FIELD OF THE INVENTION

The present invention relates to flap-type check valves and duck-beak type check valves applied to positive displacement pumps.

BACKGROUND TO THE INVENTION

The "duck beak" type of flexible tube check valve is used to stop the reflux of tidal waters into sewer and storm water outlets that discharge into open waters. It was also used as the outlet check valve on World War Il gas masks.

Current commercial "duck beak" check valves rely on a flexible fabric reinforcement embedded in a soft elastomer tube or flap to support the valve closure against pressure when closed. Higher pressure capacity, and a need to revert to a closed configuration in the relaxed state, requires increasing layers of reinforcing fabric and tube wall thickness with consequent loss of flexibility to the point where the required wall thickness becomes impractical.

Diaphragm positive displacement pumps handling slurries typically have ball valves, or flap valves, at their inlet and outlets, and are limited in their capacity to pump large size solids.

OBJECTIVES OF THE INVENTION

To provide a means of increasing the pressure capacity of the "duck beak" (and flap type) check valve with less sacrifice of flexibility, or fatigue endurance, of the valve components, and to adapt these as the inlet, outlet, and venting check valves on positive displacement pumps pumping slurries containing large size granules.

PRIOR ART

In prior "International" Patent No. WO 2006/108219 novel adaptations of the prior art duck-beak valves were disclosed in which the flexible tube inlet of the duck beak surrounds a stiff thick-walled inlet-positioned tube (hereinafter termed a "spigot") extended in the direction of flow, which is cut diagonally to form an isometric V shape whose apex is co-planar with the axis of the valve. When viewed from a direction normal to the plane of each diagonal cut, each cut surface of the inlet tube appears as a half of an elliptical annulus. These two cut surfaces support the flexible parts of the check valve against external pressure: additional stiff reinforcing members support the flexible parts of the closed duck beak against valve outlet pressure when the valve is closed.

SUMMARY OF THE INVENTION

The present invention provides adaptations of check valves of the prior art as an inlet valve and an outlet valve and as vent valves for a positive displacement pump.

Accordingly, first aspects of the invention comprise a positive displacement pump comprising a central pumping part sealingly enclosed within a pump chamber wherein the central pumping part is driven reciprocatingly by a motor means within the pump chamber to increase or decrease a volume enclosed within the pump chamber, and wherein the pump chamber comprises an inlet port and a outlet port and a vent port; wherein the inlet port is positioned above the outlet port, and wherein the vent port is positioned above the inlet port, and the vent port comprises a vent port inlet, a vent port outlet and wherein entry to the vent port inlet is located adjacent the top of the pump chamber; wherein an inlet check valve having a first outlet communicating conduit-wisely with the pump chamber, and a first inlet, and an outlet check valve having a second inlet communicating conduit-wisely with the pump chamber at a location below the first outlet, and the outlet check valve having a second outlet, and whereby when the central part is moved by a motor means to increase the volume enclosed within the pump chamber and thereby draw fluid into the pump chamber, the inlet check valve opens and the outlet check valve closes, and when the central part is moved by the motor means to decrease the volume enclosed within the pump chamber and thereby expel fluid from the pump chamber, the inlet check valve closes and the outlet check valve opens, and wherein also the vent port outlet communicates conduit-wisely with a venting means comprising a flushing means whereby the venting means returns a controlled quantity of fluid to the pump chamber when the volume enclosed within the pump chamber increases, and wherein the hyphenated adverb conduit-wisely applies where flow of fluid between communicating parts is sealingly and securely enclosed without movement of the fluid being impeded. Accordingly, second aspects of the invention comprise the positive displacement pump of the first aspect wherein the inlet check valve and the outlet check valve both have extended sealing surface parts, whereby as each inlet check valve or outlet check valve closes, large granules entering the diaphragm pump become sealingly enshrouded by the extended sealing surface parts to close the check valve. Accordingly, third aspects of the invention comprise the positive displacement pump of the second aspect wherein the inlet check valve and the outlet check valve are a valve comprising a valve body with an inner wall sealing surface, a valve inlet and a valve outlet, a stiff tubular support adjacent the valve inlet comprising a tubular inlet portion and a tubular outlet portion, a flexible sheet providing the extended sealing surface parts when the valve is closed; wherein the flexible sheet is attached to the stiff tubular support adjacent the valve inlet, and wherein the tubular outlet portion is shaped to provide a sealing surface of an approximately elliptical annular shape that supports the flexible sheet when the valve is closed; wherein the stiff tubular support and the valve body are shaped so that the sealing surface of an approximately elliptical annular shape and inner wall sealing surface form an approximately continuous sealing surface that supports the flexible tube when the valve is closed, and wherein a reinforcement means supports the flexible sheet against superior pressure at the valve outlet where the stiff tubular support does not provide support, and the reinforcement means is provided by inner stiffening members and outer stiffening members that sandwich the flexible sheet between them, and wherein, when the valve is closed the extended sealing surface parts are provided by a first area of contact between the flexible sheet and the inner wall sealing surface, plus a second area of contact between the flexible sheet and the stiff tubular support and reinforcing means; wherein the first area of contact is at least two-thirds of the second area of contact.

