Patent Description:
A floating media hourglass biofilter is known from <CIT>. The biofilter comprises a tank having a hourglass profile to form a filtration chamber and an expansion chamber. A washing throat is formed in the tank to define the hourglass profile. A floating filter media in the form of solid pellets is provided in the tank to form a media pack in the filtration chamber. An air inlet line is connected to the tank for drawing air into the expansion chamber and disturbing the floating media pack inside the filtration chamber during backwashing of the biofilter. A sludge valve is opened allowing water to drain from the tank. A negative pressure is thereby established in the tank and air is drawn into the expansion chamber from atmosphere. The level of the water in the tank drops and the floating media travels from the filtration chamber into the expansion chamber. The washing throat promotes turbulence to fluidize the media pack. The downward expansion of floating media into the expansion chamber shearing biofloc and captured suspended solids from the solid pellets.

The washing throat forms a restriction in the filter chamber which impedes the movement of the filter media as the water level in the tank decreases. As the water level drops below the washing throat, the filter media are released into the expansion chamber. The backwashing relies on the increased excitation during this transition to shear biofloc from the exterior of the filter media. This backwashing strategy has been developed for pellets adapted to perform biological filtration. However, this approach may not be appropriate for other types of filter elements, for example configured to perform mechanical filtration.

Other relevant documents are <CIT>, <CIT>, <CIT> and <CIT>.

It is against this backdrop that the present invention(s) have been conceived. At least in certain embodiments, the present invention seeks to overcome or ameliorate at least some of the problems or limitations associated with prior art filters.

Aspects of the present invention relate to a filter system and a method of filtering a liquid as claimed in the appended claims.

The flow rate per unit cross-sectional area of the static filter pack may be greater than <NUM><NUM>/m<NUM>/h, <NUM><NUM>/m<NUM>/h, <NUM><NUM>/m<NUM>/h, <NUM><NUM>/m<NUM>/h or <NUM><NUM>/m<NUM>/h. The flow rate per unit cross-sectional area of the static filter pack may be in the range <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h exclusive. The flow rate per unit cross-sectional area of the static filter pack may be in the range <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h exclusive. The flow rate per unit cross-sectional area of the static filter pack may be in the range <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h; or <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h; or <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h; or <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h; or <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h. The flow rate per unit cross-sectional area of the static filter pack may be approximately <NUM><NUM>/m<NUM>/h. The method may comprise introducing air into the filter chamber through one or more air inlets to agitate the filter elements. The static filter pack may be formed in a filter chamber. The method may comprise allowing air to be drawn into the filter chamber as liquid is drained from the filter chamber. A liquid return valve may be provided for controlling the return of filtered liquid from the filter chamber. The air may be drawn into the filter chamber through an air supply conduit connected to a liquid return conduit connected to the filter chamber. 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 mechanical filter apparatus <NUM> in accordance with an embodiment of the present invention will now be described with reference to <FIG>. The mechanical 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 mechanical filter apparatus <NUM> is configured to perform mechanical filtration of the water W in a pair of aquaria <NUM>. The aquaria <NUM> in the illustrated arrangement are connected in parallel to the mechanical filter apparatus <NUM>. The aquaria <NUM> may be installed in a commercial outlet, such as a pet store. It will be understood that the mechanical filter apparatus <NUM> could be used to filter water in two or more aquaria <NUM>. The aquaria <NUM> could, for example, be arranged in a rack and arranged in one or more columns and/or rows. It will be appreciated that the mechanical filter apparatus <NUM> could be used to filter water in a single aquarium <NUM>. The mechanical filter apparatus <NUM> can be used to perform filtration in other applications, for example to filter the water in a swimming pool.

A pump <NUM> is provided for pumping unfiltered water W from the aquaria <NUM> to the mechanical filter apparatus <NUM>. The pump <NUM> is operable to pump unfiltered water W from the aquaria <NUM> to the mechanical filter apparatus <NUM>. The water W is mechanically filtered and the filtered water W returned to the aquaria <NUM>. The pump <NUM> is a variable speed pump in the present embodiment, but alternative embodiments may use a fixed speed pump. The pump <NUM> may be incorporated into the mechanical filter apparatus <NUM>.

As shown in <FIG> and <FIG>, the mechanical filter apparatus <NUM> comprises a filter housing <NUM> which defines a filter chamber <NUM> having a sidewall <NUM>. The filter chamber <NUM> is a sealed chamber capable of supporting an operating pressure greater than atmospheric pressure. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> and collectively form a mechanical filter. As described herein, the mechanical filter apparatus <NUM> is operable to filter the water W; and to backwash the filter elements <NUM> to remove filtered material. 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>. 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>. 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 mechanical filter apparatus <NUM> comprises a liquid supply conduit <NUM> for supplying unfiltered water from the aquaria <NUM> to a liquid inlet <NUM> formed in the filter chamber <NUM>. The mechanical filter apparatus <NUM> also comprises a liquid return conduit <NUM> for returning filtered water from a liquid outlet <NUM> formed in the filter chamber <NUM> to the aquaria <NUM>. In the present embodiment, an outlet of the liquid return conduit <NUM> is located above the level of the water W in each of the aquaria <NUM>. It will be appreciated that the outlet of the liquid return conduit <NUM> may be located below the level of the water W in each of the aquaria <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>, as illustrated in <FIG>. 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 mechanical 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. In the present embodiment, the drain conduit <NUM> is connected to the liquid supply conduit <NUM> such that the filter chamber <NUM> is drained through the liquid inlet <NUM>. In alternative embodiments, a separate drain outlet (not shown) may be provided, for example at the bottom of the filter chamber <NUM>. A drain valve <NUM> is provided for selectively opening and closing the drain conduit <NUM>. The drain valve <NUM> could be manually operated, for example by operating a control lever. In the present embodiment, the drain valve <NUM> is actuated by a drain valve actuator <NUM>, for example a first electromechanical actuator, such as a solenoid. An inlet mesh <NUM> and an outlet mesh <NUM> are provided to retain the filter elements <NUM> in the filter chamber <NUM>.

The mechanical 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> disposed at the top of the filter housing <NUM> above the filter chamber <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> and <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.

With reference to <FIG>, <FIG>, <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 suitable filter elements <NUM> are disclosed in the Applicant's International patent application number <CIT>, the contents of which are incorporated herein in their entirety by reference. It will be understood that other types of filter element <NUM> may be used in the filter apparatus <NUM> described herein.

As shown in <FIG> and <FIG>, the filter elements <NUM> according to the present embodiment each comprise inner filter cells 30IN and outer filter cells 30OUT; the outer filter cells 30OUT being disposed radially outside the inner filter cells 30IN. The filter elements <NUM> comprise a plurality of external ribs <NUM> extending radially outwardly from the cylindrical wall <NUM>. The external ribs <NUM> are arranged to form a series of filter channels <NUM> which are open along their length and may also perform mechanical filtration when the filter elements <NUM> form the filter pack <NUM>. As shown in <FIG>, the filter elements in the present embodiment have an external width of approximately <NUM> and a length of approximately <NUM>. The diameter of the cylindrical wall <NUM> is approximately <NUM>. The inner filter cells 30IN have a square profile measuring <NUM> x <NUM>; and the outer filter cells 30OUT have a major width of <NUM> and a minor width of <NUM>. The inner and outer filter cells 30IN, 30OUT in the present embodiment each have a cross-sectional area less than <NUM><NUM>.

