Patent ID: 12246293

DETAILED DESCRIPTION OF THE INVENTION

With reference to the accompanying drawings, embodiments of diffusers for aeration of a fluid will now be described.

With reference toFIGS.1to5, an embodiment of a diffuser in accordance with the present disclosure, generally designated10, comprises a flexible member20which may be an elastomeric membrane, and a diffuser base body30.

As illustrated inFIGS.1A and1B(referred to collectively asFIG.1), the diffuser base body30in this embodiment comprises a main surface32, which is, in normal use, upwardly facing. The main surface32is provided on an in-use upper wall34of the diffuser base body30. The main surface32is recessed in an in-use downwards direction. In this embodiment, at least part of the main surface32is curved so that at least some of the main surface is lower than it would be if the main surface were planar. In this embodiment at least part of the main surface the32is part cylindrical, although it should be appreciated that other geometries of curvature could be used. Similarly, in this embodiment, at least part of the in-use upper wall34is part cylindrical. The diffuser base body30may be pultruded or extruded using plastic, fibre reinforced or glass reinforced plastic or metal such as aluminium. It could also be roll formed from metal material such as stainless steel or even 3D printed. The break lines inFIG.1Aare intended to indicate that the base can be cut, or otherwise manufactured to substantially any manageable length.

The diffuser base body30further comprises first and second side walls36,38on which the upper wall34is supported in use. In this embodiment, the first and second side walls36,38are substantially parallel and are laterally spaced apart by the upper wall34.

Depending from a bottom region of each of the first and second side walls36,38is a respective inwardly directed flange wall40,42.

The diffuser base body30further comprises first and second attachment regions44,46for attachment of the flexible member20to the diffuser base body30. In this embodiment, the attachment regions44,46are provided substantially where the upper wall34meets the first and second side walls36,38but it will be appreciated that in other embodiments, they could be provided wholly on the upper wall34or wholly on the first and second side walls36,38.

Each of the first and second attachment regions44,46defines a corresponding groove45,47for receiving a sealing strip25,26of the flexible member20illustrated inFIG.2(which will be described further below).

The diffuser base body30may be regarded as being of generally rectangular cross section defining an interior channel48, which is open at the bottom of the diffuser base body30, as the laterally inward ends of the inwardly directed flange walls40,42are spaced apart. However, the main surface32, and in this embodiment the in-use upper wall34, is recessed towards the centre of the channel48. Further, the first and second attachment regions44,46depart from a rectangular shape. Of course, alternative embodiments may be differently shaped without departing from the scope of the present disclosure.

As illustrated inFIG.2, the flexible member20comprises a sheet of flexible material21dimensioned to fit upon the diffuser base body30. The flexible member20has a generally laterally central region22and first and second lateral side regions23,24. Provided at or adjacent the side regions23,24are respective first and second sealing strips25,26, which extend along the side regions23,24in the length direction of the flexible member20. In this embodiment, the sealing strips25,26are in the form of deformable projections which, in this embodiment, widen as they project further from the sheet of flexible material21to facilitate retention in the groove45,47and may be regarded as bulbous in form. In this embodiment, a wider part of each sealing strip25,26has an internal void or passageway27,28which extends along the sealing strip. The internal passageways may assist deformation of the sealing strips, and thus insertion into the grooves45,47, but are not necessary in all embodiments.

The flexible member20may be regarded as having an in-use internal face29A and an in-use external face29B, with the sealing strips25,26projecting from the internal face29A.

The flexible member20may be formed by extrusion, with the sealing strips25,26integrally formed therein. Other embodiments may provide sealing strips formed separately to membrane, for example, providing a sheet membrane and separate sealing strips which may be forced into grooves of the diffuser body in order to retain lateral edges of the sheet in the grooves, for example, in a manner corresponding to the way splines are used to retain edge regions of sheets of fly screen material frames provided for use in door or window openings.

FIG.3illustrates, in transverse cross section, the diffuser10assembled for use, and with the flexible member20overlaid on the main surface32of the diffuser base body30. The sealing strips25,26are retained in the grooves45,47.

It will be understood that wider parts of the sealing strips25,26are deformable such that they compress when forced through the relatively narrow openings of grooves45,47and then expand to press against the inner surface of the grooves, to thereby provide a sealed connection of the flexible member20to the diffuser base body30. Moreover, sealing strips5and grooves4are dimensioned such that the sealing strips are held within the grooves once the flexible member20has been fitted to the diffuser base body30. The retention and/or sealing of the sealing strips25,26in the grooves45,47may, if desired, be enhanced by inserting one or more substantially incompressible members (such as solid rod or wire), or by application of a fluid which subsequently cures to become substantially solid, into the internal voids or passageways27,28or by application of a of sealant material suitable to adhere to both the flexible member20to the diffuser base body30.

This connection of the flexible member20to the diffuser base body30provides an effective seal along the lateral sides of the diffuser10. It should be appreciated that the diffuser10may be many metres long, as will be described in more detail in due course. (It will be appreciated that there is a need to provide a seal between the flexible member20and the diffuser base body30at the ends, as well as along the lateral sides, and also to provide ingress of air into the diffuser, and these aspects will be described in due course.)

The configuration illustrated inFIG.3corresponds to a condition in which there is substantially no gas pressure applied to the diffuser10. Substantially the entire width of the flexible member20is in contact with the main surface32of the diffuser base body30. The flexible member20is relaxed and not stretched. The flexible member20is provided with small slits or other apertures to allow air to pass from the interior side29A to the exterior side29B, to allow bubble formation. In the relaxed and unstretched condition of the flexible member20, these apertures are substantially closed. Thus, in this condition, the flexible member20lies smoothly along the main surface32of the diffuser base body30without open slits or apertures, so that it effectively prevents ingress of waste water (or other liquid in which the diffuser10is immersed) to prevent ingress of liquid into the diffuser or into associated pipework via the diffuser. To achieve this, It is important to have the flexible member20accurately dimensioned for the diffuser: if the flexible member20is too loose the excess material will likely cause it to crease and split, and if the flexible member20is too taut, the slits will open without application of air to stretch it, likely allowing unintended and undesirable ingress of liquid. To help ensure an appropriate dimensional fit throughout the life of the flexible member20, it is important to provide a flexible member20which will provide minimal creep during its operational life.

FIG.4illustrates, in transverse cross section, the assembled diffuser10, and the configuration illustrated inFIG.4corresponds to a condition in which there is sufficient gas pressure applied to the diffuser10to cause the flexible member20to flex and to inflate, but not to substantially stretch. The inflation of the flexible member20creates a gas-filled interior compartment50between the flexible member20and the main surface32of the diffuser base body30, which effectively forms a pipe or conduit which can distribute air along the length of the diffuser10. This pipe or conduit is formed without stretching or stressing of the flexible member20or opening of the apertures or slits therein. The cross sectional size of the interior compartment50, and thus the capacity of the pipe or conduit which it forms, can then be increased by increasing the applied gas pressure, as will be described below. The action of inflating the flexible member20to a convex profile as shown inFIG.4promotes the removal of any debris which may settle on the membrane during non-operating time such as in an intermittent aeration application (e.g. in Sequential Batch Reactors (SBR) or Intermittently Decanted Extended Aeration (IDEA)).