Accordingly, fourth aspects of the invention comprise the positive displacement pump of the second aspect wherein the inlet check valve and the outlet check valve are each a valve comprising a valve body, a valve inlet and a valve outlet, a stiff tubular spigot adjacent the valve inlet comprising a spigot inlet portion and a spigot outlet portion, a flexible tube providing the extended sealing surface parts when the valve is closed; wherein the flexible tube has a flexible tube inlet and a flexible tube outlet; wherein the flexible tube comprises a tube inlet portion and a tube outlet portion; wherein the tube inlet portion is sealingly attached to the stiff tubular spigot adjacent the valve inlet and the tube outlet portion extends beyond the spigot outlet portion, and wherein the spigot outlet portion is shaped to provide three or more flat surfaces that support the flexible tube when the valve is closed; wherein the tube outlet portion is biased to fold as it closes with six or more inner surface parts of the tube outlet portion meeting to form three or more lobes of approximately equal size and equally spaced apart, but wherein the flexible tube opens towards forming an approximately tubular shape, and wherein a reinforcement means supports the flexible tube against a superior pressure at the valve outlet where the three or more flat surfaces do not provide support, and the reinforcement means is provided by three or more inner stiffening members each linked to outer stiffening members that sandwich the flexible tube between them; wherein each inner stiffening member pivots on the spigot outlet portion, and wherein each outer stiffening member is of a folded sheet form comprising a central bar part with a flat inclined wing part at each side; wherein each flat inclined wing part presses onto an outer surface of one of the lobes when the valve is closed; wherein each flat inclined wing part and the flat inclined wing part of an adjacent outer member sandwich one of the lobes between them when the valve is closed, and whereby an adjacent pair of outer stiffening members support each other when the valve is closed, and wherein also the six or more inner surface parts comprise surfaces immediately adjacent the spigot outlet portion and surfaces beyond the spigot outlet portion; wherein the surfaces beyond the spigot outlet portion are at least as extensive as the surfaces immediately adjacent the spigot outlet portion.

Accordingly, fifth aspects of the invention comprise the positive displacement pump of the second aspect wherein the inlet check valve and the outlet check valve are each a valve comprising a valve body, a valve inlet and a valve outlet, a stiff tubular spigot adjacent the valve inlet comprising a spigot inlet portion and a spigot outlet portion, a flexible tube providing the extended sealing surface parts when the valve is closed; wherein the flexible tube has a flexible tube inlet and a flexible tube outlet; wherein the flexible tube comprises a tube inlet portion and a tube outlet portion; wherein the tube inlet portion is sealingly attached to the stiff tubular spigot adjacent the valve inlet and the tube outlet portion extends beyond the spigot outlet portion, and wherein the spigot outlet portion is shaped to provide a first sealing surface of an approximately elliptical annular shape that supports the flexible tube when the valve is closed; wherein a reinforcement means supports the flexible tube against superior pressure at the valve outlet where the first sealing surface does not provide support, and the reinforcement means is provided by an inner stiffening member linked to an outer stiffening member with the flexible tube sandwiched between them to provide a second sealing surface; wherein the inner member pivots on the spigot outlet portion, and inner surfaces of the tube outlet portion meet to form a third sealing surface as the valve closes, and wherein the third sealing surface is as least extensive as the first sealing surface and the second sealing surface combined.

Accordingly, sixth aspects of the invention comprise a check valve comprising a valve inlet and a valve outlet, and a spigot of a stiff tubular form, and a flexible tube, and wherein the flexible tube comprises a first section adjacent the valve inlet, a second section adjacent the valve outlet biased by its construction to be closed in its relaxed state, and a third section between the first section and the second section that is longer than either the first section or the second section, and the third section is biased by its construction to be open in its relaxed state, and wherein the spigot has an inlet end adjacent the valve inlet, and an outlet end, and the first section is sealingly and securely attached around the spigot adjacent the inlet end whereby, when the internal pressure within the flexible tube sufficiently exceeds the external pressure the first section opens, but the second section opens only after the third section is almost fully open, and when the external pressure begins exceeding the internal pressure the second section closes first, and the third section progressively closes with fluid enclosed within the third section being progressively expelled by said external pressure through the first section and the valve inlet to provide a flushing quantity of fluid until the third section fully closes.