The mechanical filter apparatus <NUM> comprises flow control means for controlling the supply of unfiltered water W from the aquaria <NUM> to the filter chamber <NUM>; and the return of filtered water W from the filter chamber <NUM> to the aquaria <NUM>. In the present embodiment, the flow control means comprises a liquid supply valve <NUM> and a liquid return valve <NUM>. The liquid supply valve <NUM> is operative to open and close the liquid supply conduit <NUM> to control the supply of unfiltered water W to the filter chamber <NUM>. The liquid return valve <NUM> is operative to open and close the liquid return conduit <NUM> to control the return of filtered water W to the aquaria <NUM>. The liquid supply valve <NUM> and the liquid return valve <NUM> can both be closed at least substantially to seal the filter chamber <NUM>. A liquid supply valve actuator <NUM>, for example a second electromechanical actuator, is provided for actuating the liquid supply valve <NUM>. A liquid return valve actuator <NUM>, for example a third electromechanical actuator, is provided for actuating the liquid return valve <NUM>. In alternative embodiments, the liquid supply valve <NUM> and/or the liquid return valve <NUM> may be operated manually. In alternate embodiments the flow control means may comprise a control valve for controlling the flow of liquid through the liquid supply conduit <NUM> and the liquid return conduit <NUM>. The control valve may be a multi-port valve, for example a <NUM>-way valve. The control valve could be configured also to control operation of the drain valve <NUM>.

As shown schematically in <FIG>, the mechanical filter apparatus <NUM> comprises an electronic control unit (ECU) <NUM> for controlling operation of the pump <NUM>, the drain valve <NUM>, the liquid supply valve <NUM> and the liquid return valve <NUM>. The ECU <NUM> comprises a processor <NUM> and a memory <NUM>. The processor <NUM> is configured to control operation of the drain valve actuator <NUM>, the liquid supply valve actuator <NUM> and the liquid return valve actuator <NUM>. The ECU <NUM> may thereby configure the mechanical filter apparatus <NUM> to perform either filtration or backwashing. In the present embodiment the ECU <NUM> implements a timer to control switching between filtration and backwashing. The time between backwashing cycles may, for example, be user-configurable. Other control strategies could be used to initiate backwashing, for example in dependence on a detected change in the load on the pump <NUM>. The ECU <NUM> may optionally also control operation of the check valve <NUM> to open and close the air supply conduit <NUM>. The ECU <NUM> may optionally be configured to implement a failsafe control strategy whereby operation of the pump <NUM> is inhibited when the drain valve <NUM> is open. The failsafe control strategy may avoid accidental draining of the water in the aquaria <NUM> by continuing to operate the pump <NUM> when the drain valve <NUM> is open.

Alternatively, or in addition, a water level sensor may be provided to output a level signal to the ECU <NUM> to indicate a level of the water in the filter chamber <NUM>. The level signal may provide an indication that the water in the filter chamber <NUM> is at or below a predetermined level, for example to indicate that backwashing is complete. The ECU <NUM> may be configured to close the drain valve <NUM> when the level signal indicates that the water level is at or below the predetermined level. The ECU <NUM> may control switching between backwashing and filtration in dependence on the level signal received from the water level sensor.

The operation of the mechanical filter apparatus <NUM> will now be described with reference to <FIG>. The mechanical filter apparatus <NUM> is illustrated in <FIG> filtering the water W from the aquaria <NUM>. To perform filtration, the ECU <NUM> controls the liquid supply valve actuator <NUM> to open the liquid supply valve <NUM>; and the liquid return valve actuator <NUM> to open the liquid return valve <NUM>. The ECU <NUM> activates the pump <NUM> to supply unfiltered water W from the aquaria <NUM> to the filter chamber <NUM>. The ECU <NUM> also controls the drain valve actuator <NUM> to close the drain valve <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 aquaria <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>, within the open filter cells <NUM> of each filter element <NUM> and within the filter channels <NUM>. The outlet mesh <NUM> prevents the filter elements <NUM> entering the liquid return conduit <NUM>.

As shown in <FIG>, the mechanical filter apparatus <NUM> is periodically backwashed to dislodge filtered material and to clean the filter elements <NUM>. To perform backwashing, the ECU <NUM> deactivates the pump <NUM>; controls the liquid supply valve actuator <NUM> to close the liquid supply valve <NUM>; and controls the liquid return valve actuator <NUM> to close the liquid return valve <NUM>. The filter chamber <NUM> is thereby sealed and the supply of water W inhibited. The ECU <NUM> then controls the drain valve actuator <NUM> to open the drain valve <NUM> to allow the water W in the filter chamber <NUM> to exit through the drain conduit <NUM> and to flush filtered particulates from the mechanical filter apparatus <NUM>. 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 <FIG>, 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 the filter channels <NUM>. 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>. Since the filter chamber <NUM> has a substantially continuous section, the agitation of the filter elements <NUM> is more uniform throughout backwashing than prior art systems incorporating a constriction into the sidewall of the filter chamber. 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 <FIG>, when the filter chamber <NUM> is completely drained, the filter elements <NUM> settle at the bottom of the filter chamber <NUM>. The inlet 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 ECU <NUM> controls the liquid supply valve <NUM> to open the liquid supply conduit <NUM>; and the liquid return valve <NUM> to open the liquid return conduit <NUM>. 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 after opening the liquid supply valve <NUM> such that additional washing of the filter elements <NUM> may be performed and the water flushed directly to waste through the drain conduit <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>.

When backwashing is complete, the liquid supply valve <NUM> is operated to open the liquid supply conduit <NUM>; and the liquid return valve <NUM> is operated to open the liquid return conduit <NUM>. The pump <NUM> is re-started to pump water from the aquaria <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 filtered water W is returned to the aquaria <NUM> through the liquid return conduit <NUM>. In a modified embodiment, after backwashing, the ECU <NUM> may be configured to control the pump <NUM> to gradually increase the speed of the water W supplied to the filter chamber <NUM>. The speed of the water W may be increased in steps or as a continuous curve (such as a logarithmic curve). By increasing the speed of the water W gradually, the uniformity of the filter pack formed by the filter elements <NUM> may be more improved.

The ECU <NUM> allows the filtration and backwashing of the filter elements <NUM> to be partially or completely automated. The ECU <NUM> may, for example, implement a timer circuit for controlling filtration and backwashing. The timer circuit may be user-configurable, for example to enable a user to specify backwashing frequency. At least in certain embodiments the air introducing means <NUM> provides an effective mechanism for agitating the filter elements <NUM>. The combination of the air introducing means <NUM> and the open cell filter elements <NUM> is believed to be particularly advantageous as some of the air bubbles B may dislodge material trapped within the filter cells <NUM>. Furthermore, at least in certain embodiments, the open cell structure may reduce the mass of the filter elements <NUM> and allow them to be agitated more readily by the air bubbles. This is particularly advantageous as the filter chamber <NUM> can be formed with a substantially uniform cross-section. In the present embodiment, the filter housing <NUM> comprises a tubular member <NUM> in the form of a right circular cylinder to form the filter chamber <NUM>. Thus, the filter housing <NUM> is formed without constrictions or narrowing sections intended to promote agitation of the filter elements <NUM> during backwashing.

By way of example, the mechanical filter apparatus <NUM> in accordance with the present invention may comprise a tubular member <NUM> having a diameter of approximately <NUM> and a vertical height of approximately <NUM>. The filter chamber <NUM> formed in said tubular member <NUM> may have a volume of approximately eight (<NUM>) litres. In use, the filter chamber may contain approximately six (<NUM>) litres of water W and approximately two (<NUM>) litres by volume of said filter elements <NUM>. The volume of the filter chamber <NUM> is proportional to the volume of liquid that can be filtered by the mechanical filter apparatus <NUM>. It has been determined that the volume of the filter chamber <NUM> may correspond to the total volume of liquid to be filtered divided by a predefined numerical value n. The predefined numerical value n is typically in the range forty-five (<NUM>) to fifty-five (<NUM>) inclusive and in the present embodiment is fifty (<NUM>). Thus, the mechanical filter apparatus <NUM> according to the present exemplary embodiment can be used to filter approximately <NUM> litres (n*filter chamber volume) of water. The combined volume of the water in the aquaria <NUM> in the present embodiment should be approximately <NUM> litres. In use, a flow rate per unit cross-sectional area of the static filter pack in the filter chamber <NUM> should be in the range <NUM><NUM>/m<NUM>/h to <NUM><NUM>/m<NUM>/h. In the present embodiment, the flow rate through the mechanical filter apparatus <NUM> is approximately <NUM> litres/hour (<NUM><NUM>/h). The flow rate per unit cross-sectional area of the static filter pack is therefore approximately <NUM><NUM>/m<NUM>/h. It will be understood that the dimensions of the mechanical filter apparatus <NUM> and/or the flow rate per unit cross-sectional area may be modified in alternate embodiments.

