM> supplies unfiltered water W to the filter chamber <NUM>.

The filter apparatus <NUM> also comprises a drain conduit <NUM> for draining water from the filter chamber <NUM>. The drain conduit <NUM> may, for example, be connected to waste or to a sump for collecting waste water. A drain valve <NUM> is provided for selectively opening and closing the drain conduit <NUM>. The drain valve <NUM> in the present embodiment is manually operated, for example by operating a control lever. In a variant, the drain valve <NUM> may be actuated by a drain valve actuator, for example a first electromechanical actuator, such as a solenoid.

The filter apparatus <NUM> comprises means for introducing air into the filter chamber <NUM>. The air introduction means (denoted generally by the reference numeral <NUM>) comprises an air supply conduit <NUM> and a check valve <NUM>. The air supply conduit <NUM> is connected to one or more air inlets <NUM> for introducing air into the filter chamber <NUM>. As described herein, the air supply conduit <NUM> is configured to enable air to be drawn into the filter chamber <NUM> through the air inlets <NUM> by the reduced pressure in the filter chamber <NUM> caused by the water W draining from the filter chamber <NUM>. The air supply conduit <NUM> extends vertically and has an air intake <NUM>. In the present embodiment the check valve <NUM> is disposed at or proximal to the air intake <NUM>. The air inlets <NUM> may be formed in one or more distribution conduits (not shown) disposed at the base of the filter chamber <NUM>, for example extending radially outwardly from a central manifold. The check valve <NUM> enables one-way flow through the air supply conduit <NUM>. In particular, the check valve <NUM> is configured to allow air to enter the air supply conduit <NUM> and to prevent water exiting through the air supply conduit <NUM>. The check valve <NUM> may, for example, comprise a spring-biased closure member or a closure flap (not shown) configured to open to allow air to be drawn into the air supply conduit <NUM> and to close to prevent water W exiting through the air supply conduit <NUM>. The check valve <NUM> may, for example, comprise a ball for locating in a valve seat to seal the air supply conduit <NUM>. In an alternative embodiment, the check valve <NUM> may be replaced with a valve member which may be selectively opened and closed. In alternative embodiments, the check valve <NUM> may comprise an electromechanical actuator, such as a solenoid, for opening and closing the air supply conduit <NUM>.

As outlined above, a plurality of filter elements <NUM> are disposed in the filter chamber <NUM>. When the water W is introduced into the filter chamber <NUM>, the filter elements <NUM> form a filter pack <NUM>. In the present embodiment, the filter elements <NUM> have substantially neutral buoyancy and, due to the upwards flow of the water W through the filter chamber <NUM>, the filter pack <NUM> forms at the top of the filter chamber <NUM>, as illustrated in <FIG>. The filter elements <NUM> disposed in the filter chamber <NUM> may have a neutral buoyancy or a positive buoyancy in water. The flow of water W through the filter chamber <NUM> compacts the filter elements <NUM> together at the top of the filter chamber <NUM> and forms the filter pack <NUM>; the movement of the filter elements <NUM> within the filter pack <NUM> is restricted. The resulting filter pack <NUM> is substantially static and is suitable for performing mechanical filtration of the water W. In the present embodiment, the filter pack <NUM> has a depth of approximately <NUM> (approximately <NUM>").

As shown in <FIG>, the filter elements <NUM> have an open cell structure. In particular, the filter elements <NUM> each comprise one or more filter cells <NUM>. The filter elements <NUM> comprise a cylindrical wall <NUM> which is open at each end. The cylindrical wall <NUM> has a central longitudinal axis X-X and a substantially circular profile. The filter elements <NUM> each comprise a plurality of filter cells <NUM>. The filter cells <NUM> are open cells for trapping particulates and other debris suspended in the unfiltered water W to perform mechanical filtration. The filter cells <NUM> are elongated and in the present embodiment form conduits extending along the length of the filter element <NUM>. As shown in <FIG> the filter cells <NUM> each have a first end <NUM> and a second end <NUM>. A first cell opening <NUM> is formed at said first end <NUM> and a second cell opening <NUM> is formed at said second end <NUM>. Thus, the first and second ends of each filter cell <NUM> are both open. In a variant, the filter cells <NUM> could be open at the first end <NUM> and closed at the second end <NUM>. In a further variant, the first and second ends <NUM>, <NUM> of the conduit could both be open, but an intermediate closure wall could be disposed between the first and second ends <NUM>, <NUM> to form separate filter cells <NUM> separated from each other by the intermediate closure wall. The term "open cell filter element" is used herein to define the filter element <NUM>. Further details of filter elements <NUM> suitable for use in the filter apparatus <NUM> are disclosed in the Applicant's International patent application number <CIT>.