Accordingly, seventh aspects of the invention comprise the positive displacement pump of the first aspect and the check valve of the sixth aspect wherein the vent port outlet communicates conduit-wisely with a modified check valve having a third inlet and a third outlet, and comprising a pierced valve part pierced by an aperture that engages a valve seat when pressure at the third inlet exceeds the pressure at the third outlet and fluid issues from the vent port outlet to pass through the aperture and the modified check valve, and wherein the pierced valve part lifts away from the valve seat when pressure at the third outlet exceeds the pressure at the third inlet and fluid enters the vent port outlet; whereby when fluid issues from the vent port outlet the aperture restricts the rate of flow of the fluid, and when fluid issues from the third inlet to enter the vent port outlet the pierced valve part lifts away from the valve seat and the aperture does not restrict the rate of flow of the fluid through the modified check valve; and wherein the third outlet communicates conduit-wisely with the valve inlet of the check valve, whereby fluid is expelled at a restricted rate from the check valve when the the volume enclosed within the pump chamber is decreasing, and a flushing quantity of fluid is returned to the positive displacement pump through the modified check valve and the vent port when the volume enclosed within the pump chamber is increasing. Accordingly, eighth aspects of the invention comprise the positive displacement pump of the first aspect and wherein an inside wall is defined in the pump chamber and the inlet check valve comprises a flexible sheet attached hingedly above the first outlet and extends to cover a first area of the inside wall surrounding the first outlet when the valve is closed; wherein the flexible sheet moves to press against the inner wall to close the inlet check valve, and the flexible sheet moves away from the inner wall to open the inlet check valve, and wherein a reinforcement means supports the flexible sheet against superior pressure at the valve outlet where the inside wall does not provide support, and the reinforcement means is provided by an inner stiff plate and an outer stiff plate that sandwich the flexible sheet securely and sealingly between them by a bolting means; wherein the inner stiff plate can move freely within the first outlet but the outer stiff plate extends to cover an annular area surrounding the first outlet, whereby the outer stiff plate and the inner stiff plate together support the flexible tube against a superior pressure within the pump chamber when the valve is closed, and where the flexible sheet extends peripherally beyond the outer stiff plate to sealingly and flexibly enshroud granules when the valve is closed, and wherein the outer stiff plate covers a second area and the first area is more than one and one half times the second area.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a duck-beak check valve in cross section in the closed position with embedded stiffening bars bridging the two sides of the openings of the spigot. A check valve comprising a valve body, a valve inlet and a valve outlet, a stiff tubular spigot adjacent the valve inlet comprising a spigot inlet portion and a spigot outlet portion ,a flexible tube providing the extended sealing surface parts when the check valve is closed; wherein the flexible tube has a flexible tube inlet and a flexible tube outlet; wherein the flexible tube comprises a tube inlet portion and a tube outlet portion; wherein the tube inlet portion is sealingly attached to the spigot inlet portion adjacent the valve inlet and the tube outlet portion extends beyond the spigot outlet portion ; wherein the spigot outlet portion is shaped to provide a first sealing surface of an approximately elliptical annulus shape that supports the flexible tube when the check valve is closed; wherein a reinforcement means supports the flexible tube against superior pressure at the valve outlet where the first sealing surface does not provide support, and the reinforcement means is provided by an inner stiffening member linked to an outer stiffening member with the flexible tube sandwiched between them to provide a second sealing surface; wherein the inner stiffening member pivots on the spigot outlet portion, and inner surfaces of the tube outlet portion meet to form a third sealing surface as the check valve closes, and wherein the third sealing surface is as least extensive as the first sealing surface and the second sealing surface combined.

Figure 2 is the Figure 1 view with the valve in the open position.

Figure 3 is a side view of a duck-beak check valve shown with one half of the valve in cross section.

Figure 4 is a split end view in cross section of the valve of Figure 3 in the directions of the staggered arrows XX-XX.

Figure 5 is a side view in half cross section of an elongated flexible tube type check valve arranged to entrap fluid while opening and to expel that entrapped fluid through its inlet while closing.

Figure 6 is a side view of a flap-type check valve in cross section with the flexible flap extended beyond the stiff flap.