In use, the mechanical filter apparatus <NUM> is periodically backwashed. During backwashing, the water W in the filter chamber <NUM> is drained through the drain valve <NUM>. In the present exemplary embodiment, each backwashing operation results in approximately <NUM> litres of the water W being drained. Fresh water is subsequently introduced into the filter system S to refill the filter chamber <NUM>, thereby maintaining the water level in the aquaria <NUM>. It will be appreciated that each backwashing operation and the associated refilling of the filter chamber <NUM> results in a proportion of the water W in the aquaria <NUM> being replaced. A weekly target of replacing <NUM>-<NUM>% by volume of the water W in the aquaria <NUM> has been determined as appropriate for preserving water quality for fish and other aquatic animals. In the present embodiment, this corresponds to replacing between <NUM> and <NUM> litres of water each week. As approximately <NUM> litres is drained from the filter chamber <NUM> during each backwashing operation, this corresponds to between seven (<NUM>) and eleven (<NUM>) backwashing operations each week. The filter system S may, for example, be configured to backwash the mechanical filter apparatus <NUM> ten (<NUM>) times each week. The ECU <NUM> may be configured to implement a backwashing schedule determined using this technique. Other backwashing schedules may be implemented.

In alternative embodiments of the present invention, the tubular member <NUM> may taper outwardly towards its base, for example to form a truncated cone or pyramid. This arrangement would provide additional space for the filter elements <NUM> to move within the filter chamber <NUM> as the water W drains through the drain conduit <NUM>. It is believed that this may increase the movement of the filter elements <NUM> and promote cleaning during backwashing. At least in certain embodiments the tubular member <NUM> may comprise a substantially continuous taper along said longitudinal axis X1-X1 (i.e. free from step changes in its cross-section).

The above embodiment of the mechanical filter apparatus <NUM> is configured to establish an up flow of water through the filter chamber <NUM> during filtration. It will be appreciated that the mechanical filter apparatus <NUM> could be configured to generate a down flow of water through the filter chamber <NUM> during filtration. In particular, the relative positioning of the liquid inlet <NUM> and the liquid outlet <NUM> would be reversed such that the liquid inlet <NUM> is disposed in an upper portion of the filter chamber <NUM> and the liquid outlet <NUM> is disposed in a lower portion of the filter chamber <NUM>. The filter elements <NUM> may have neutral buoyancy or negative buoyancy in the water W. During filtration, the filter pack <NUM> would form at the bottom of the filter chamber <NUM>. During backwashing, the air introducing means <NUM> would introduce air into the bottom of the filter chamber <NUM> to agitate the filter elements <NUM> and break up the filter pack <NUM>. The filter housing <NUM> may comprise a tubular member <NUM> to form the filter chamber <NUM>. The tubular member <NUM> may have a substantially uniform cross profile along its longitudinal axis X-X. The tubular member <NUM> may, for example, have a circular cross profile (i.e. a right circular cylinder). Again, the filter housing <NUM> may be formed without constrictions or narrowing sections intended to promote agitation of the filter elements <NUM> during backwashing. In a variant, the filter elements <NUM> may have positive buoyancy and, due to the increased flow speed of the water W, the static filter pack may still form in the filter chamber <NUM>.

A filter system S incorporating a mechanical filter apparatus <NUM> in accordance with a further embodiment of the present invention will now be described with reference to <FIG> and <FIG>. The filter system S is a modified version of the embodiment described herein with reference to <FIG>. Like reference numerals are used for like components.

As shown schematically in <FIG>, the filter system S according to the present embodiment is configured to filter the water W in a swimming pool <NUM>. A pump <NUM> is provided for pumping unfiltered water W from the swimming pool <NUM> to the mechanical filter apparatus <NUM>. The water W is mechanically filtered and the filtered water W returned to the swimming pool <NUM>. The filter water W is returned to the swimming pool <NUM> through a liquid return conduit <NUM> having an outlet disposed above the level of the water in the swimming pool <NUM>. The pump <NUM> may be incorporated into the mechanical filter apparatus <NUM>.

As shown in <FIG>, the mechanical filter apparatus <NUM> comprises a filter housing <NUM> which defines a filter chamber <NUM> having a sidewall <NUM>. The filter chamber <NUM> is a sealed chamber capable of supporting an operating pressure greater than atmospheric pressure. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> and collectively form a mechanical filter. The filter elements <NUM> have an open-cell structure. By way of example, the mechanical filter apparatus <NUM> may comprise filter elements <NUM> of the type described herein with reference to <FIG>, <FIG>, <FIG>. As described herein, the mechanical filter apparatus <NUM> is operable to filter the water W; and to backwash the filter elements <NUM> to remove filtered material. 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>. 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>. 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 mechanical filter apparatus <NUM> 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 mechanical filter apparatus <NUM> 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>. In the present embodiment, an outlet of the liquid return conduit <NUM> is located above the level of the water W in 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>. In the present embodiment, there is an up flow of water W through the filter chamber <NUM> during filtration, as illustrated in <FIG>. 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 mechanical 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. In the present embodiment, the drain conduit <NUM> is connected to the liquid supply conduit <NUM> such that the filter chamber <NUM> is drained through the liquid inlet <NUM>. In alternative embodiments, a separate drain outlet may be provided, for example at the bottom of the filter chamber <NUM>. A drain valve <NUM> is provided for selectively opening and closing the drain conduit <NUM>. The drain valve <NUM> could be manually operated, for example by operating a control lever. In the present embodiment, the drain valve <NUM> is actuated by a drain valve actuator <NUM>, for example a first electromechanical actuator, such as a solenoid. A lower mesh <NUM> and an upper mesh <NUM> are provided to retain the filter elements <NUM> in the filter chamber <NUM>.

The mechanical filter apparatus <NUM> comprises means for introducing air into the filter chamber <NUM> to perform backwashing. The air introduction means (denoted generally by the reference numeral <NUM>) comprises an air supply conduit <NUM>. The configuration of the air introducing means <NUM> in the present embodiment differs from that of the previous embodiment. In particular, the air supply conduit <NUM> is fluidly connected to the liquid return conduit <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> has an air intake <NUM> which is in fluid communication with the liquid return conduit <NUM>. During backwashing of the mechanical filter apparatus <NUM> the air supply conduit <NUM> draws air through the liquid return conduit <NUM> which is open to atmosphere. The advantage of this arrangement is that the possibility of a leak occurring through the air supply conduit <NUM> is reduced since any liquid pumped through the air supply conduit <NUM> would be returned to the swimming pool <NUM> through the liquid return conduit <NUM>. The air inlet <NUM> is formed in a sidewall of the filter chamber <NUM>. The vertical offset between the air inlet <NUM> and the drain conduit <NUM> establishes a pressure differential which enables air to be drawn into the filter chamber <NUM> during backwashing. Thus, the air inlet <NUM> is disposed on the sidewall at a height above the height of the bottom of the drain conduit <NUM>. By establishing a pressure differential, air is introduced into the filter chamber <NUM> when the drain valve <NUM> is open to perform backwashing. The height of the air inlet <NUM> may be adjusted to alter this pressure differential, thereby controlling the rate at which air is introduced into the filter chamber <NUM> during backwashing. In a variant, the air inlet <NUM> may comprise an adjustable height outlet nozzle. The outlet nozzle may comprise a telescopic conduit; or may be rotatable about a horizontal axis to adjust the height of the air inlet <NUM>. By adjusting the height of the outlet nozzle, the pressure differential may be altered to controllably adjust the rate at which air is drawn into the filter chamber.