It will be understood that other types of filter element <NUM> may be used in the filter apparatus <NUM> described herein.

The filter apparatus <NUM> in the present embodiment comprises a steriliser unit <NUM> which is activated during filtration of the water W. The steriliser unit <NUM> comprises a light source <NUM>, a shield member <NUM> and an electrical connector <NUM>. The light source <NUM> is disposed inside the shield member <NUM>. The light source <NUM> comprises at least one UV lamp configured to emit UV light for sterilising the filter elements <NUM>. The shield member <NUM> is formed of quartz to enable transmission of the UV light emitted from the light source <NUM>. In the present embodiment, the steriliser unit <NUM> comprises two (<NUM>) tubes arranged alongside each other to form a UV lamp. The UV lamp in the present embodiment has a power rating of <NUM> Watts. The light source <NUM> may comprise a single lamp or more than two (<NUM>) lamps. The steriliser unit <NUM> could comprise more than one light source <NUM>. The light source <NUM> is configured to emit electromagnetic radiation in the ultraviolet (UV) range (i.e. electromagnetic radiation having a wavelength in the range <NUM> to <NUM>). In use, the UV light emitted by the light source <NUM> has germicidal properties and is effective in killing or rendering inactivate microorganisms, such as bacteria, germs, protozoa, helminths, fungi and viruses. Thus, at least in certain embodiments, the light source <NUM> may be germicidal. In certain embodiments, the emitted light may be short-wavelength ultraviolet (referred to as Ultraviolet C or UVC) having a wavelength in the range <NUM> to <NUM>. The ultraviolet light emitted by the light source <NUM> is effective in reducing or eliminating biological activity in the water W and/or in the filter elements <NUM>. An enlarged view of the filter pack <NUM> is shown in <FIG> when the light source <NUM> is activated in accordance with an aspect of the present invention.

As shown in <FIG> and <FIG>, the steriliser unit <NUM> in the present embodiment is provided inside the filter chamber <NUM> and is operable to emit UV light directly into the water W and directly into the filter elements <NUM>. The light source <NUM> is disposed centrally within the filter chamber <NUM> and extends along the longitudinal axis X-X in the present embodiment. The steriliser unit <NUM> is disposed within the filter chamber <NUM> proximal to or coincident with the region where the filter elements <NUM> congregate during filtration. The steriliser unit <NUM> may, for example, be disposed proximal to the liquid outlet <NUM>. In the present embodiment, the steriliser unit <NUM> is disposed in an upper portion of the filter chamber <NUM>. As described herein, the filter apparatus <NUM> in the present embodiment is configured to generate an up flow of water W which displaces the filter elements <NUM> into the upper portion of the filter chamber <NUM>. Thus, in use, the filter pack <NUM> is formed within the filter chamber <NUM> proximal to the light source <NUM>. A steriliser unit <NUM> could be provided at the bottom of the filter chamber <NUM>. The steriliser unit <NUM> could be activated when the filter chamber <NUM> is drained and the filter elements <NUM> collect at the bottom of the filter chamber <NUM>. Alternatively, if the filter apparatus <NUM> was configured to establish a down flow of the water W through the filter chamber <NUM>, the steriliser unit <NUM> could be provided at the bottom of the filter chamber <NUM> to emit UV light during filtration. In a further variant, the steriliser unit <NUM> could extend long the length of the filter chamber <NUM>.