FIG.5illustrates, in transverse cross section, the assembled diffuser10, with a configuration corresponding to a working condition, in which there is sufficient gas pressure applied to the diffuser10to cause the flexible member20to stretch, so that the perforations or slits open and air can pass therethrough and form bubbles in the liquid in which the diffuser10is immersed.

The increased applied gas pressure, compared to the condition ofFIG.4, causes stretching of the flexible member20, which increases the cross sectional size of the size of the interior compartment50, and thus the capacity of the pipe or conduit which it forms.

It will be appreciated that the pipe or conduit or conduit formed by the interior compartment50is relied upon for distribution of gas/air along the length of the diffuser10. No other pipe or conduit structure is provided by the diffuser10between its ends, and no other pipe relied upon for distributing gas between the ends of the diffuser.

It will further be appreciated that the recessed shape of the main surface32plays an important role.

The interior compartment50is provided by the inflated (and/or) stretched flexible member20, and the main surface32. At either lateral side of the compartment50, the compartment is bounded by a lateral side which may be regarded as the most inward point of contact between the flexible member20, and the main surface32. These lateral sides are designated S1and S2inFIG.5. By way of illustration of the recessed nature of the main surface32, a straight line between S1and S2is included inFIG.5, shown as a dashed line52. From comparison of the dashed line52and the main surface32, it can be seen that the recessed shape of the main surface32substantially increases the cross sectional size of the interior compartment, compared to use of a straight or planar surface extending between the lateral sides S1, S2of the interior compartment50.

Further, the initial formation of an interior compartment50which effectively forms a pipe or conduit, without stretching of the flexible member20, by applying a relatively low air pressure, and then incremental increase in gas pressure to stretch the flexible member20to increase the size of the pipe or conduit which it provides, help avoid deformation or creasing of the flexible member20which might damage it, and thereby assist in providing a flexible member20with a long working life. In the described embodiment, features of the diffuser10at or adjacent the ends of the diffuser, which will be described hereafter, also contribute to avoiding application of undue stresses to the flexible member20.

The flexible member inflates (without substantial stretching) at any pressure greater than the surrounding fluid pressure (but insufficient to substantially stretch the flexible member).

The flexible member stretches, and the diffuser diffuses air, at pressures ranging from approximately 2 kPa to approximately 15 kPa above the surrounding fluid pressure, depending on the air flux and condition of the diffuser, for example, as a result of fouling from precipitates and biological films.

The formation of the compartment between the unstretched flexible member and the base enables air to be distributed over considerable axial lengths of diffuser before the flexible member is required to stretch. This effectively provides an axially extending conduit, formed between the flexible member and the base, so that it is not necessary to provide a separately formed conduit (such as an enclosed conduit formed in or below the base) for distributing the gas along substantial lengths of diffuser.

By way of comparison with diffusers of the type disclosed in Australian Patent No. 745191 (to Aquatec Maxcon), in which stretching of the flexible member (membrane) is required to provide a compartment between the flexible member and the base so that the compartment can act as a conduit, attempts to distribute gas along lengths similar to those achievable by diffusers in accordance with the present disclosure resulted in the membrane becoming unstable and fluttering (oscillating rapidly and erratically) causing the air distribution to be poor and the membrane to fatigue rapidly.

In a particular embodiment of the diffuser base body30, the width of the diffuser base body30is about 15.5 cm. A radius of curvature of the recessed surface32(which in this embodiment is part-cylindrical) is about twice the width of the diffuser base body30. The wall thicknesses are mostly about 3-4 mm (although wall thicknesses are greater in some areas, such as adjacent the grooves46,47). Of course, alternative dimensions and shapes could be used, including much thinner material, as little as 1 mm in thickness.

FIGS.6to9Cillustrate a practical embodiment of a diffuser in accordance with the present disclosure. As the embodiment ofFIGS.6to9Cis consistent with the schematic cross sectional views ofFIGS.3to5, corresponding reference numerals are used. It will be understood that the schematic cross sectional views ofFIGS.3to5do not show components of the diffuser10other than the flexible member20and the diffuser base body30, but thatFIGS.6to9Cdo include additional components.

It should be appreciated that although illustrated as being fairly axially short for ease of illustration, the illustrated diffuser10may be very large in axial length compared to its lateral width. By way of example, in one successfully tested embodiment, the width of the diffuser10is approximately 15.5 cm, and the length approximately 12 metres, so that the length is approximately 75 times the width. Practical embodiments may be limited to about 6 metres in length for ease of transportation, although greater lengths, probably up to about 12 metres may be practicable under some circumstances.

FIG.6illustrates in schematic perspective view, the diffuser10in a condition in which there is no air flow. The flexible member20is in contact with the recessed main surface32along most of the length of the diffuser10, corresponding to the configuration illustrated inFIG.3. However, it should be noted that at the ends60,61of the diffuser10, the end regions of the flexible member20are retained and sealed by retaining clamps1400in a cross sectional shape substantially corresponding to the inflated but not stretched shape of the flexible member20illustrated inFIG.4, that is, with laterally central region22of the flexible member20extending outwardly (which in this embodiment corresponds to an upwards direction) beyond the side regions23,24. Further, the flexible member20transitions between the end (convex) and axially central (concave) shapes smoothly and fairly gradually. In an embodiment, this gradual transition is facilitated by shaped end pieces (1000,1200, but not shown inFIG.6) which will be described in due course. The gradual transition in shape of the supported flexible member is provided by a surface (which will be described in more detail in due course) onto which the flexible member20can collapse, in the absence of gas pressure, without causing wrinkles or other stress inducing features.

It will also be noted that the diffuser is provided with an air inlet1250and with a plurality of mounting plate arrangements1700to facilitate mounting to a bottom of a pool, a frame, or to some other object or structure as desired.

FIG.7illustrates in schematic perspective view, the diffuser10in a condition in which there is full working air flow. The flexible member20is inflated and stretched, so that the axially central region is substantially in the cross sectional configuration illustrated inFIG.5. However, discussed above in relation toFIG.6, the end regions of the flexible member20are retained in configuration substantially corresponding to the inflated but not stretched shape illustrated inFIG.4. Thus again, there is a transition between the end regions (held in the inflated but not stretched shape) and the central region along most of the length of the diffuser10, corresponding to the inflated and stretched configuration illustrated inFIG.5. This transition is fairly gentle, as it is a transition between the inflated and unstretched shape and the inflated and stretched shape. It should be appreciated that a transition region of similar axial length, but providing a transition between the uninflated shape (ofFIG.3) and a fully inflated and stretched shape would likely be substantially less gentle and inflict substantially greater stress on the transition region of the flexible member20.