In the present embodiment, the control valve for the air supply conduit <NUM> may be omitted. Rather, the air supply conduit <NUM> may be connected directly to the liquid return conduit <NUM>. Although a portion of the water W may pass through the air supply conduit <NUM>, this has little or no effect on filtration since the water W is circulated through the filter chamber <NUM> multiple times (performing multi-pass filtration). A control valve (not shown) or a flow restrictor may optionally be disposed in the air supply conduit <NUM>. The control valve may be configured to allow air to pass through the air supply conduit <NUM> during backwashing; and to prevent water exiting the filtering chamber <NUM> through the air supply conduit <NUM> during filtration. The control valve may be in the form of a one-way (check) valve. The control valve 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>. Alternatively, the control valve may comprise a needle valve for controlling the air intake. The control valve may, for example, comprise a ball for locating in a valve seat to seal the air supply conduit <NUM>. In an alternative embodiment, the control valve may be replaced with a valve member which may be selectively opened and closed. In alternative embodiments, the control valve may comprise an electromechanical actuator, such as a solenoid, for opening and closing the air supply conduit <NUM>. In a modified arrangement, a three-way valve (not shown) may be provided selectively to connect either the filter chamber <NUM> or the air supply conduit <NUM> to the liquid return conduit <NUM>. This implementation of a three-way valve may be used in one or more of the embodiments described herein.

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.

The mechanical filter apparatus <NUM> comprises flow control means for controlling the supply of unfiltered water W from the swimming pool <NUM> to the filter chamber <NUM>; and the return of filtered water W from the filter chamber <NUM> to the swimming pool <NUM>. The flow control means comprises a liquid supply valve <NUM> and a liquid return valve <NUM>. The liquid supply valve <NUM> is operative to open and close the liquid supply conduit <NUM> to control the supply of unfiltered water W to the filter chamber <NUM>. The liquid supply valve <NUM> is a one-way (check) valve adapted to allow liquid to be introduced into the filter chamber <NUM>. The liquid return valve <NUM> is a one-way (check) valve adapted to allow liquid to be introduced into the filter chamber <NUM>. The liquid supply valve <NUM> and the liquid return valve <NUM> can both be closed at least substantially to seal the filter chamber <NUM>. In a modified arrangement, the liquid supply valve <NUM> and/or the liquid return valve <NUM> comprise an electromechanical actuator.

As shown schematically in <FIG>, the mechanical filter apparatus <NUM> comprises an electronic control unit (ECU) <NUM> for controlling operation of the pump <NUM> and the drain valve <NUM>. The ECU <NUM> comprises a processor <NUM> and a memory <NUM>. The operation of the ECU <NUM> is substantially unchanged from the previous embodiment. As the water W is drained from the filter chamber <NUM>, the water in the liquid return conduit <NUM> is initially drawn back into the filter chamber <NUM> through the air supply conduit <NUM> and then drained through the drain conduit <NUM>. Once the water has drained from the liquid return conduit <NUM>, air is drawn through the liquid return conduit <NUM> and introduced into the filter chamber <NUM> through the air supply conduit <NUM>. The introduction of air into the filter chamber <NUM> agitates the filter elements <NUM> and performs cleaning. The backwashing of the filter elements <NUM> is substantially the same as the previous embodiment.

The air supply conduit <NUM> is illustrated in <FIG> as being external to the filter chamber <NUM>. In a modified arrangement, the air supply conduit <NUM> may extend vertically within the filter chamber <NUM>. The air supply conduit <NUM> could, for example, be mounted to the upper closure member <NUM>. The internal positioning of the air supply conduit <NUM> could be applied to the other embodiments described herein. The air supply conduit <NUM> may form said one or more air inlet <NUM>, for example at an open end thereof. The air supply conduit <NUM> may be movably mounted such that the vertical position of the one or more air inlets <NUM> may be adjusted within the filter chamber <NUM>. By changing the vertical height of the one or more air inlets <NUM>, the pressure differential between the drain outlet and the air inlet <NUM> can be adjusted, thereby changing the rate at which air is introduced into the filter chamber <NUM> during backwashing. Adjustable fixing means could be provided on the upper closure member <NUM> for adjustably fixing the vertical position of the air supply conduit <NUM>.

A further embodiment of the mechanical filter apparatus <NUM> in accordance with an aspect of the present invention is shown in <FIG>. The mechanical filter apparatus <NUM> is a modified version of the embodiment described herein with reference to <FIG> and <FIG>. Like reference numerals are used for like components. The mechanical filter apparatus <NUM> according to the present embodiment may be incorporated into the filter system S shown in <FIG>, for example.

As described herein, there is a down flow of water W through the filter chamber <NUM> during filtration, as illustrated in <FIG>. The unfiltered water W is introduced through a liquid inlet <NUM> at the top of the filter chamber <NUM>; and the filtered water W exits through a liquid outlet <NUM> at the bottom of the filter chamber <NUM>. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> and collectively form a mechanical filter. The filter elements <NUM> have an open-cell structure. By way of example, the mechanical filter apparatus <NUM> may comprise filter elements <NUM> of the type described herein with reference to <FIG>, <FIG>, <FIG>.

The mechanical filter apparatus <NUM> comprises a liquid supply conduit <NUM> for supplying unfiltered water from the swimming pool <NUM> to the liquid inlet <NUM> formed in the filter chamber <NUM>. The mechanical filter apparatus <NUM> also comprises a liquid return conduit <NUM> for returning filtered water from the liquid outlet <NUM> formed in the filter chamber <NUM> to the swimming pool <NUM>. The liquid inlet <NUM> is formed in the upper closure member <NUM> and the liquid outlet <NUM> is formed in the lower closure member <NUM>. During filtration, there is a down flow of water W through the filter chamber <NUM>, as illustrated in <FIG>. The unfiltered water W is introduced through the liquid inlet <NUM> at the top of the filter chamber <NUM>; and the filtered water W exits through the liquid outlet <NUM> at the bottom 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 mechanical filter apparatus <NUM> comprises means for introducing air into the filter chamber <NUM> to perform backwashing. The air introduction means (denoted generally by the reference numeral <NUM>) comprises an air supply conduit <NUM>. The configuration of the air introducing means <NUM> is unchanged from the previous embodiment. The air supply conduit <NUM> has an air intake <NUM> which is fluidly connected to the liquid return conduit <NUM>. During backwashing of the mechanical filter apparatus <NUM> the air supply conduit <NUM> draws air through the liquid return conduit <NUM> which has an outlet disposed above the level of the water in the swimming pool <NUM> and is, therefore, open to atmosphere. The air inlet <NUM> is formed in a sidewall of the filter chamber <NUM>. The air inlet <NUM> is disposed on the sidewall at a height above the height of drain conduit <NUM> in order to establish a pressure differential. By establishing a pressure differential, air is introduced into the filter chamber <NUM> when the drain valve <NUM> is open to perform backwashing.

A further embodiment of the mechanical filter apparatus <NUM> in accordance with an aspect of the present invention is shown in <FIG> and <FIG>. The mechanical filter apparatus <NUM> is a modified version of the embodiment described herein with reference to <FIG> and <FIG>. Like reference numerals are used for like components. The mechanical filter apparatus <NUM> according to the present embodiment may be incorporated into the filter system S shown in <FIG>, for example.