Figure 7 shows an end view in cross section on the arrows Y-Y of Figure 6.

Figure 8 shows a side view of a flexible tube type check valve in half cross section where the closed outlet parts form three lobes.

Figure 9 shows an end view in cross-section on the arrows Z - Z of Figure 8.

Figure 10 shows the end view of Figure 9 with the valve in the open position.

Figure 1 1 is a schematic side view in cross section of a diaphragm pump fitted with extended sealing surface check valves as the inlet and outlet check valves with a flexible tube vent valve discharging to the atmosphere.

Figure 12 is a schematic side view in cross section of a diaphragm pump fitted with extended sealing surface check valves as the inlet and outlet check valves with a Figure

5 type valve serving as the vent valve, with the vent valve discharging downstream of the outlet check valve. Figure 13 is a schematic side view in cross section of a diaphragm pump fitted with extended sealing surface check valves like those of Figure 12 with an extended flap valve serving as the inlet check valve, wherein the vent valves arrangement is similar.

Figure 14 is a schematic side view in cross section of a diaphragm pump fitted with extended sealing surface check valves like those of Figure 12 with a duck beak valve serving as the inlet check valve, and wherein the vent valve arrangement is similar to that of Figure 12.

Figure 15 shows details of a screen.

Figure 16 shows details of a flow restricting swing check valve.

Figure 17 shows a scrap view of the pierced valve viewed on the arrow AB of Figure 16. DETAILED DESCRIPTION OF PREFERRED ASPECTS

Preferred aspects of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which:

Figure 1 shows a side view in cross section of a check valve 10 bolted sealingly between pipes (shown in ghost outline) at the inlet 13 (with flange 15) and the outlet 14 (with flange 16). The valve is housed in the tubular enclosing chamber 12, and the valve is shown in the closed position. The flexible parts of the valve 81 shown in cross section can be either a duck beak tubular valve, or a duck beak valve with extended flaps open at each side. Figure 2 shows the check valve of Figure 1 with the valve 10 in the open position.

The vent port 83 is omitted from Figure 2.

In Figures 1 and 2 the tubular inlet spigot 72A is conically shaped on its outside at its inlet end and is cut to form a V with flat surfaces at its outlet end 72B. The uncut inlet conical shaped parts sealingly hold the inlet parts of the flexible duck beak tube 81 by compressing them against opposing conical shaped faces of the inlet flange 15.

The cut produces a half-elliptical annular shape with flat surfaces at each side of the outlet end of the inlet spigot tube 72, which can be seen when viewed from the direction of the arrow T. These cut surfaces provide two sealing surfaces 72B for the closed valve. The extended flexible parts of the duck-beak tube (or the extended parts of two flap valves) meet further downstream to provide the extended sealing surface.

The flexible parts 81 are supported by embedded stiff rods 82, where they bridge the two half-elliptical openings at 72B and serve resist a superior pressure at the outlet 14 when the valve is closed. The valve 10 is shown with its axis vertical and the inlet above the outlet, which favours the passage of solids through the valve, but entraps air entering the valve in the valve body 12. The vent port 83 allows a passage through which accumulated air can escape, provided a suitable means of venting the air is attached to this vent port. The downstream end 81 A of the tubular duck-beak valve 81 is thickened and biased by its construction to help hold the outlet part of the duck-beak valve closed when the valve inlet and outlet pressures are approximately equal.

Figures 1 and 2 also exemplify an alternative check valve wherein the extended sealing surface parts 81 are two opposing flexible flat sheets, anchored by being sealingly compressed between inclined surfaces of the central spigot 72A and the flange 15 on each side. In this alternative the extended sealing surfaces are the surfaces between the flat spigot surfaces 72B and the two flexible sheet parts 81 adjacent the spigot, and the flat surface between the closed flexible sheet parts 81 downstream of the spigot.

Figures 3 and 4 show a duck beak valve of the prior art 20 in which like numerals indicate features in common with Figures 1 and 2. They are examples from WO 2006/108219 (Figures 5 and 6). The flexible tube 1 1 is typically formed from synthetic rubber and reinforced with a strong embedded woven flexible fabric.