FIG.8illustrates in schematic perspective view, the diffuser10, as shown in FIGS.6and7, but with the flexible member20omitted so that interior detail of the diffuser10can be seen. The internal features shown inFIG.8can also be seen inFIGS.9B and9Cwhich show the flexible member20partially cut away rather than omitted. Further,FIG.9Aillustrates that an air inlet is provided at one end61of the diffuser10, while the other end62is blanked off.

For most of the length of the diffuser10, the surface which in use faces the interior surface29A of the flexible member20comprises the main surface32, which has a recessed cross sectional shape as shown, for example, inFIG.1.

However, at the axial ends61,62of the diffuser10, the diffuser base surface34is inclined to provide a gentle transition between the recessed surface shape and an end surface shape which corresponds generally to the somewhat bulging shape of the inflated but not stretched flexible member20, as illustrated inFIG.4. As foreshadowed above, this allows a gentle transition between the axially central and end shapes of the flexible member20, assisting in reducing stress on, and premature damage to, the flexible member20.

The first end and second end transitions in the illustrated embodiment are provided by shaped end pieces1000,1200, which are also illustrated separately inFIGS.10and12, respectively.

Each of the shaped end pieces1000,1200comprises a blocking portion1010,1210and a tapered region1020,1220.

The blocking region1010,1210is shaped and dimensioned to substantially fill an axially short length of the recess provided by the recessed main surface32, and further to provide a first support surface part1012,1212extending beyond the recess, to support an end region of the flexible member20in its inflated but not stretched shape. Thus, the blocking region may have a transverse cross sectional shape which is substantially the same as the cross sectional shape of the shape of the internal compartment50as illustrated inFIG.4(as can be seen inFIG.12).

The tapered region1020,1220is contiguous with the blocking region1010,1210and provides a base engaging surface1022,1222which is shaped to conform closely to the recessed main surface32of the diffuser base body30, and a second support surface part1024,1224which in use extends from the first support surface part1012,1212to the recessed main surface32of the diffuser base body30. The tapered region1020,1220thus reduces in both height and lateral width as it extends away from the blocking region1010,1210.

The shaped end pieces1000,1200may be attached to the diffuser base body30in any desired manner. By way of non-limiting example, this could be achieved by use of a suitable glue or adhesive, sealant, double sided tape, solvent welding material or fasteners (screws or clips). It would also be possible to hold them in place using certain types of clamping member used to retain a flexible member (membrane) in sealed connection with the rest of the diffuser at the diffuser ends. If necessary, appropriate seals, such as O-rings or other seals, could be used to provide sealed integrity of the diffuser, including the interior compartment50, as required. As foreshadowed elsewhere, the tapered shape provided by the shaped end pieces1000,1200could, if desired, be provided by appropriately shaped end regions of the diffuser base body30.

The shaped end piece1000used at the first end61of the diffuser10provides an air inlet arrangement1050, integrally formed therewith. The air inlet arrangement1050comprises a passage1030which extends through the shaped end piece1000and which has a gas outlet1032provided as an opening in the second support surface part1024and a gas inlet1034provided by a pipe connection1036in fluid communication with the passage1030and projects externally of the diffuser10. The pipe connection1036is adapted for connection to an air supply pipe or hose, and may comprise any suitable type of connection, for example, a male, or spigot-type, connection, or a female, or socket-type, connection. Further, any desired type of connection-securing arrangement, such as a screw threaded or other type of hose or pipe coupling may be used.

The air inlet1050may be provided with a check valve1060(sometimes called a non-return valve) as a precaution against any liquid which might have undesirably entered the interior compartment50flowing into the gas supply pipe (not shown) that feeds gas to the diffuser. Many types of check valve are known per se, and any suitable check valve arrangement could be used (for example, a ball check valve, a diaphragm check valve, a swing check valve or the like). In the illustrated embodiment, the check valve1060is a lift check valve provided at the opening1032and comprises a disc or lift1062, which can be lifted off a seat formed by the opening1032, and which is retained in the opening by a stem1064attached to the a disc or lift1062being retained in a guide1066which is mounted in the opening. A seal1068may be provided between the disc1032and the opening1032to enhance sealing when the check valve1060is closed. The manner in which a lift check valve works will be understood by the skilled addressee, and will not be described in further detail.

In this embodiment, in order to accommodate the pipe part of the air inlet, and allow the shaped end piece1000which includes the pipe part to be fitted on to the diffuser body30, in-use upper wall34of the diffuser body30is provided with a cut-out1070at the (or each) end of the diffuser10at which a shaped end piece with a pipe is to be fitted.FIG.10Cshows an end region of the diffuser body30in which a cut-out1070is provided. The cut-out1070is formed by removing some of the in-use upper wall34between two remaining side regions1072,1074of the diffuser body30. In this embodiment, the side regions1072,1074each comprise part of the structure that forms the attachment regions44,46and an adjoining side-part of the in-use upper wall34. That is, some of the laterally central region of the in-use upper wall34is missing, to provide the cut-out.

The shaped end piece1000may also incorporate a fail closed valve which, in the event of a membrane failure, will shut off air flow to the failed diffuser thereby maintaining air pressure in the rest of the feed system to be maintained, and allowing the remaining diffusers in the aeration system to operate normally. It has been known for failure of a diffuser membrane (e.g. flexible member20) to result in the very large amount of air escaping through the inoperative diffuser compromising the aeration process performed by other, connected, diffusers to an extent where the grid with the failed diffuser must be isolated from the aeration process.

A fail closed valve suitable for such use may comprise a valve which is effectively a gas fuse valve, which is a type of valve known per se, used to prevent flow of gas therethrough in response to an undesirably great flow of gas. A fail closed valve suitable for use such use may comprise a valve member which remains in an open (effectively inoperative) position when the air flow is below a threshold level, the threshold level being above normal operating air flow levels, and which moves into a closed (or air shut-off) position in response to the air flow exceeding the threshold level, and then remains in the closed position, despite the air flow level dropping due to operation of the valve. In an embodiment the valve may comprise a member having a tapered surface, which is arranged to be moved into engagement with a complementary tapered surface in response to air flow above the threshold level, with the engaged position corresponding to a closed position of the valve member. The taper may be a ‘self-holding’ class of taper, such as for example a Morse taper, so that after activation (closure) the valve remains in the closed condition despite the air flow level dropping (to zero and/or to below the threshold level) due to operation of the valve. In one alternative the valve may comprise a gate-like valve member which is normally open and is arranged to be moved into a closed position in response to air flow above the threshold level and a latch arrangement to retain the gate-like valve member in the closed position after activation despite the air flow level dropping (to zero and/or to below the threshold level) due to operation of the valve. While the fail closed valve may be incorporated into the shaped end piece1000, such a valve may be provided elsewhere in the air supply system of a diffuser.