The mechanical filter apparatus <NUM> comprises a liquid supply conduit <NUM> for supplying unfiltered water from a swimming pool <NUM> to a liquid inlet <NUM>. Flow control means is provided for controlling the supply of liquid to the filter chamber <NUM>. The flow control means comprises a liquid supply valve <NUM> in the present embodiment. An electromechanical actuator may be provided for controlling operation of the liquid supply valve <NUM>. A liquid return conduit <NUM> is provided for returning filtered water from a liquid outlet <NUM> to the swimming pool <NUM>. The filter water W is returned to the swimming pool <NUM> through a liquid return conduit <NUM> having an outlet disposed above the level of the water in the swimming pool <NUM>. A drain valve <NUM> is provided for controlling drainage of the filter chamber <NUM> through a drain conduit <NUM>. An electromechanical actuator may be provided for controllably opening and closing the drain valve <NUM>. As illustrated in <FIG>, a liquid inlet <NUM> is disposed at the top of the filter chamber <NUM> for introducing water from the swimming pool <NUM>. In the illustrated arrangement, the liquid inlet <NUM> is provided in a side wall of the filter chamber <NUM>, but could be provided in the upper closure member <NUM>. The liquid supply valve <NUM> and/or the drain valve <NUM> may be controlled by an ECU (not shown) to provide automated operation of the mechanical filter apparatus <NUM>. Alternatively, the liquid supply valve <NUM> and/or the drain valve <NUM> may be manually operated.

In the present embodiment, the flow of water W follows a serpentine path through the filter chamber <NUM> during filtration. The unfiltered water W enters the filter chamber <NUM> through the liquid inlet <NUM> and travels downwardly through the filter chamber <NUM>. The flow direction of the water W in the filter chamber <NUM> is reversed at or proximal to the bottom of the filter chamber <NUM> and the water W then flows upwardly through an internal conduit 45disposed in the filter chamber <NUM>. The internal conduit <NUM> performs the dual function of operating as an air inlet conduit during backwashing (corresponding to the air supply conduit <NUM> of the other embodiments described herein); and a liquid outlet conduit during filtration (corresponding to a section of the liquid return conduit <NUM>). The internal conduit <NUM> in the present embodiment extends substantially vertically downwardly from a liquid outlet <NUM> disposed at the top of the filter chamber <NUM>. The internal conduit <NUM> is disposed centrally in the filter chamber <NUM> coincident with a longitudinal axis X-X of the filter chamber <NUM>. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> and collectively form a mechanical filter in an annular region of the filter chamber <NUM> around the internal conduit <NUM>. The filter elements <NUM> have an open-cell structure. By way of example, the mechanical filter apparatus <NUM> may comprise filter elements <NUM> of the type described herein with reference to <FIG>, <FIG>, <FIG>. 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 vertical position of the air inlets <NUM> may be adjusted to alter the pressure differential between the drainage outlet and the air intake. For example, the vertical position of the internal conduit <NUM> may be adjustable.

In the present embodiment, the means for introducing air into the filter chamber <NUM> (denoted generally by the reference numeral <NUM>) comprises the internal conduit <NUM>. As shown in <FIG>, the internal conduit <NUM> has an air intake <NUM> which is connected to the liquid return conduit <NUM> at the top of the filter chamber <NUM>; and an air inlet <NUM> disposed at the bottom of the filter chamber <NUM>. A guard or mesh is provided over the air inlet <NUM> to prevent the filter elements <NUM> escaping through the internal conduit <NUM>. In the present embodiment, the internal conduit <NUM> extends downwardly through the lower mesh <NUM>. During backwashing of the mechanical filter apparatus <NUM> the internal conduit <NUM> draws air through the liquid return conduit <NUM> which has an outlet above the level of the water in the swimming pool <NUM> and is, therefore, open to atmosphere. In this arrangement, the liquid return valve provided in the liquid return conduit <NUM> is optional. In a modified arrangement, a separate air inlet may be provided in the liquid return conduit <NUM>. An air supply valve (not shown), for example comprising a one-way (check) valve, may be provided for controlling the supply of air during backwashing. If the outlet from the liquid return conduit <NUM> is disposed below the level of the water in the swimming pool <NUM>, it will be understood that a separate air inlet should be provided, for example at the top of the internal conduit <NUM> or in the liquid return conduit <NUM>.

In alternative embodiments of the present invention, the tubular member <NUM> may taper inwardly towards its base, for example to form an inverted truncated cone or pyramid. This arrangement would provide additional space for the filter elements <NUM> to move within the filter chamber <NUM> when air is initially introduced into the filter chamber <NUM> to break up the filter pack <NUM>, It is believed that this may increase the movement of the filter elements <NUM> and promote cleaning during backwashing. At least in certain embodiments the tubular member <NUM> may comprise a substantially continuous taper along said longitudinal axis X-X (i.e. free from step changes in its cross-section).

A further embodiment of the mechanical filter apparatus <NUM> will now be described with reference to <FIG> and <FIG>. Like reference numerals are used for like components in the description of this arrangement.

As shown in <FIG>, the mechanical filter apparatus <NUM> comprises a filter housing <NUM>, a first conduit <NUM>, a second conduit <NUM> and a control valve <NUM>. The filter housing <NUM> defines a filter chamber <NUM> containing a plurality of said mechanical filter elements <NUM> which form the static filter pack <NUM>. In the present embodiment, the filter chamber <NUM> is at least substantially sealed. The mechanical filter apparatus <NUM> is configured such that unfiltered water from the swimming pool <NUM> is pumped into the filter chamber <NUM> through the second conduit <NUM> and exits through the first conduit <NUM>. The general upwards flow of water through the filter chamber <NUM> is illustrated in <FIG> by a series of arrows. The mechanical filter elements <NUM> in the present embodiment have substantially neutral buoyancy or positive buoyancy in water.

As described herein, the mechanical filter apparatus <NUM> can comprise agitating means for agitating the mechanical filter elements <NUM>. The mechanical filter apparatus <NUM> according to the present embodiment comprises means for introducing air into the filter chamber <NUM> to break up or disrupt the mechanical filter elements <NUM> forming the static filter pack <NUM>. The air introduction means (denoted generally by the reference numeral <NUM>) comprises an air supply conduit <NUM>, a supply manifold <NUM> and a one-way valve <NUM>. The air supply conduit <NUM> has an intake through which air can be drawn into the filter chamber <NUM>. The one-way valve <NUM> is disposed in the air supply conduit <NUM> proximal to the inlet. The supply manifold <NUM> comprises a central chamber <NUM> and a plurality of distribution conduits <NUM>. The central chamber <NUM> is in fluid communication with the air supply conduit <NUM> via the second conduit <NUM>. The distribution conduits <NUM> extend radially outwardly from the central chamber <NUM> and are disposed at, or proximal to the base of the filter chamber <NUM>. The distribution conduits <NUM> each have a plurality of air inlet apertures <NUM> for introducing air into the filter chamber <NUM>. The air supply conduit <NUM> in the present embodiment is connected to the second conduit <NUM> via the control valve <NUM>. The one-way 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 one-way valve <NUM> may, for example, comprise a spring-biased closure member. In an alternative embodiment, the one-way valve <NUM> may be replaced with a two-way valve which may be selectively opened and closed.