The filter elements <NUM> disposed in the filter chamber <NUM> have an open cell structure which, in use, facilitates the transmission of the light emitted by the light source <NUM> through the filter pack <NUM>. The light may, for example, be transmitted through the open cells of the filter elements <NUM>. In certain embodiments, at least some of the light emitted by the light source <NUM> is transmitted at least partially through the filter pack <NUM>. At least some of the light emitted by the light source <NUM> may be reflected off the surface of the filter elements <NUM> promoting scattering of the light within the filter pack <NUM>. This may help to increase exposure of micro-organisms present on the filter elements <NUM> (both on external surfaces thereof and also on interior surfaces within the open cells) to the UV light emitted by the at least one light source <NUM>.

The provision of ribs on the outside of the filter elements <NUM> may help to maintain paths for transmission of the UV light between filter elements <NUM> disposed adjacent to each other within the filter pack <NUM>. The central location of the light source <NUM> within the filter chamber <NUM> helps to promote penetration of the UV light into the filter pack <NUM>. As shown in <FIG>, the filter pack <NUM> is at least partially illuminated by the light source <NUM> when the steriliser unit <NUM> is activated. A reflective layer may optionally be provided around the tubular member <NUM> to reflect light back into the filter pack <NUM>.

The filter elements <NUM> could be formed from a plastics material which is transparent or semi-transparent to UV light. At least some of the UV light emitted by the light source <NUM> may be transmitted through the filter elements <NUM> within the filter pack <NUM>. The filter elements <NUM> may be formed from a plastics material which is transparent (or semi-transparent) to UV light having a wavelength corresponding to the wavelength of the UV light output by the light source <NUM>. For example, the plastics material may permit transmission of UV light having a wavelength less than <NUM>. The filter elements <NUM> may, for example, be formed from UV transmitting acrylic, cyclic olefin copolymer (COC), or other plastics polymer.

As shown schematically in <FIG>, the filter apparatus <NUM> comprises an electronic control unit (ECU) <NUM> for controlling operation of the pump <NUM> and the steriliser unit <NUM>. The ECU <NUM> comprises a processor <NUM> and a memory <NUM>. The processor <NUM> is configured to activate the pump <NUM> to pump the water W through the filter chamber <NUM>; and to activate the steriliser unit <NUM>. As described herein, the steriliser unit <NUM> is activated by energizing the light source <NUM> to emit UV light while the water W is pumped through the filter pack <NUM>. Thus, mechanical and biological filtration may be performed simultaneously.

The operation of the filter apparatus <NUM> will now be described with reference to <FIG>. The filter apparatus <NUM> is illustrated in <FIG> filtering the water W from the swimming pool <NUM>. To perform filtration, the ECU <NUM> activates the pump <NUM> to supply unfiltered water W from the swimming pool <NUM> to the filter chamber <NUM>. The ECU <NUM> may also control a drain valve actuator <NUM> to close the drain valve <NUM>. Alternatively, or in addition, the ECU <NUM> may check that the drain valve <NUM> is closed prior to activating the pump <NUM>. The pump <NUM> supplies unfiltered water W into the filter chamber <NUM> and establishes an up flow of water W through the filter pack <NUM>. The unfiltered water W is mechanically filtered as it passes through the filter pack <NUM> and filtered water W exits the filter chamber <NUM> through the liquid outlet <NUM>. The filter elements <NUM> perform mechanical filtration by trapping particulates and other material suspended in the water W. The filtered water W is returned to the swimming pool <NUM> through the liquid return conduit <NUM>. The material filtered from the water W may be held between the filter elements <NUM> forming the filter pack <NUM>, or within the open filter cells <NUM> of each filter element <NUM> and within the filter channels formed by the external ribs. The upper mesh <NUM> prevents the filter elements <NUM> entering the liquid return conduit <NUM>.

The steriliser unit <NUM> is activated at the same time as the pump <NUM>. The light source <NUM> is energized and UV light is emitted directly into the filter pack <NUM>, as illustrated in <FIG>. The UV light has germicidal properties and is effective in sterilising the filter elements <NUM>. The UV light is effective in reducing or eliminating micro-organisms on the filter elements <NUM>. The micro-organisms may, for example, include germs, bacteria, protozoa, alveolates, helminths, fungi and viruses. At least in certain embodiments, the micro-organisms may include apicomplexan parasitic alveolates, such as Cryptosporidium. The UV light may also help to reduce or eliminate micro-organisms in the water W pumped through the filter chamber <NUM>. Thus, at least in certain embodiments, the steriliser unit <NUM> may sterilise both the water W and the filter elements <NUM>.