Figure 3 shows a side view in half cross section, and Figure 4 shows an end view in staggered cross section on the arrows XX — XX of Figure 3. In Figures 3 and 4 the flexible tube 1 1 is a straight tube with parallel walls of larger bore than that of the inlet spigot 101. The flexible tube 1 1 is typically formed from synthetic rubber and reinforced with a strong, but flexible, embedded woven fabric. The flexible tube 1 1 is sealingly clamped at its inlet end around the spigot 101 by clamping strap 109. The flexible tube 1 1 is narrowed over a squeezed outlet portion by pairs of stiff clamping bars 105 that permanently clamp each side of the flexible tube by the fasteners 106. They do not clamp the centre of the tube. This clamping of the sides biases the flexible tube flat when it is relaxed with its inner walls pressed together over the clamped length as shown in Figure 4, until the valve inlet pressure exceeds the valve outlet pressure sufficiently to open the valve. This arrangement also minimises deformations of the tube as it flexes, and may thus extend the service life of the tube. Clamping means 105 and fasteners 106 may be omitted where the flexible tube is biased by is construction to be closed in its relaxed state.

The flexible tube is a "lay flat" tube that may be rolled up like a fire hose, but expands to a circular shape/cross-section when filled with liquid. In the example it comprises nitrile rubber reinforced with fine Dacron fibres, although other materials may be used for the flexible tube. The spigot 101 is cut as shown to provide a V with inclined flat surfaces 101 A that support the flexible tube against externally applied pressure when the valve is closed as described above for Figure 1 . Additional support is provided by the stiff members 102, which are attached to the inner wall of the flexible tube by the rivets 104 and outer stiff plate 103. Stiff members 102 pivot about a groove at the inlet end of each flat surface 101 A. Entry of debris between the stiff member 102 and the spigot 101 as the valve opens is prevented by the expansion of sponge rubber insert 108. Flange 15, bolted cover plate 15A and the securing screws 1 13 allow the flexible tube to be sealingly encased within valve body 12, and allow for easy dismantling for flexible tube replacements. Figure 5 is a side view of an enclosed duck-beak valve 30 arranged to entrap fluid while opening and to progressively discharge that entrapped fluid through its inlet while the valve is closing. The valve is shown with one half of the valve in cross section, with an inlet 13E and an outlet 14E. The valve is shown in its relaxed state and comprises a flexible tube 1 10 sealingly clamped by hose clamp 109a around a hollow spigot 101 b at its inlet end and sealing lips 110a (that form a closed and flattened "duck beak" shape) at its outlet end, with a transition 1 10b from the duck beak shape to the longer tubular- shaped section between the duck beak and the spigot 101 b. The spigot 101 b is cut as shown to provide a V with inclined flat surfaces 101 c that support the flexible tube against externally applied pressure when the valve is closed as described above for Figures 3 and 4. The flexible tube is further supported against external pressure by the stiff members 102a and 103a, which sandwich part of the flexible tube 1 10 between them and are securely linked by the screws 104a, which are prevented from unscrewing by locking tab washers 105a. The flexible tube is shown at a time when external pressure is equal to the internal pressure and the duck beak 1 10a has just closed. As the external pressure increases the flexible tube upstream progressively flattens to lengthen the flattened part as indicated by the ghost lines 1 10D and 1 10C until it reaches the spigot inclined surfaces 101c. Further closing and flattening of the flexible tube is prevented by the stiff members 102a and 103a shown in their closed position by the ghost outlines 102c and 103c. The outer stiff plates have ribs 1 13b to provide additional stiffening against external pressure. As the valve 30 closes the fluid contained in the flexible tube (between the initial closing of the lips 1 10a, and the progressive collapse of the flexible tube 1 10, and the inwards movement of stiff members 102a and 103a to their closed positions 102c and 103c) is progressively displaced through the inlet 13E. Where the valve 30 is used as the vent valve of a diaphragm pump, and the fluid passes through a barrier screen upstream off the valve 30, and this displaced fluid serves to clean the barrier screen by "back-flushing" i.e. by reversing the fluid flow through it.

When the internal pressure within the flexible tube exceeds the external pressure the inner and outer stiff plates progressively open, the flexible tube progressively inflates, and the lips 1 10a open last. This provides the valve 30 with a fresh inventory of back- flush fluid to be discharged during the next progressive valve closing. Where the valve 30 is enclosed (as shown) the spigot is screwed into a boss 1 12, and sealed by an O-ring seal 1 12A. A stiff-walled conduit or hose 1 11 is sealingly attached to the boss 1 12 by the hose clamp 1 13, and encloses the flexible tube 1 10. The outlet end of the stiff walled hose 11 1 is sealingly connected to a further boss or inlet nozzle as required.

Where the valve 30 discharges to low-pressure surroundings, e.g. the atmosphere, the conduit 11 1 , the boss 1 12, and the hose clamp 113 can be omitted, and the stiff members 102a, 103a, and screws 104a, may be omitted.