The control valve <NUM> is configured such that, during filtration, the first conduit <NUM> is connected to a return conduit <NUM>; and the second conduit <NUM> is connected to a supply conduit <NUM>. The second conduit <NUM> is operative to supply unfiltered water from the swimming pool <NUM>; and the first conduit <NUM> returns filtered water to the swimming pool <NUM>. Furthermore, the control valve <NUM> is configured such that, during backwashing, the first conduit <NUM> is closed; and the second conduit <NUM> is connected to the air supply conduit <NUM>. The housing <NUM> comprises a drainage port <NUM> disposed at the base of the filter chamber <NUM>. In the present embodiment, the drainage port <NUM> is connected to the waste drain conduit <NUM> and is opened during backwashing. The control valve <NUM> may be configured to control the opening and closing of the drainage port <NUM>. However, in the present embodiment, a separate drainage valve <NUM> is provided for opening and closing the drainage port <NUM>. The drainage valve <NUM> is operated manually in the present embodiment. In alternate embodiments, the drainage valve <NUM> could comprise an actuator, such as a solenoid, to provide automated or partially-automated backwashing. A mesh <NUM> is provided over the drainage port <NUM> to prevent the mechanical filter elements <NUM> entering the waste drain conduit <NUM> when the drainage valve <NUM> is open. The mesh <NUM> may be configured to control the flow of water from the filter chamber <NUM> during backwashing, for example in dependence on the size and/or number of holes in the mesh <NUM>.

As shown in <FIG>, when the mechanical filter apparatus <NUM> is performing filtration, the water is pumped from the swimming pool <NUM> by the pump <NUM> into the filter housing <NUM>. The pumped water is introduced into the filter chamber <NUM> through the second conduit <NUM>. The unfiltered water enters the filter housing <NUM> through the distribution conduits <NUM> of the supply manifold <NUM>. The water flows upwardly through the filter chamber <NUM> and exits through the first conduit <NUM>. It will be understood that an up-flow of water is established through the filter chamber <NUM> during filtration. The upwards movement of the water displaces the mechanical filter elements <NUM> upwardly such that the static filter pack <NUM> is formed at the top of the filter chamber <NUM>.

As shown in <FIG>, when the mechanical filter apparatus <NUM> is performing backwashing, the pump <NUM> is stopped to inhibit the supply of water from the swimming pool <NUM> to the filter housing <NUM>. The control valve <NUM> is operated to close the first conduit <NUM> and to connect the second conduit <NUM> to the air supply conduit <NUM>. The drainage valve <NUM> is then opened to allow the water in the filter housing <NUM> to flow through the drainage port <NUM> into the waste drain conduit <NUM>. Since the filter housing <NUM> is sealed, the flow of water out of the filter chamber <NUM> reduces the pressure within the filter housing <NUM> causing the one-way valve <NUM> to open allowing air to be drawn into the air supply conduit <NUM>. By draining water from the sealed filter chamber <NUM>, the operating pressure drops below atmospheric pressure, thereby drawing air into the filter chamber <NUM> through the air supply conduit <NUM>. The air enters the central chamber <NUM> and is drawn through into the distribution conduits <NUM>. The air is then introduced into the filter chamber <NUM> through the air inlet apertures <NUM> formed in the distribution conduits <NUM>. The resulting air bubbles travel upwardly through the water in the filter chamber <NUM> and disrupt the suspended mechanical filter elements <NUM>. The mechanical filter elements <NUM> are agitated by the air bubbles and the static filter pack <NUM> is broken up. It will be appreciated that the water in the filter chamber <NUM> continues to drain through the drainage port <NUM>, such that the level of the water continues to drop causing further agitation of the mechanical filter elements <NUM> within the filter chamber <NUM>. It will be understood that, by agitating the mechanical filter elements <NUM>, material and debris filtered by the mechanical filter elements <NUM> is dislodged and returned to the water within the filter chamber <NUM>. The agitation of the mechanical filter elements <NUM> continues until the water level in the filter chamber <NUM> drops below the position of the air inlet apertures <NUM> formed in the distribution conduit <NUM>. The introduction of air into the filter chamber <NUM> continues concurrently with drainage of the water from the filter chamber <NUM>. By draining the water through the waste drain conduit <NUM>, the material and debris is expelled from the filter chamber <NUM>. The mechanical filter elements <NUM> may thereby be cleaned ready to perform additional filtration. The pressure in the filter chamber <NUM> returns to atmospheric pressure and the one-way valve <NUM> closes.

When the filter chamber <NUM> is empty, the control valve <NUM> is operated to open the second conduit <NUM> and the pump35 re-started. The control valve <NUM> can be operated to open the first conduit <NUM>. The drainage valve <NUM> is operated to close the drainage port <NUM> partially or completely to refill the filter chamber <NUM> with water from the swimming pool <NUM>. The drainage valve <NUM> may be closed after opening the second conduit <NUM> to perform additional washing of the mechanical filter elements <NUM> and optionally to flush the second conduit <NUM>. In alternative arrangements, the drainage valve <NUM> may be closed before or concurrent with opening of the second 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 second conduit <NUM> closed and the drainage valve <NUM> re-opened. It will be understood that the drainage valve <NUM> may be incorporated into the control valve <NUM>.

When backwashing is complete, the control valve <NUM> is operated to open the first and second conduits <NUM>, <NUM>. The pump <NUM> is re-started to pump water from the swimming pool <NUM> to the filter housing <NUM>. The drainage valve <NUM> is operated to close the drainage port <NUM> and the filter chamber <NUM> is refilled with water from the swimming pool <NUM>. The mechanical filter elements <NUM> re-form the static filter pack <NUM> and are operative to perform mechanical filtration of the water.

The air introduction means <NUM> described with reference to the present embodiment is a passive system insofar as it relies on the water draining from the filter chamber <NUM> to draw air through the air supply conduit <NUM>. Alternatively, or in addition, an air pump may be provided actively to pump air through the air supply conduit <NUM>.

The mechanical filter apparatus <NUM> shown in <FIG> can be implemented by modifying a conventional swimming pool filter apparatus, such as a sand bed filter. According to further aspects of the present invention, there is provided a conversion kit for converting an existing swimming pool filter apparatus; and a method of converting an existing swimming pool filter apparatus.

It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the appended claims. The present invention has been described with reference to mechanically filtering the water W in one or more aquaria or swimming pool <NUM>.

At least some of the air inlets <NUM> may be sized to form bubbles of air which may enter the filter cells <NUM> formed within the filter elements <NUM> to dislodge trapped material. Some of the air inlets <NUM> may be larger to promote agitation of the filter elements <NUM>, for example to break up the filter pack <NUM>. In certain embodiments, the air inlets <NUM> may be different sizes to promote formation of bubbles having different sizes.

It will be understood that other types of filtration, such as biological filtration, may be performed in addition to mechanical filtration. It is envisaged that any such biological filtration would be performed as a separate filtration stage, for example in a separate biological filtration chamber. However, under appropriate conditions, a biofilm may be allowed to develop on the filter elements <NUM>. In these scenarios, the filter elements <NUM> may also perform biological filtration of the water at the same time as mechanical filtration. The mechanical filter apparatus <NUM> may be used in combination with an ultra violet (UV) filter to clarify the water W.

A throttle or restriction may be provided in the air supply conduit <NUM> to control the introduction of air into the filter chamber <NUM>, for example to extend the time taken to drain the filter chamber <NUM> and to prolong backwashing. A control valve may be provided in the air supply conduit <NUM> for selectively controlling the introduction of air into the filter chamber <NUM>. The control valve may be adjustable to control the introduction of air during backwashing. The control valve could be manually operated. Alternatively, the control valve may comprise an electromechanical actuator, such as a solenoid or a servo. In certain embodiments, the control valve may be controlled by the ECU <NUM>.

In a variant of the embodiment described herein, the air supply conduit <NUM> may be arranged such that the air intake <NUM> is disposed at a position above the level of the water W in the filter chamber <NUM>. The height of the air intake <NUM> may optionally also be positioned in dependence on the maximum operating pressure generated in the filter chamber <NUM> by the pump <NUM>. In these arrangements, the check valve <NUM> could be omitted from the mechanical filter apparatus <NUM>.