As shown in <FIG> and <FIG>, the filter apparatus <NUM> is periodically purged to expel filtered material to waste. To perform backwashing, the pump <NUM> is deactivated and the drain valve <NUM> opened. The steriliser unit <NUM> may optionally be deactivated in conjunction with the pump <NUM> being switched off, for example to help reduce power consumption. As illustrated in <FIG>, the water W flowing out of the sealed filter chamber <NUM> causes a drop in operating pressure within the filter chamber <NUM> to less than atmospheric pressure. The reduced pressure in the filter chamber <NUM> causes the check valve <NUM> to open and draws air into the filter chamber <NUM> through the air inlets <NUM> via the air supply conduit <NUM>. The air entering the filter chamber <NUM> forms a plurality of bubbles B which rise to the top of the water W in the filter chamber <NUM>. The air bubbles B rise through the water W and agitate the filter elements <NUM>, helping to break up the filter pack <NUM>. As shown schematically in Figure 3B, air continues to be drawn into the filter chamber <NUM> as the water W flows through the drain conduit <NUM>. The continuous agitation of the filter elements <NUM> during backwashing helps to dislodge filtered material, for example displacing particulates trapped in the filter cells <NUM> and in the filter channels between the external ribs. It will be appreciated that the water W in the filter chamber <NUM> continues to drain through the drain conduit <NUM>, such that the level of the water W continues to drop, drawing more air through the air supply conduit <NUM> and causing further agitation of the filter elements <NUM> within the filter chamber <NUM>. By agitating the filter elements <NUM>, material and debris filtered by the filter elements <NUM> is dislodged and returned to the water W within the filter chamber <NUM>. In certain embodiments, the pump <NUM> may continue to supply water to the filter chamber <NUM> during backwashing.

The introduction of air into the filter chamber <NUM> continues concurrently with drainage of the water W from the filter chamber <NUM>. By draining the water W through the drain conduit <NUM>, the material and debris is expelled from the filter chamber <NUM>. The filter elements <NUM> may thereby be cleaned ready to perform filtration. The agitation of the filter elements <NUM> continues until the water level in the filter chamber <NUM> drops below the height of the air inlets <NUM> or the filter chamber <NUM> is empty. The level of the water W drops below the height of the air inlets <NUM> and air is drawn freely into the filter chamber <NUM>. The pressure in the filter chamber <NUM> returns to atmospheric pressure and the check valve <NUM> closes. As shown schematically in Figure 3C, when the filter chamber <NUM> is completely drained, the filter elements <NUM> settle at the bottom of the filter chamber <NUM>. The lower mesh <NUM> prevents the filter elements <NUM> entering the drain conduit <NUM>.

Once the water W has drained to waste and the filter chamber <NUM> is empty, the drain valve <NUM> is operated to close the drain conduit <NUM> and the pump <NUM> is re-started. The pump <NUM> supplies unfiltered water W such that the filter chamber <NUM> is partially or completely re-filled with unfiltered water W. The drain valve <NUM> may be held open such that additional washing of the filter elements <NUM> may be performed and the water supplied by the pump <NUM> flushed directly to waste through the drain conduit <NUM>. The inlet for the liquid supply conduit <NUM> could extend upwardly into the filter chamber <NUM> to promote washing of the filter elements <NUM>. In alternative arrangements, the drain valve <NUM> may be closed before or concurrent with opening of the liquid return conduit <NUM>. The backwashing may optionally be performed more than once. For example, the filter chamber <NUM> may be partially or completely re-filled, the liquid return conduit <NUM> closed and the drain valve <NUM> re-opened. The backwashing of the filter elements <NUM> is the same as described above, as air is drawn into the filter chamber <NUM> to form bubbles B which agitate the filter elements <NUM>.