The shaped end piece1200is for blanking off the second end62of the diffuser10, and therefore does not include an air inlet or internal passageway. However, if it is desired to connect two or more diffusers10in series, so that one diffuser supplies gas to the next in series, then a diffuser which supplies gas can have a shaped end piece at its second end which provides a gas outlet (not shown). In this case, the shaped end piece at the second end of the diffuser, which provides the outlet, could be similar or identical to the illustrated shaped end piece1000, but without the check valve (and, of course, acting as a gas outlet rather than a gas inlet).

FIGS.11A and11Bshow a shaped end piece1100which is similar to the shaped end piece1000, but a variation thereof which is shaped slightly differently. That is, a blocking region1110of end piece1100extends further in the axial direction than does the blocking region1010of end piece1000, and correspondingly a first support surface part1112extends further in the axial (length) direction of the diffuser than does first support surface part1012(but is, like first support surface part1012, provided to support an end region of the flexible member20in its inflated but not stretched shape. Further, tapered region1120, is axially shorter than the tapered region1020of shaped end piece1000, and the boundary between the first and second support surface parts1124,1112is curved, rather than being substantially straight like the boundary between the first and second support surface parts1024,1012, so that the first and second support surface parts1124,1112overlap in the axial direction.

FIGS.14A and14Billustrate an embodiment of a retaining clamp1400, which is an embodiment of an end sealing part.

The retaining clamp1400, in this embodiment, comprises an end clamping portion1410which is adapted to press or clamp an end region of the flexible member20against an end of the diffuser. Thus, a seal can be provided between the flexible member20and an end of the diffuser body and/or tapered end piece.

The retaining clamp1400, in this embodiment, comprises an axially extending upper clamping portion1420(which extends somewhat and, in this embodiment, a short distance, in the axial direction of the diffuser). The axially extending upper clamping portion1420in use overlies a region of the flexible member20close to the end thereof and is adapted to press or clamp this part of the flexible member20against a surface of the diffuser body30and/or shaped end piece1000,1200which extends in an axial or length direction of the diffuser. In this embodiment, the axially extending upper clamping portion1420in use presses the corresponding part of the flexible member20against the first support surface part1012,1212of a shaped end piece1000,1200.

In this embodiment, the retaining clamp1400, further comprises an axially extending lower clamping portion1430(which extends somewhat and, in this embodiment, a short distance, in the axial direction of the diffuser). The axially extending lower clamping portion1430in use underlies a region of the flexible member20at to the end thereof and is adapted to press or clamp this part of the flexible member20upwardly against a surface of the diffuser body30and/or shaped end piece1000,1200which extends in an axial or length direction of the diffuser. In this embodiment, the axially extending lower clamping portion1430is contoured to follow the curves of a bottom surface of the end part of the diffuser base, which in this embodiment, at the inlet end of the diffuser, is provided by the end regions of the side regions1072,1074of the diffuser body30on either side of the cut-out1070, and a bottom surface of an end part of the shaped end piece1000which extends between the side regions1072,1074. The axially extending lower clamping portion1430thus comprises first and second lateral side parts1433,1436contoured to fit the lower surfaces of the side regions1072,1074and a more laterally central part1439, contoured to fit the lower surface of the shaped end piece1000.

The retaining clamp1400, further comprises an attachment arrangement for attaching it relative to the rest of the diffuser10. The fixing arrangement may comprises one or more apertures, each for receipt of fastening member therethrough. In this embodiment, two such apertures1412,1414are provided, each for receipt of a fastener, e.g. a threaded fastener such as a screw1413,1415therethrough.

It will be appreciated that an end sealing part which comprises only one of an end clamping portion or an axially extending clamping portion may (in certain embodiments) be sufficient to provide a suitable end seal. In the illustrated embodiment, the retaining clamp1400comprises both the end clamping portion1410and the upper and lower axially extending clamping portions1420,1430, which is considered to assist in providing a robust seal and to assist assembly of the diffuser, including retention of the end portion of the membrane during application of the fasteners and positioning of the retaining clamp1400. The axially extending clamping portion1420, especially where the surface which bears against the external face29B of the flexible member corresponds substantially to the shape of the flexible member when the flexible member20is inflated by not stretched, can also assist in avoiding application of undue stresses to the flexible member.

FIG.15Aillustrates a length1500of flexible member20which has been manufactured or tailored (for example, from a cross sectionally uniform extrusion) for securing to a diffuser base body30of a particular length, using shaped end pieces1000,1200and retaining clamps1400.

The length1500of flexible member20provides an end region1510in a form suitable for being passed around or over an end of the diffuser base body30and an axially outer end of a shaped end piece1000,1200. In this embodiment, the end region1510is free from sealing strips25,26which extend along most of the length1500of flexible member20. If the length1500of flexible member20is prepared from a cross sectionally uniform extrusion, the end parts of the sealing strips25,26may be simply cut or trimmed off. The end region1510is also provided with apertures1512,1514for passage of fastening members (e.g. screws1413,1415) therethrough. The apertures1512,1514may be formed in appropriate positions prior to attachment of the length1500of flexible member20to the diffuser base body30, or if appropriate taking into consideration the characteristics of the flexible member20may be made after attachment to the diffuser base body30and positioning of a retaining clamp1400, for example, by insert of screws or a separate step such as use of a heated awl or the like. A further, opposed end region1520may correspond to the end region1510.

FIG.15Billustrates schematically the shape of a lateral half of the length1500of flexible member20when it is secured to a diffuser base body30using shaped end pieces1000,1200and retaining clamps1400, but does not show those other components of the diffuser10.

With reference toFIG.16, the sealed attachment of the length1500of flexible member20to the diffuser base body30can be performed as follows. It will be appreciated thatFIG.16shows only one end, but that the arrangement at the other end may correspond, and will be apparent to the skilled addressee from the following description. In this embodiment, the sealed attachment may be performed by inserting (and securing) the sealing strips (25,26, but not shown inFIG.16) of the flexible member20in the corresponding grooves45,47of the diffuser base body30, and then wrapping end regions1510(which is short in axial length and which does not have sealing strips25,26) around the end of the diffuser body, including around the terminal (blocking region) end of the shaped end piece1000, and then retaining the end region1510of the flexible member20in sealed connection with the other components by applying and securing retaining clamp1400over the axial end of the diffuser base body30and shaped end piece1000. The wrapping of the end regions1510around the end of the diffuser body will include some stretching of the end regions1510. The assembly is secured by screws1414,1415which are passed through the apertures1412,1414in the retaining clamp1400, through the apertures1512,1514in the membrane, and into the grooves45,47of the diffuser base body30. Clamping forces applied by the retaining clamp1400may be increased, or adjusted, as needed by adjustment (tightening or loosening) of the screws, to provide a desired seal.