The mechanical filter apparatus <NUM> has been described with reference to filtering water from several aquaria <NUM>. It will be understood that the mechanical filter apparatus <NUM> may be configured to filter the water from a single aquarium. Furthermore, at least certain embodiments of the present invention may have other applications, for example filtering the water in a swimming pool. Alternatively, or in addition, the filter apparatus may be suitable for filtering water in ponds, aqua-culture, swimming pools, swimming baths, swimming ponds, leisure pools, hot tubs, spas and leisure parks.

In the embodiment described herein, either the liquid supply conduit <NUM> or the liquid return conduit <NUM> opens into a lower portion of the filter chamber <NUM>. The mechanical filter apparatus <NUM> may be modified to utilise a profile of either the liquid supply conduit <NUM> or the return conduit <NUM> as part of the air introducing means <NUM> to supply air into the filter chamber <NUM>. The liquid supply valve <NUM> may, for example, be configured to connect the liquid supply conduit <NUM> to an air supply conduit <NUM> through which air may be drawn into filter chamber <NUM>.

The filter chamber <NUM> has been described herein as being in the form of a cylinder having a uniform circular cross-section along the longitudinal axis X-X. In alternative embodiments, the filter chamber <NUM> may have a substantially continuously tapered profile along said longitudinal axis X-X. The sidewall <NUM> may taper inwardly in an upwards direction, for example to form a truncated cone or a truncated pyramid. Alternatively, the sidewall <NUM> may taper inwardly in a downwards direction, for example to form an inverted truncated cone or an inverted truncated pyramid.

A further embodiment of the mechanical filter apparatus <NUM> is shown schematically in <FIG>. Like reference numerals are used for like components. In this arrangement, the filter chamber <NUM> consists of a substantially continuously tapered profile. The profile is tapered along the longitudinal axis X-X of the filter chamber <NUM>. In the present embodiment, the sidewall <NUM> is tapered inwardly in an upwards direction. Thus, the filter chamber <NUM> has a profile which is continuously tapered inwardly along the longitudinal axis X-X from a base to a top thereof. The filter chamber <NUM> has a substantially circular cross-section and forms a truncated cone. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> to perform mechanical filtration of the water W. The filter elements <NUM> form a filter pack <NUM> for performing mechanical filtration.

The mechanical filter apparatus <NUM> comprises a liquid supply conduit <NUM> for supplying unfiltered water to a liquid inlet <NUM> formed in the filter chamber <NUM>. The mechanical filter apparatus <NUM> also comprises a liquid return conduit <NUM> for returning filtered water W from a liquid outlet <NUM> formed in the filter chamber <NUM>. The liquid inlet <NUM> is disposed at the bottom of the filter chamber <NUM> and the liquid outlet <NUM> is disposed at the top of the filter chamber <NUM>. The water W flows upwardly through the filter chamber <NUM> from the liquid inlet <NUM> to the liquid outlet <NUM>. A liquid supply valve <NUM> is provided to open and close the liquid supply conduit <NUM>; and a liquid return valve <NUM> is provided to open and close the liquid return conduit <NUM>. The mechanical filter apparatus <NUM> comprises a drain conduit <NUM> and a drain valve <NUM>. In the present embodiment, the drain conduit <NUM> is connected to the liquid supply conduit <NUM>.

In the present embodiment, the filter elements <NUM> have substantially neutral buoyancy or positive buoyancy. The up flow of water W causes the filter elements <NUM> to form a filter pack <NUM> at the top of the filter chamber <NUM>. Air introducing means <NUM> is provided for introducing air into the filter chamber <NUM> during backwashing. The air introducing means <NUM> comprises an air supply conduit <NUM> and is configured to allow air to be drawn into the filter chamber <NUM> through a plurality of air inlets <NUM> as water W is drained from the filter chamber <NUM>.

The operation of the mechanical filter apparatus <NUM> to perform filtration and backwashing is unchanged from the embodiment described above. The mechanical filter apparatus <NUM> is illustrated performing filtration in <FIG>. During filtration, the tapered configuration of the filter chamber <NUM> helps to compact the filter elements <NUM> together as they are displaced upwardly by the up flow of water W through the filter chamber <NUM>. During backwashing, the water W is drained from the filter chamber <NUM> and the volume available for movement of the filter elements <NUM> increases as the level of the water W drops. The air introducing means <NUM> allows air to be drawn into the filter chamber <NUM> by the reduced pressure in the filter chamber <NUM> caused by the water W draining from the filter chamber <NUM>. The air enters the filter chamber <NUM> through the air inlets <NUM> and bubbles upwardly through the water W thereby promoting agitation of the filter elements <NUM>. At least in certain embodiments the tapered profile of the filter chamber <NUM> may facilitate filtration and backwashing.

A further embodiment of the mechanical filter apparatus <NUM> is shown schematically in <FIG>. Like reference numerals are used for like components. In this arrangement, the filter chamber <NUM> consists of a substantially continuously tapered profile. The profile is tapered along the longitudinal axis X-X of the filter chamber <NUM>. In the present embodiment, the sidewall <NUM> is tapered outwardly in an upwards direction. Thus, the filter chamber <NUM> has a profile which is continuously tapered outwardly along the longitudinal axis X-X from a base to a top thereof. The filter chamber <NUM> has a substantially circular cross-section and forms an inverted truncated cone. A plurality of filter elements <NUM> are disposed in the filter chamber <NUM> to perform mechanical filtration of the water W. The filter elements <NUM> form a filter pack <NUM> for performing mechanical filtration.

The mechanical filter apparatus <NUM> comprises a liquid supply conduit <NUM> for supplying unfiltered water to a liquid inlet <NUM> formed in the filter chamber <NUM>. The mechanical filter apparatus <NUM> also comprises a liquid return conduit <NUM> for returning filtered water W from a liquid outlet <NUM> formed in the filter chamber <NUM>. The liquid inlet <NUM> is disposed at the top of the filter chamber <NUM> and the liquid outlet <NUM> is disposed at the bottom of the filter chamber <NUM>. The water W flows downwardly through the filter chamber <NUM> from the liquid inlet <NUM> to the liquid outlet <NUM>. A liquid supply valve <NUM> is provided to open and close the liquid supply conduit <NUM>; and a liquid return valve <NUM> is provided to open and close the liquid return conduit <NUM>. The mechanical filter apparatus <NUM> comprises a drain conduit <NUM> and a drain valve <NUM>. In the present embodiment, the drain conduit <NUM> is connected to the liquid return conduit <NUM>.

In the present embodiment, the filter elements <NUM> have substantially neutral buoyancy or negative buoyancy. The down flow of water W causes the filter elements <NUM> to form a filter pack <NUM> at the bottom of the filter chamber <NUM>. Air introducing means <NUM> is provided for introducing air into the filter chamber <NUM> during filtration. The air introducing means <NUM> comprises an air supply conduit <NUM> and is configured to allow air to be drawn into the filter chamber <NUM> through a plurality of air inlets <NUM> as water W is drained from the filter chamber <NUM>.

The operation of the mechanical filter apparatus <NUM> to perform filtration and backwashing is unchanged from the embodiment described above. The mechanical filter apparatus <NUM> is illustrated performing filtration in <FIG>. During filtration, the tapered configuration of the filter chamber <NUM> helps to compact the filter elements <NUM> together as they are displaced downwardly by the down flow of water W through the filter chamber <NUM>. During backwashing, the water W is drained from the filter chamber <NUM> and the volume available for movement of the filter elements <NUM> increases as the level of the water W drops. The air introducing means <NUM> allows air to be drawn into the filter chamber <NUM> by the reduced pressure in the filter chamber <NUM> caused by the water W draining from the filter chamber <NUM>. The air enters the filter chamber <NUM> through the air inlets <NUM> and bubbles upwardly through the water W thereby promoting agitation of the filter elements <NUM>. At least in certain embodiments the tapered profile of the filter chamber <NUM> may facilitate filtration and backwashing.