Figure 6 shows a side view in cross section of an inclined axis flap-type check valve 50 in the closed position, with the inlet 13 above the outlet 14. The valve seat is provided by the slope-cut hollow spigot 21 with inclined flat surfaces 21 a, which provides a flat elliptically annular area for the valve seat. The flexible flap 23 extends beyond the outlet end, and beyond each side of the flat surfaces 21 A to provide extended sealing surfaces. Screws and nuts 27 sandwich the flexible flap 23 between the inner stiff member 22, and outer stiff member 26.

Figure 7 shows an end view on the arrows Y-Y of Figure 6 in cross section. Figures 6 and 7 are an example of an extended surface flap valve, and show a stiff inner flap 22 and a stiff outer flap 26, which correspond to the stiffening members 102 and 103 of Figures 3 and 4. Inner flap 22 has a cylindrical pivoting part 22A at its inlet end, which pivots in the groove 21 b. At its outlet end 22B the stiff inner flap is shaped to bear upon the inner wall of the spigot 21. The inner flap 22 supports the flexible flap 23 against higher pressures (at the valve outlet 14) than the flexible flap can carry by itself. When the valve is closed the flexible flap 23 seals against the stiff flat surface 101 A, but there is a gap 22C between the surface 101 A and the inner flap 22, where the flexible flap 23 is unsupported. Figure 7 shows the flexible flap 23 depressed by pressure into this gap 22C. This gap accommodates solids that may otherwise become ensnared in the gap. The gap is kept short, but its presence limits the outlet pressure at which the valve can operate. To accommodate higher pressures, an additional flexible flap (not shown in Figures 6 and 7) is placed between upper surface of the stiff inner flap 22, surface 101 A, and the inner surface of the flexible flap 23. This additional flexible flap contains short embedded rods that laterally bridge the gap 22C (similar to, but smaller and shorter than those of Figure 1 ). The advantage of these embedded rods is that they can enshroud solids that become trapped above the said gap. Figure 8 shows a side view in half cross section of an extended sealing surface check valve 60 comprising a flexible tube that flattens in its closed state (as shown) into three equally spaced and equally sized lobes. It is a further example of the duck beak valve disclosed in WO 2006/108219.

Figure 9 shows an end view in cross section on the arrows Z — Z of the valve shown in Figure 8 with the valve closed.

Figure 10 shows the end view in cross section of the valve shown in Figure 9 with the valve fully open.

In Figures 8, 9 and 10 numerals that are common to Figures 3 and 4 obtain a similar description: the flexible tube 1 1 is sealingly clamped at its inlet and outlet ends around the spigot 101 by clamping strap 109. The spigot 101 is cut as shown to provide three flat surfaces 101 A that partly support the flexible tube against externally applied pressure when the valve is closed. Additional support is provided by three inner stiff members 102, which are each attached to the inside wall of the flexible tube by rivets, screws, or bolts 104, and to the three outer stiff members 103. Stiff members 102 have cylindrical protrusions that pivot within grooves 102A at the inlet end of each flat surface 101 A. Although only two rivets or bolts 104 are shown for each stiff member 102 and stiff plate 103, a larger number may be needed to accommodate a higher external pressure.

As shown in Figures 9 and 10 each inner stiff member 102 and each outer stiff member 103 is curved to fit the contour of the expanded flexible tube, and each outer stiff member also has an inclined flat wing part 103a, and 103b, at each side that are angled at 120 degrees of arc from each other. These flat wing parts 103a and 103b limit the inwards travel of the inner and outer stiff members (and the flexible tube) when the valve closes and sandwiches a flattened lobe of the flexible tube 1 1 between them, as shown in Figure 9. Note that the dimensions of items 103a and 103b can be increased to accommodate high external pressures. Flange 15, bolted cover plate 15A and the securing nuts 1 13 allow the flexible tube to be sealingly encased within valve body 12. The screwed plug 1 15 allows access for venting of the valve chamber 17. Whereas a valve with three lobes is shown in this example, the arrangement can be readily extended to provide valves having more than three lobes. Figure 1 1 is a schematic showing a diaphragm pump 70 fitted with valves of