The diffuser10may include mounting plates1700for mounting the diffuser to a floor of a tank, or to a frame (not shown).

FIGS.17to19illustrate an embodiment of a two part mounting plate1700for mounting the diffuser to a floor of a tank, or to a frame.

In this embodiment, the two part mounting plate1700comprises two substantially identical mounting plate parts1700A,1700B.

With reference to one mounting plate part1700A, each of the parts1700A,1700B comprises a groove1710for accommodating at least some of a side region of the diffuser10, such that the mounting plate part can slide along the engaged side region in the axial direction of the diffuser10.

In the illustrated embodiment, the groove is for accommodating part of one of the inwardly directed flange walls40,42.

Each mounting plate part1700A,1700B has a laterally inwardly directed part1702which in use projects from the groove1710, part of the distance towards the side of the diffuser10which is not engaged by the groove1710, so that in use it extends substantially laterally inwardly from the engaged side of the diffuser, but across a distance less than the entire width of the diffuser10.

Each mounting plate part1700A,1700B further comprises a laterally outwardly directed part1704which in use projects from the groove1710, laterally outwardly relative to the diffuser. The laterally outwardly directed part1704, provides a fixing formation1706, in this embodiment, in the form of a reinforced aperture, for facilitation fixing of the mounting plate1700to a mounting structure such as the floor of a tank or a frame for mounting diffusers thereon.

The mounting plate part1700A further comprises an engaging formation for engaging the other mounting plate part1700B. The engaging formation, in this embodiment, comprises a projection1720for engagement within a complimentary recess of the other mounting plate part1700B, and a recess1730for receiving a complimentary projection of the other mounting plate part1700B.

In this embodiment, the groove1710, the projection1720and the recess1730extend in substantially parallel directions.

In use, the mounting plate part1700A, with a first-side inwardly directed flange wall40engaged within its groove1710, can slide along first-side inwardly directed flange wall40in the axial direction of the diffuser, and the other mounting plate part1700B, with a second-side inwardly directed flange wall42engaged within its groove1710, can slide along the second-side inwardly directed flange wall42, also in the axial direction of the diffuser.

Thus, in use, the two the mounting plate parts1700A,1700B can be slid towards (and away from) each other.

Because the laterally inwardly directed part1702does not extend the entire width of the diffuser, it can be placed substantially in the channel48of the diffuser10at substantially any desired axial position along the length of the diffuser10. Thus, each mounting plate part1700A,1700B can be positioned in engagement with the diffuser at substantially any desired axial position along the length of the diffuser10.

In use, the mounting plate parts1700A,1700B are positioned in engagement with opposite sides of the diffuser10at axial positions of the diffuser10close to a position where it is desired to locate a mounting plate, with the projection1720of each mounting plate part1700A,1700B extending towards the other mounting plate part.

When the mounting plate parts1700A,1700B are slid into engagement, the projection1720of each mounting plate part is received in the complimentary recess1730of the other mounting plate part, with a fit sufficiently tight to prevent relative lateral movement of the two mounting plate parts1700A,1700B.

The two mounting plate parts1700A,1700B thus effectively provide a single mounting plate which can be used to mount the diffuser by use of the fixing formation1706.

The two part mounting plate1700provides a mounting plate which can be readily attached to the diffuser base body30at the required axial location rather than having to be inserted at an end and slid along from the end to the desired position. This becomes increasingly beneficial as the axial length of the diffuser increases.

FIG.19illustrates how the mounting plate parts1700A,1700B in a particular embodiment can be engaged with the (e.g. diffuser body30). Each groove includes a widened region1712for allowing the mounting plate parts1700A to be fully engaged with an inwardly directed flange wall40,42by partial insertion into the groove1710and then rotation of the mounting plate parts1700A,1700B to provide full insertion of the flange wall40,42into the groove1710.

It should also be noted that the laterally outwardly directed part1704is, when the mounting plate1700is assembled and horizontal, vertically offset from, and higher than the laterally inwardly directed part1702. Thus, when fasteners such as screws or bolts (not shown) are used in the apertures1705to force the outwardly directed parts1704downwardly, substantial opposed torques (or rotational forces) will be applied to the connections between the grooves1710and the flange walls40,42and between the projections1720and the recesses1730. These forces effectively lock the mounting plate parts1700A,1700B together, and prevent sliding relative to the diffuser body, once the fasters are tightened.

It will be appreciated that a variation could provide two projections on one of the component parts of a two part mounting plate, and two complementary receiving recesses on the other of the component parts. Further variation could provide different numbers of projections and complementary receiving recesses, including the possibility of a single projection on one of the component parts of a two part mounting plate, and a single complementary receiving recess on the other of the component parts.

An arrangement in which both parts, e.g.1700A,1700B, of the two part mounting plate are identical can assist in reducing manufacturing cost, for example, by requiring only a single mould, rather than two different moulds, for manufacture by injection moulding. Further, the parts, e.g.1700A,1700B, are each smaller than a similar single-piece mounting plate would be, allowing use of a smaller injection mould and moulding, and hence providing a reduction in cost. Further, having both parts, e.g.1700A,1700B, of the two part mounting plate identical means that any two parts can be used together to provide the assembled mounting plate, avoiding the possibility of wasted time resulting from a worker inadvertently selecting two parts that cannot be assembled together, or in ensuring that parts are provided in usable sets or pairs.

FIGS.20A to20Cillustrate a variation2000in which gas is fed into a diffuser at an axially central region thereof, rather than from an end. In this embodiment, the diffuser2000is provided with a gas inlet which is centrally located. In such an embodiment, both ends may have shaped end pieces for blanking off the ends, so that the both of the shaped end pieces may be similar or identical to the shaped end piece1200ofFIG.12. Alternatively, the shaped end pieces may allow the passage of air for connection of further diffusers at either or both ends. The central gas inlet may include a check valve, and an example is illustrated inFIGS.13A and13B.

As foreshadowed above, the diffuser disclosed herein is designed to form its own “pipe” by creating an elongate interior compartment along which air may be distributed along the length of the diffuser, so that no convention pipe or hose, and no conduit defined entirely or almost entirely by the diffuser base body is required.

The ability of the diffuser to distribute gas along the length of the diffuser via the internal compartment is enhanced by incorporating a recessed or concave curve, rather than the flat or typical upwards or convex curve into the part of the body of the diffuser that forms part of the boundary of the interior compartment. The recessed part can, but does not necessarily, extend across the entire surface of the body that forms part of the boundary of the interior compartment, but at least in preferred embodiments, should be sufficient to increase the cross sectional size of the interior compartment or “pipe’ compared to the body providing a planar surface to bound the interior compartment (all other things being equal).