A further embodiment of the mechanical filter apparatus <NUM> is shown schematically in <FIG>. Like reference numerals are used for like components. In this arrangement, the filter chamber <NUM> comprises a convex profile along said longitudinal axis. The sidewall <NUM> in the present embodiment comprises or consists of a spheroid. The spheroid could be truncated, top and/or bottom, to form a part-spheroid. The filter chamber <NUM> has a substantially circular cross-section in a plane perpendicular to said longitudinal axis. A plurality of filter elements <NUM> disposed in the filter chamber <NUM> performs mechanical filtration of the water W. The filter elements <NUM> form a filter pack <NUM> for performing mechanical filtration.

The mechanical filter apparatus <NUM> comprises a liquid supply conduit <NUM> for supplying unfiltered water to a liquid inlet <NUM> formed in the filter chamber <NUM>. The mechanical filter apparatus <NUM> also comprises a liquid return conduit <NUM> for returning filtered water W from a liquid outlet <NUM> formed in the filter chamber <NUM>. The liquid inlet <NUM> is disposed at the bottom of the filter chamber <NUM> and the liquid outlet <NUM> is disposed at the top of the filter chamber <NUM>. The water W flows upwardly through the filter chamber <NUM> from the liquid inlet <NUM> to the liquid outlet <NUM>. In the present embodiment, the filter elements <NUM> have substantially neutral buoyancy or positive buoyancy. The up flow of water W causes the filter elements <NUM> to form a filter pack (not shown) at the top of the filter chamber <NUM>. Air introducing means <NUM> is provided for introducing air into the filter chamber <NUM> during filtration. The air introducing means <NUM> comprises an air supply conduit <NUM> and is configured to allow air to be drawn into the filter chamber <NUM> through a plurality of air inlets <NUM> as water W is drained from the filter chamber <NUM>.

The operation of the mechanical filter apparatus <NUM> to perform filtration and backwashing is unchanged from the embodiment described above. During filtration, the tapered configuration of the filter chamber <NUM> helps to compact the filter elements <NUM> together as they are displaced upwardly towards the top of the filter chamber <NUM> by the up flow of water W. During backwashing, the water W is drained from the filter chamber <NUM> and the volume available for movement of the filter elements <NUM> increases (due to the increasing cross-section of the filter chamber) as the level of the water W drops to the vertical mid-point of the filter chamber <NUM>. Thereafter, the volume available for movement of the filter elements <NUM> decreases (due to the decreasing cross-section of the filter chamber) as the level of the water W drops below the vertical mid-point of the filter chamber <NUM>. The air introducing means <NUM> allows air to be drawn into the filter chamber <NUM> by the reduced pressure in the filter chamber <NUM> caused by the water W draining from the filter chamber <NUM>. The air enters the filter chamber <NUM> through the air inlets <NUM> and bubbles upwardly through the water W thereby promoting agitation of the filter elements <NUM>. At least in certain embodiments the tapered profile of the filter chamber <NUM> may facilitate filtration and backwashing.

It will be appreciated that the arrangement of the filter apparatus <NUM> shown in <FIG> may be reversed such that the filter elements <NUM> form a filter pack at the bottom of the filter chamber <NUM> during filtration. As described herein, this arrangement may be implemented by reversing the arrangement of the liquid inlet <NUM> and the liquid outlet <NUM> such that a down flow of water W is established through the filter chamber <NUM>.

The configuration of the filter chamber <NUM> may be further modified from the arrangements already described herein. The filter chamber <NUM> could, for example, have a convex profile along said longitudinal axis defined by a sidewall <NUM> comprising or consisting of a double-cone, as shown in <FIG>. Furthermore, to form said convex profile along said longitudinal axis, the filter chamber <NUM> may be defined by a sidewall <NUM> comprising or consisting of a part-spheroid, as shown in <FIG>. The filter chamber <NUM> may be circular, polygonal or elliptical in cross-section (i.e. perpendicular to the longitudinal axis X-X).

It will be appreciated that various changes and modifications may be made to the embodiments of the mechanical filter apparatus <NUM> described herein without departing from the scope of the present application.

The mechanical filter apparatus <NUM> has been described herein with reference to an arrangement in which the drain conduit <NUM> has a common connection to the filter chamber <NUM>. In particular, the drain conduit <NUM> is connected to either the liquid supply conduit <NUM> or the liquid return conduit <NUM>, depending on which of the liquid inlet <NUM> and the liquid outlet <NUM> is disposed at the bottom of the filter chamber <NUM>. In alternative embodiments, the drain conduit <NUM> can be separate from the liquid inlet <NUM> and the liquid outlet <NUM>. For example, a separate drain conduit <NUM> may be connected to a drain outlet (not shown) formed at or proximal to the bottom of the filter chamber <NUM>. In this arrangement, the liquid supply valve <NUM> may optionally remain open during backwashing. The drop in pressure in the filter chamber <NUM> when the drain valve <NUM> is opened is sufficient to draw air into the filter chamber <NUM> to agitate the filter elements <NUM>. Indeed, in certain embodiments, the pump <NUM> may continue to operate during backwashing such that the supply of unfiltered water W to the filter chamber <NUM> continues. The control strategy described herein may be modified such that the liquid supply valve <NUM> remains open and the pump <NUM> continues to operate during backwashing to supply unfiltered water W to the filter chamber <NUM>. It will be appreciated that the liquid supply valve <NUM> could be omitted in certain variants.

The filter chamber <NUM> has been described herein as having a substantially constant profile along said longitudinal axis. The configuration of the filter chamber may be modified according to modified arrangements of the present invention. By way of example, one or more baffles or restrictions may be provided in the filter chamber. It is envisaged that one or more annular member may be disposed inside the tubular member <NUM> forming the filter chamber <NUM>. The one or more annular member may each comprise first and second conical surfaces arranged to form a concave restriction in the sidewall of the filter chamber.

The drain valve <NUM>, the liquid supply valve <NUM> and the liquid return valve <NUM> are described herein as being controlled by the ECU <NUM>. An electromechanical actuator may be provided for actuating the drain valve <NUM>, the liquid supply valve <NUM> and the liquid return valve <NUM>. The electromechanical actuator(s) may comprise a solenoid or a servo actuator. Other types of actuated valve are also contemplated. In a modified embodiment, the liquid supply valve <NUM> and/or the liquid return valve <NUM> may comprise a one-way (check) valve.

The mechanical filter apparatus <NUM> has been described herein as incorporating a sealed filter chamber <NUM> capable of supporting an operating pressure greater than atmospheric pressure. It will be understood that the mechanical filter apparatus <NUM> may be modified such that the operating pressure in the filter chamber <NUM> is less than atmospheric pressure. In particular, the mechanical 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.

Claim 1:
A filter system (S) comprising a filter apparatus (<NUM>) and a pump (<NUM>) for pumping a liquid (W) to the filter apparatus (<NUM>); wherein the filter apparatus (<NUM>) comprises:
a filter chamber (<NUM>) comprising a plurality of mechanical filter elements (<NUM>) for forming a static filter pack (<NUM>) to perform mechanical filtration of the liquid (W), the mechanical filter elements (<NUM>) each having an open cell structure comprising one or more filter cells;
the filter apparatus (<NUM>) is configured to generate a flow of the liquid through the mechanical filter elements (<NUM>) during filtration;
wherein during filtration the filter apparatus (<NUM>) is configured to establish a flow rate per unit cross-sectional area of the static filter pack (<NUM>) greater than <NUM><NUM>/m<NUM>/h exclusive.