Figure 1 , or 3, or 6, or 8 serving as its inlet check valve 31 and its first outlet check valve 31 A. The diaphragm 52, is sealingly enclosed around its periphery between the flanges 51 B and 51 C. The diaphragm 52 is reciprocatingly driven by the shaft 53 to increase or decrease the volume enclosed in the pump chamber 55 (between the diaphragm 52 and the pump outer shell 51 A). Item 54 is the shaft driving motor. The diaphragm pump 70 is shown during its induction stroke with the pump chamber 55 volume increasing, the inlet check valve 31 open, and both the outlet valve 31 A and the vent valve 3OB closed. In Figure 1 1 numerals that are common to Figure 5 obtain a like description. A vent port 83 in the upper part of the valve body enclosing the inlet check valve 31 provides a means of venting entrapped gases from chamber 55 and thereby priming the pump. The vent valve 3OB comprises only the flexible tube 1 10 and the entry spigot 101 b of the valve 30 shown in Figure 5 where, when fluid enters through the spigot 101 b, the flexible tube 110 swells and the valve 110a at its end opens to discharge fluid through the vent valve 3OB. When fluid is being withdrawn through the spigot 101 b, the valve 1 10a closes, and the flexible tube 1 10 progressively collapses to discharge enclosed fluid through the spigot 101 b.

During a pump delivery stroke the diaphragm moves away from the shaft driving motor 54; the volume of the pump chamber 55 progressively diminishes, valve 31 A opens, increasing the pressure within the pump chamber and in the valve chamber space surrounding valve 31. Valve 31 closes and fluid is expelled and delivered through outlet 14, and through the flow-restricting check valve 32, and through the un-enclosed vent valve 3OB.

During a pump induction stroke the diaphragm moves towards the shaft driving motor 54; the volume of the pump chamber 55 progressively increases, reducing the pressure within the pump chamber and in the valve chamber space surrounding valve 31. Inlet valve 31 opens, valve 31 A closes, and fluid enters through inlet 13, and vent valve 3OB closes. The flow-restricting check valve 32 opens to allow fluid entrapped within the flexible tube of un-enclosed vent valve 3OB to enter the valve chamber space surrounding valve 31. By this means, air entering the pump chamber is progressively expelled through the vent valve 3OB, providing a means of priming the pump during initial reciprocations of the diaphragm, and also a means of continuously purging air from the pump. The return of fluid from the vent valve 3OB during each pump induction stroke serves to back-flush the flow-restricting check valve 32, and the screen 91. The screen 91 provides a barrier to granules that will not pass easily through flow-restricting check valve 32. In this example the vent valve 3OB is shown discharging upwards, but, by making appropriate changes, an alternative example wherein the vent valve 3OB is discharging downwards can be provided. An example of a screen is shown in Figure 15.

Figure 12 is a schematic showing a diaphragm pump 80 like that of Figure 11 , equipped with an alternative means of venting fluids from the top of the inlet valve and pump chambers, and discharging those vented fluids into a port 83A downstream of the outlet valve 31 A. In this figure like numerals indicate features in common with Figures 5 and 11 . A sealing cap 32A can be removed when servicing the pump to attach an external flushing hose to flush the interior of the inlet valve 31 chamber, screen 91 , and the pump chamber 55.

In this example the alternative means is the enclosed vent check valve 30 of Figure 5 wherein the conduit or hose 1 11 (of Figure 5) is sealingly anchored at its top around the vent valve 30 (to enclose the vent valve 30), and by a tubular ell conduit 68 to the inlet port 83A attached to the body of outlet check valve 31 A, whereby fluids vented through the vent valve 30 during delivery movements of the pump diaphragm 52 descend into the valve body enclosing outlet valve 31 A, and thereafter discharge through the outlet 14. The operation of the vent valve 30, flow-restricting check valve 32, and screen 91 , follows that provided above for vent valve 3OA, flow-restricting check valve 32, and screen 91 of Figure 1 1. Figure 13 is a schematic showing a diaphragm pump 90 like that of Figure 12, fitted with an alternative inlet port 13A and inlet check valve that is a flap valve comprising a flexible elliptical flap 41 that closes onto an area surrounding inlet port opening 13A, and the area of the inner wall 51 A of the pump chamber 55 surrounding the inlet port 13A to form an extended sealing area of the flap-type check valve when it is closed as shown. In this figure like numerals indicate features in common with Figures 1 1 and 12. A vent chamber 92, sealingly and securely attached to the second outlet (vent) port 14B of the pump chamber 55, comprises vent port 83, and encloses screen 91. The flexible (inlet valve) flap 41 is hingedly and securely attached to the inner wall 51 A by the stiff backing plate 45 and bolting means 46. The flexible flap 41 is also reinforced against pressure within the pump chamber 55 by the stiff members 44 and 42 fastened together by the fastening means 43 with the flexible (inlet valve) flap 41 sandwiched between them as shown. The pump is shown with the diaphragm 52 moving to discharge fluid through the open outlet check valve 31 A with the vent valve 30 also open. The flow restricting check valve 32 limits the flow rate of fluid discharging through vent valve 30, as described for Figure 12.