This conduit or “pipe” effect means that diffusers can be provided with significantly longer axial length than many (possibly any) previously commercially available fine bubble strip diffusers. Diffusers in accordance with the present disclosure have been demonstrated to successfully deliver air to the end of a diffuser at least 12 m long. Diffusers in accordance with the present disclosure avoid the occurrence of excessively high local velocities in the distributed gas, which can otherwise cause drag on the membrane thus cause the membrane to flutter and act in an unstable manner.

Further, use of longer diffusers allows fewer hose or pipe connections, and fewer components to be used, which can provide efficiencies in cost and efficiency of assembly and/or installation.

Of course, shorter lengths are also possible with the disclosed diffusers if desired or necessary to meet the dimensions of the reactor to be aerated. These can be of any shape including rectangular, square and circular or combinations of these, e.g. oxidation ditches.

The cross sectional shape of the diffuser base body disclosed herein is simple, making easier to form, for example by extrusion or pultrusion than diffuser bodies that are more complex in cross sectional shape (for example, because the body itself defines an interior conduit).

Further, some known diffusers using bodies formed of plastic and which include a pipe-like or hollow diffuser body, are in use sufficiently buoyant that resultant uplift forces require substantial ballast or more or larger restraints (compared to at least some embodiments described herein) to hold the diffuser in place while in service.

Another beneficial feature of at least some embodiments is that the underside of the diffuser is unrestricted other than at mounting supports (mounting plates). It does not include any additional lateral supports, webs, or internal conduit parts that would increase the likelihood of it holding o trapping biological material which could putrefy. It has been known for the profile of some commercially available diffusers to undesirable trap mixed liquor within conduit parts thereof.

Another beneficial feature of at least some embodiments is that the diffuser is that the action of inflating the flexible member20to a convex profile (as shown inFIG.4), promotes the removal of any debris which may settle on the membrane during non-operating time. It will be noted that the diffuser10, as a whole, has a profile which slopes downwardly (as shown) from the top of the inflated membrane, and is free from upwardly extending external protrusions which would be likely to trap debris and prevent the removal of debris from the membrane when the flexible member (membrane) is inflated. (The action of air bubbles being emitted from the diffuser aids the transport of debris material from the upper surface of the membrane and diffuser, but in some known diffusers this has proven insufficient to avoid debris being trapped.)

FIGS.21and22illustrate alternative embodiments2100,2200, in which the recessed surface which bounds the interior compartment is much more recessed, and has a much greater curvature than that illustrated inFIGS.1to16and20. This can provide an interior compartment2150,2250(and thus a resulting pipe or conduit, effectively formed by the interior compartment) which has a greater cross sectional size for a given width of the diffuser. For example, a radius of curvature, in the transverse direction may be of the order of half the width of the diffuser. While embodiments of this type may be useful under some circumstances, it is often undesirable to have a diffuser which is too narrow, as this may adversely affect bubble distribution, and a suitably wide diffuser with an internal compartment with cross sectional shape as shown inFIG.21or22may be more buoyant than is desirable. Selecting an appropriate cross sectional shape may therefore include balancing capacity to distribute gas along the length of the diffuser, diffuser width, buoyancy and other factors.

The cross sectional shape of the embodiment ofFIGS.1to5is considered suitable for a wide range of typical wastewater aeration applications, providing sufficient cross sectional area in the interior compartment for the distribution of air for diffusers up to 12 m long, the greatest length likely to be readily handled and transported, while avoiding unnecessary buoyancy and associated uplift.

Of course, the above features or functionalities described in relation to the embodiments are provided by way of example only. Modifications and improvements may be incorporated without departing from the scope of the invention.

Some examples of envisaged variations and alternative embodiments and variations which may be incorporated without departing from the scope of the present disclosure are described hereafter.

Different attachment/sealing of the membrane to the diffuser base at the ends may be used. A number of different type of devices and arrangements for sealing the membrane and base at the ends of strip diffusers are known per se, and in variations or alternative embodiments any suitable known type could be used. For example, any one or more of screwed clamps, spring clips, sealant, glue etc. could be used without departing from the scope of the present disclosure.

Different attachment/sealing of the membrane to the base at the lateral sides. Engagement of a bulb (whether integrally formed with the membrane or provided as a separate, spline-like, sealing strip) has been described in detail, but it should be appreciated that there are other known arrangements for sealing the membrane and base along the lateral edges of strip diffusers, and in variations or alternative embodiments any suitable known type could be used. For example, in one alternative form of edge seal, known per se in the field of diffusers, the membrane may be clamped to the base along or adjacent the lateral sides thereof. In such an arrangement lateral side regions of the membrane may be folded over, or otherwise conformed in shape to, lateral side regions of the base either prior to or at least partly as a result of the action of, application of one or more clamp members.

An issue that sometimes arises in use of diffusers for aerating wastewater is that when warm humid air enters the piping system which feeds the diffusers, water may condense on the walls of the pipes (including the downcomer) which convey pressurised air from blowers or compressors to the diffusers. The condensate may pool in low lying areas of the pipes and may build up over time, causing problems, especially if the height of the accumulated water reaches the height of the diffuser membranes. These problems can include adverse effects on air distribution through the piping system, including reduced air flow at the diffusers, and fouling of the back (interior) sides of the diffuser membranes. This issue can be exacerbated in intermittent aeration applications. Water could be purged manually using a suitable manual purge valve system. This would rely on plant operators performing such purging on a regular basis.

With reference toFIGS.23to31, a valve arrangement which can allow automatic purging of water from a piping system which feeds air diffusers will be described. It will be appreciated that the disclosed valve arrangement may have other uses, particularly in situations where water is to be purged from submerged air (or other gas) supply pipes.

With reference toFIGS.23to31, a valve arrangement generally designated by the reference numeral2300, comprises a float valve arrangement and a duckbill valve arrangement, which act together to allow purging of water from a feed pipe of an air diffuser while resisting entry of water, in which the diffuser and feed pipe are submerged, into the feed pipe.

As shown in the exploded views ofFIGS.23and24, the valve arrangement2300comprises a float member2310, which in the illustrated embodiment is generally cylindrical in external shape and which has a tapered lower end region2312. The tapered lower end region2312is substantially conical in shape in the illustrated embodiment.

The float member2310is, in use, provided within a tubular float guide2320, which is provided with slots or apertures2322for allowing passage of water that is to be purged therethrough. In the illustrated embodiment the slots2322comprise first and second higher axially extending slots2322A, which in this embodiment are diametrically opposed, and a lower axially extending slot2322B. In the illustrated embodiment the slots2322A,2322B each have an angular extent of about 45 degrees (in the transverse circumferential direction of the float guide2320) and the lower axially extending slot2322B has an angular separation from each higher axially extending slot2322A of about 45 degrees. The lower axially extending slot2322B allows water accumulated on the floor of the air feed pipe to flow to the purge outlet, as will be described in due course.