The pump <NUM> is re-started to pump water from the swimming pool <NUM> into the filter chamber <NUM>. The drain valve <NUM> is operated to close the drain conduit <NUM> and the filter chamber <NUM> is refilled with unfiltered water W. The filter elements <NUM> re-form the filter pack <NUM> and are operative to perform mechanical filtration of the water W since it flows upwardly through the filter chamber <NUM>. The steriliser unit <NUM> is activated and the light source <NUM> illuminated. The filtered water W is returned to the swimming pool <NUM> through the liquid return conduit <NUM>.

The filter apparatus <NUM> described herein incorporates a sealed filter chamber <NUM> capable of supporting an operating pressure greater than atmospheric pressure. It will be understood that the filter apparatus <NUM> may be modified such that the operating pressure in the filter chamber <NUM> is less than atmospheric pressure. In particular, the filter apparatus <NUM> may be reconfigured such that the filter chamber <NUM> is on the suction side of the pump <NUM>. For example, the pump <NUM> may be disposed in the liquid return conduit <NUM>. The other connections to the filter chamber <NUM>, including the air introducing means <NUM>, may remain unchanged in this arrangement.

A variant of the filter apparatus <NUM> is shown in <FIG> and <FIG>. The filter apparatus <NUM> in this variant has a diameter of <NUM> (approximately <NUM>") and a height of approximately <NUM> (approximately <NUM>"). The filter elements <NUM> are provided in the filter chamber <NUM> to form a filter pack <NUM> having a depth of approximately <NUM> (approximately <NUM>"). The light source <NUM> has a power rating of <NUM> Watts. The filter apparatus <NUM> according to this arrangement has a flow of between <NUM><NUM>/hour and <NUM><NUM>/hour.

To facilitate installation of the filter apparatus <NUM> described herein, the filter chamber <NUM> may be pre-charged at the assembly stage with an appropriate volume of the filter elements <NUM>. Thus, the filter elements <NUM> may be introduced into the filter apparatus <NUM> during assembly. The filter apparatus <NUM> may be shipped with the filter elements <NUM> in situ.

It will be understood that more than one of the filter apparatus <NUM> described herein may be arranged in series or in parallel to perform filtration. An array comprising a plurality of the filter apparatus <NUM> may be assembled depending on the volume of liquid to be filtered. In certain embodiments, the filter apparatus <NUM> may have a modular configuration to facilitate assembly of the array. A schematic representation of a filtration system S comprising a first filter apparatus <NUM> and a second filter apparatus <NUM> arranged in parallel is shown in <FIG>. The first and second filter apparatuses <NUM> are of the type described herein with reference to <FIG>. The parallel connection provides a combined flow of <NUM><NUM>/hour to <NUM><NUM>/hour. It will be understood that more than two of the filter apparatus <NUM> in accordance with the present invention may be combined to provide increased capacity.

The steriliser unit <NUM> has been described herein as being disposed inside the filter chamber <NUM>. In a variant, not according to the invention, the steriliser unit <NUM> could be provided outside the filter chamber <NUM>. For example, the steriliser unit <NUM> could be configured to emit ultra violet light into the filter chamber <NUM>, for example through a transparent or semi-transparent section of the sidewall <NUM>. The steriliser unit <NUM> could, for example, have an annular form for emitting light radially inwardly into the filter chamber <NUM>.

Claim 1:
A filter apparatus (<NUM>) for mechanically filtering a liquid (W), the filter apparatus (<NUM>) comprising:
a filter chamber (<NUM>) containing a plurality of filter elements (<NUM>) for filtering the liquid (W), the filter elements (<NUM>) each having an open cell structure; and
a steriliser unit (<NUM>) disposed inside the filter chamber (<NUM>) for sterilising the filter elements (<NUM>) in the filter chamber (<NUM>);
wherein, in use, the liquid (W) flows through the filter chamber (<NUM>) and causes the filter elements (<NUM>) to form a filter pack (<NUM>) in the filter chamber (<NUM>), the steriliser unit (<NUM>) being located inside the filter chamber (<NUM>) such that the filter elements (<NUM>) form the filter pack (<NUM>) around at least a portion of the steriliser unit (<NUM>), the steriliser unit (<NUM>) being configured to extend at least partially into the filter pack (<NUM>) formed in the filter chamber (<NUM>) .