Figure 14 is a schematic showing a diaphragm pump 100 like that of Figure 13, fitted with the inlet check valve 31 of Figure 1 1 . The inlet port position 13A is similar to that of Figure 13. In this figure like numerals indicate features in common with Figures 1 1 and 13. Note that vent port 83C on the chamber surrounding the inlet check valve 31 is connected to inlet vent port 83A by conduit 83B, whereby air accumulating around inlet check valve 31 is vented to the pump chamber 55, and thereafter vented through vent port 83.

Figure 15 shows an enlarged detail 91 A of a section of the screen barrier 91 of Figures 1 1 to 14 wherein a plurality of slots 174 are the screen first apertures. The view is that "seen" by fluid approaching the screen from the pump chamber. In this example the screen is a thin sheet of perforated resilient material 172 wherein un -perforated regions of the screen are shown shaded, and support joists 173 and support bearers 171 (supporting the joists 173) are shown as dotted lines to indicate they lie under the screen 172. The screen 172 has a plurality of U-shaped slots 174 each having a cantilevered central strip 175 that is integral with the thin sheet 172 at one end only. The strip 175 is free to deflect resiliently as a cantilever away from the plane of the thin sheet and the supporting joists 173, thereby increasing the flow area for fluid flowing through the slots 174 from the joists side of the screen. When fluid flows forwardly (through the screen before flowing past the support joists 171 and bearers 173) the central strip 175 is supported by the joists 173 and deflection of the central strips 175 (and the width of the slots 174) is thereby restricted when fluid flows forwardly through the screen apertures towards the joists 173.

When fluid flows in the reverse direction through the screen each strip 175 is unsupported, and can lifted by the fluid thereby increasing the size of flow area through the slots to the second screen aperture size. This increase releases granules that have been ensnared by the previously narrower (first screen aperture size) slots.

In a first alternative example the U-shaped slots become rectangular holes; the strips 175 are omitted and replaced by resilient strips or bristles securely attached to the screen sheet 172 at one end only, with the free end of each strip 175 extended to rest upon the screen sheet. In this alternative the joists 173 and bearers 171 may be unnecessary: The strips 175 function as described above.

In a second alternative example the rectangular holes are wider and more than one strip bridges each rectangular slot with the gaps between adjacent strips providing the screen apertures. Screens of this kind are disclosed in PCT/AU2009/000401 .

Figure 16 shows a prior art (swing-type) check valve 32 modified to serve as a flow restriction means. These valves are shown in Figures 1 1 , 12, 13 and 14.

Figure 17 shows a scrap view of the check valve 32 of Figure 16 viewed from the direction of the arrow AB. In these figures the valve body 130 encloses a cavity in which a swinging flap disc 126 is suspended from a pivot 127, and rotates to open or close valve 32. When flow enters from the right-hand end 125 of Figure 16, the disci 26 lifts towards the position indicated by the ghost lines 128. When flow enters from the left- hand end 124, the disc closes onto the valve seat 131 , and flow through the valve 32 is restricted by the small aperture 129. Note that this small aperture is a notch having the shape of an inverted V with the base of the V lying at a periphery of the disc 126, wherein the width of the notch increases with depth through the thickness of the disc towards the seat 131 in Figure 16. This geometry allows particles trapped within or against the small aperture to be flushed clear when flow enters from the right-hand end 125, and swings open the check valve flap.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the examples without departing from the spirit or scope of the invention as broadly described. The present embodiments and examples are, therefore, to be considered in all respects as illustrative and not restrictive. The materials from which the flexible tube or sheet are constructed will preferably be a flexible and fatigue resistant elastomeric material such as a synthetic or natural rubber, and a knitted, or woven and bonded ligaments, or bonding-compatible, tensile strength resistant, abrasion and fatigue resistant fabric may be used where an embedded or attached reinforced fabric is required. Elsewhere metals or stiff fibre-reinforced plastics may be used. The flexible tube or sheet may consist of more than one layer. It may be formed from appropriate tubular material, or from flat natural or synthetic rubber tube or sheet or other suitable elastomeric material in contiguous loose, or bonded, layers, to reduce vulnerability to failure by puncture, without sacrificing flexibility: the inner layers may be made of a softer, abrasion-resistant material or even coated with PTFE.