The valve arrangement2300further comprises a duckbill valve2330. The duckbill valve2330comprises a first end region2332, which provides an inlet end of the duckbill valve2330and may also, in use, be regarded as defining a valve arrangement outlet2333through which water can be purged. The first end region2332also provides an outwardly extending flange2332A. The duckbill valve2330further comprises a second end region2334, which provides an outlet end of the duckbill valve2330. The second, outlet, end region2334of the duckbill valve2330comprises opposed elastomeric parts which are adapted to be forced apart by excess pressure from an upstream (duckbill valve inlet end) direction to allow fluid to flow through the duckbill valve, but which are biased together to a valve closed configuration to resist or prevent flow of fluid through the duckbill valve in the reverse direction. In the illustrated valve arrangement2300the duckbill valve is constructed in one piece from an EPDM rubber or similar flexible elastomer material and has an operational diameter of between 4 mm to 6 mm, although embodiments include duckbill valves with operational diameters up to about 20 mm or more. It will be appreciated that the structure and operation of duckbill valves is known per se, and will not be described in detail herein.

The valve arrangement2300further comprises a duckbill retainer2340for retaining the duckbill valve2330relative to a valve housing part2350(and, in the illustrated embodiment, relative to a pipe or the like from which water is to be purged). The duckbill retainer2340provides a first end region2342, an intermediate region2343and a second end region2344.

The intermediate region2343has an exterior cylindrical wall provided with a male helical thread, which facilitates connection to the valve housing part2350.

The first end region2342, which is above the intermediate region2343in use, is of slightly smaller external diameter than the intermediate region2343and provides a flange accommodating recess2347(shown inFIG.24) for accommodating the outwardly extending flange2332A of the duckbill valve2330. The depth of the flange accommodating recess2347is slightly smaller than the thickness of the flange2332A, so that when the flange2322A is located in the flange accommodating recess2347(with a lower surface of the flange2332A engaging the bottom of the recess) the uppermost part of the flange2332A can project upwardly a small distance out of the recess, and an upper surface of the flange2332A is slightly higher than, and proud of, an upper surface of the duckbill retainer2340. By way of example, in an embodiment the thickness of the flange is 2 mm and the depth of the flange accommodating recess2347is 1.75 mm. This allows the upper surface of the flange to be forced against a surface provided by the valve housing part2350(as will be described hereafter) to effect a seal2332A, while helping to prevent undesired deformation of the flange2332A by having most of the thickness of the flange2332A located in and supported by the flange accommodating recess2347.

The second end region2344, which is lower than the intermediate region2343in use, provides a hexagonal exterior configuration to facilitate fastening and unfastening of the duckbill retainer2340to the valve housing part2350using a rotational fastening tool of the type used to operate a hexagonal head of a bolt, or a hexagonal nut.

The duckbill retainer2340is provided with a passageway2346which extends substantially axially therethrough. In use the passageway2346accommodates part of the duckbill valve2330and allows water to flow therethrough. The axial passageway2346is of sufficient diameter to give clearance to the duckbill valve2330so that its operation is not compromised. The flange accommodating recess2347may be regarded as a widened upper termination of the passageway2346.

It will be appreciated that in the illustrated embodiment the check valve arrangement2300is incorporated into a shaped end piece2400, which is suitable for feeding air into a first end of a diffuser and which has many similarities in form and function to shaped end piece1000described above, the description of which should be considered incorporated into the description of shaped end piece2400. Further, it will be appreciated that the following description in relation to the shaped end piece2400, other than that relating to the purge valve arrangement, may be of direct relevance to the shaped end piece1000and other shaped end pieces described above.

The shaped end piece2400provides an air inlet arrangement2450, integrally formed therewith. The air inlet arrangement2450comprises a passage2430which extends through the shaped end piece2400and which has a gas outlet provided as an opening2432in a support surface part2424and a gas inlet2434provided by a pipe connection2436in fluid communication with the passage2430. The pipe connection2436is adapted for connection to an air supply pipe or hose, and may comprise any suitable type of connection, for example, a male, or spigot-type, connection, or a female, or socket-type, connection. Further, any desired type of connection-securing arrangement, such as a screw threaded or other type of hose or pipe coupling may be used.

The air inlet2450is provided with a check valve2460(sometimes called a non-return valve) comprising a disc or lift2462, which can be lifted off a seat formed by the opening2432, and which is retained in the opening2432by a stem2464attached to the a disc or lift2462which is retained in a stem guide2466provided in the opening2432. A stem retainer2467, which is of greater diameter than the stem2464, is in use attached to the bottom of the stem2464so that the stem is retained in a part of the stem guide2466which is of large enough diameter to accommodate the stem2464, but impassable by the stem retainer2467, thus limiting upwards travel of the lift2462.

A seal2468is provided between the lift2462and the opening2432to enhance sealing when the check valve2460is closed.

As illustrated inFIG.24, and alsoFIGS.25and26, the shaped end piece2400provides a substantially horizontally extending groove2470into which an edge of an upper wall of a diffuser base may be received in order to facilitate connection of the shaped end piece2400to the diffuser base. In the illustrated example, the groove2470may be shaped to receive an edge of an upper wall34of diffuser body30which defines cut-out1070, as illustrated inFIG.10Cdescribed above.

The valve arrangement further comprises a valve housing part2350, which in this embodiment is provided as part of the air inlet arrangement2450(or air feed pipe) which feeds air to the diffuser. The valve housing part2350provides an upper circular recess2352, for seating the bottom of the tubular float guide2320, and a lower circular recess2354for accommodating much of the duckbill retainer2340. The lower circular recess2354provides a female helical thread on its internal wall, so that the duckbill retainer2340can be screwed into the lower circular recess2354. An upper part2356of the lower circular recess2354is of reduced diameter and in use receives at least part of the first end region2342of the duckbill retainer2340, and an in use upper part of the duckbill valve, including the flange2332A. A small shoulder2358is provided between the upper circular recess2352and the upper part2356of the lower circular recess2354, against which the upper part of the duckbill valve2330, and in particular the part corresponding to the upper surface of the outwardly extending flange2332A of the duckbill valve2330, is pressed, in use, by the duckbill retainer2340. The threaded engagement of the duckbill retainer2340and lower circular recess2354provide firm, sealed engagement of the flange2332A against the shoulder2358by tightening of the threaded connection when the duckbill retainer2340is screwed into the lower circular recess2354. Undesired deformation of the flange2332A (and consequent deformation of the valve arrangement outlet2333, which might compromise sealing) is substantially prevented by most of the thickness of the flange2332A being located in and supported by the flange accommodating recess2347. The axial length of the first end region2342of the duckbill retainer2340and the axial length of the upper part2356of the lower circular recess2354are dimensioned to provide a good seal between the flange2332A and the shoulder2358, while avoiding the possibility of the first end region2342bearing unduly hard against (and possibly damaging) the shoulder2358when the intermediate region2343of the duckbill retainer2340is fully tightened into the (main, wider part of the) lower circular recess2354.

The upper circular recess2352and lower circular recess2354are in fluid communication to provide an outlet passage through which water may be purged. However, it should be appreciated that the minimum diameter of this outlet passage, at the small shoulder2358, is larger than the diameter of the valve arrangement outlet2333provided (in use) by the duckbill valve2330, so the opening of the duckbill valve effectively provides the valve arrangement outlet2333. As will be described hereafter, this provides, in use, a part which the tapered lower end region2312of the float member2310can seal against, and which being made of elastomer, rubber or the like, assists in providing an effective seal.

The outlet is preferably provided substantially at the lowest point of the diffuser air feed passage, and effectively provides an outlet in the floor, or lowest part, of the air feed passage.

FIG.25is a schematic side view of the embodiment ofFIG.23, assembled, and in a passive, non-air flow configuration, showing some internal detail in broken lines, andFIG.26is a schematic end view thereof, also showing some internal detail in broken lines.

FIGS.27and28are, respectively, schematic cross sectional views corresponding to the sections B-B and A-A inFIGS.26and25respectively, illustrating the assembly and configuration of the various parts when the air feed system and diffuser are a in a passive, non-air flow state.

In the passive, non-air flow configuration illustrated inFIGS.25to28, the diffuser check valve2460is closed and the lift2462and stem2464are in their lowest positions. In this configuration the bottom of the stem retainer2467rests gently upon the top of the float member2310enhancing sealing of the tapered lower end region2312against the valve arrangement outlet2333provided by the duckbill valve2330, and further maintaining the seal even in the presence of water which may need to be purged from the air feed passage.

Even in the passive, non-air flow configuration, when the head pressure of water outside the air feed passage is greater than the air pressure within the air feed passage, the duckbill valve2330is effective in preventing water from entering the air feed passage, as the resilient ‘lips’ of the duckbill valve form a watertight seal which is not broken by the external water pressure.

FIG.29is a schematic side view of the embodiment ofFIG.23, assembled, and in an active, air flow, configuration, showing some internal detail in broken lines.

FIG.30is a schematic longitudinal cross sectional view corresponding to the view ofFIG.27, but showing the active, air flow, configuration, andFIG.31is a schematic transverse cross sectional view corresponding to the view ofFIG.28, but showing the active, air flow, configuration.

As illustrated inFIGS.29to31, when air is supplied to the diffuser, the diffuser check valve2460is opened and the lift2462and stem2464are in their raised positions. In this configuration the bottom of the stem retainer2467is raised to be clear of the top of the float member2310, allowing the float member to rise, due to its buoyancy, if there is pooled water which needs to be purged. A raised position of the float member2310is illustrated inFIGS.29to31. In the raised position the tapered lower end region2312of the float member2310, is no longer sealed against (nor in contact with) the valve arrangement outlet2333provided by the duckbill valve2330. Thus the valve arrangement outlet2333is effectively opened, providing a fluid passageway between the pooled water on the floor of the air inlet passage and the duckbill valve2330. In the air supply state the air feed passageway is pressurised (normally to a pressure sufficient to expel air through the diffuser membrane into the surrounding water which is being treated) to a pressure greater than the head pressure of the water outside the diffuser and the air supply passage, and the air pressure inside the air supply passage forces the water to be purged through the duckbill valve2430in a purging action.

As the water to be purged is expelled from the air feed passage the water level in the air feed passage reduces, and the float member2310, which is floating on the pooled water, descends accordingly. When all water the water to be purged has been expelled from the air feed passage the float member2310reseats the tapered lower end region2312thereof against the valve arrangement outlet2333provided by the duckbill valve2330, effectively sealing the outlet and preventing undesired expulsion of air through the purge valve arrangement2300. The air pressure in the air feed passageway may assist in forcing the float member into sealed engagement with the valve arrangement outlet2333.

The described embodiment can therefore provide a purge valve which automatically purges accumulated water from the air feed pipe when air pressure is applied, which controls undesired expulsion of pressurised air therethrough, and which resists ingress of water, even when the air feed passage is not pressurised.

The float member2310is an example of a purge control element which is movable between a first control position in which it is not floating, for closing the water outlet when there is little or no accumulated water to be purged, and a second control position in which it floats due to the presence of water to be purged, thereby leaving a water outlet (in this embodiment valve arrangement outlet2333) open, so that water can be purged therethrough.

The duckbill valve2330is an example of a flow check valve through which water is, in use, purged, and is a one-way valve which allows flow of water therethrough in the purging direction and in use substantially prevents flow of water therethrough in the reverse direction.

FIGS.32to36illustrate an alternative embodiment of valve arrangement, generally designated by reference numeral3200, in which the float member is in the form of a ball float3210, rather than a generally cylindrical member (designated2310inFIGS.23to31) which has a tapered lower end region2312.FIGS.32and33show exploded views andFIGS.34to36illustrate internal detail and configuration in the circumstances that no air is being supplied to the diffuser, and no water requiring purging has accumulated. Thus the ball float3210is located on, and blocking the outlet. Initial consideration suggests that the use of a ball provides an inferior seal against the outlet, compared to the generally cylindrical member (designated2310inFIGS.23to35) with its tapered lower end region2312. It will also be appreciated that, as illustrated, in contrast to the embodiment ofFIGS.23to31, the position of the lift2462and stem2462of the diffuser check valve2460do not provide a downward force upon the float member in the closed configuration of the diffuser check valve2460to retain the floating member against the outlet (although, the dimensions of the stem and related components could be adjusted to provide such a force, if desired).

It will be appreciated that further variations are possible.

In the described embodiments of the purge valve arrangement the purge valve is provided in substantially the same location as the diffuser air check valve (e.g.1060,2460) and the tubular guide for the stem of the diffuser air check valve is extended to the floor of the air feed passage and used as the tubular float guide2320. However, it should be appreciated that the purge valve arrangement need not be provided at or adjacent the diffuser air check valve, and could be provided in any desired position in the air feed passage.

Further, the floating member is not limited to the shapes described and could be any appropriate desired shape. The floating member may be hollow to provide a desired degree of buoyancy water, and/or may be or constructed from a material which has a suitable specific gravity, currently considered to be provided by a density less than 80% of that of water.

Further, if desired, a resilient member (e.g. a helical spring) or other biasing mechanism could be could be provided in the float guide (e.g. float guide2320) to lightly bias the floating member downwardly and thereby improve sealing of the floating member against the outlet, while not preventing floating of the float member in the presence of water to be purged (at least, not in an active, air flow, state of the valve arrangement).

Further, although an example of a suitable assembly has been provided, alternatives are possible. For example, in the described embodiments the duckbill retainer is described as connecting to the valve housing part by means of screw threaded connection, but alternatives such as gluing or press fitting are possible.