Abstract:
A duck beak valve and/or pumps/pump systems that use such a valve are disclosed. The valve may include a flexible tube having an inlet portion and an outlet portion and a spigot having a spigot inlet portion and a spigot outlet portion. The inlet portion of the flexible tube is sealed relative to the spigot. Inner surfaces of the flexible tube outlet portion downstream of the spigot outlet portion close together when the valve is closed. At least one reinforcement engages the flexible tube and is adapted to pivot at an inlet end so that an outlet end of the reinforcement moves toward and away from a centerline of the flexible tube. The reinforcement reinforces the flexible tube against an externally applied backpressure when the outlet end of the reinforcement is disposed toward the centerline and the valve is closed.

Description:
[0001]    This application is a divisional of application Ser. No. 11/911,115, filed 10 Oct. 2007, which is a §371 national phase of PCT/AU2006/000482, filed 11 Apr. 2006, which claims priority from Australian Provisional Patent Application No. 2005901805 entitled “A slurry valve and applications” filed 12 Apr. 2005 and from Australian Provisional Patent Application No. 2005902616 entitled “FT valves and applications” filed 23 May 2005, the entire contents of all of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This invention relates to improvements in valves and pumps; in particular to improvements in pinch valves and to an improved pump incorporating features of such an improved valve. 
         [0003]    A pinch valve typically consists of a flexible resilient cylindrical elastomeric sleeve disposed in a valve body in the form of a continuous tube, sleeve or the like, together with a means to constrict the sleeve so as to control or stop the flow of fluid through the pipe. Typically the sleeve is concentrically located within a rigid outer valve housing and suitable means are provided to impress a fluid under pressure between the sleeve and the rigid valve housing so that the sleeve is squeezed inwards and deformed or collapsed to provide a restricted fluid flow passage. The impressed fluid is typically a gas or liquid under pressure. When that pressure is released, the resilience of the elastomeric tube is relied upon to open the valve. The elastomeric sleeve typically comprises a fabric reinforcement embedded in synthetic rubber to support the valve closure against the introduced pressure. Higher valve delivery pressure capacity and the need for adequate resilience in the tube to induce suction at the valve inlet when opening, require increasing layers of fabric reinforcement and increased wall thickness for the tube. This leads to a consequent loss of flexibility to the point where the required wall thickness may become impractical for use as a pinch valve. 
         [0004]    A duck-beak valve is a check valve form of the pinch valve that is closed in its relaxed condition with the outlet end of the sleeve unattached to the valve body. The fluid transiting the valve surrounds the inside and the outside of the sleeve, which opens when the valve inlet pressure sufficiently exceeds the valve outlet pressure. 
         [0005]    The alternative use of flap type check valves have the problem that they are vulnerable to being held open by the entrapment of solids between the flap and the valve seat. 
         [0006]    Thus, while a number of valve designs have been proposed, there remains a need for alternative designs. 
         [0007]    It should be noted that any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
       SUMMARY 
       [0008]    The present invention provides an improved duck beak valve and pumps and/or pump systems that use such a valve. In one embodiment, the duck beak valve comprises a flexible tube having an inlet portion and an outlet portion and a spigot comprising a spigot inlet portion and a spigot outlet portion. The inlet portion of the flexible tube is sealed relative to the spigot. Inner surfaces of the flexible tube outlet portion downstream of the spigot outlet portion close together when the valve is closed. At least one reinforcement engages the flexible tube and is adapted to pivot at an inlet end so that an outlet end of the reinforcement moves toward and away from a centerline of the flexible tube. The reinforcement reinforces the flexible tube against an externally applied backpressure (higher pressure at the outlet end of the valve than at the inlet end of the valve) when the outlet end of the reinforcement is disposed toward the centerline and the valve is closed. 
         [0009]    The spigot outlet portion may comprises one or more inclined surfaces against which the flexible tube abuts when the valve is closed in the presence of backpressure. The reinforcement may be a stiff member and may further comprise stiff plate disposed outwardly of the flexible tube and coupled to move therewith. The reinforcement may comprise a plurality of reinforcing spokes disposed in the flexible tube. The reinforcing spokes may comprise bars with ball-joint elements at one end thereof that pivot in corresponding sockets associated with the spigot outlet portion. A shoe may be associated with each reinforcing spoke, with the shoe moving with the corresponding spoke and the flexible tube. The shoe may be disposed between a tip of the corresponding spoke in the outlet direction and the flexible tube. The optional shoes provide an enlarged area over which forces from an externally applied backpressure are distributed when the valve is closed. Clamps may be provided that bias the outlet portion of the flexible tube to a closed position, with the clamps clamping each lateral side of the flexible tube together, but allowing expansion of the central part of the tube. 
         [0010]    The various aspects of the various embodiments may be used alone or in any combination, as is desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic side view of a valve, partly shown in cross section. 
           [0012]      FIG. 2  is an end view in cross section of the valve of  FIG. 1  in the directions of the arrows X-X. 
           [0013]      FIG. 3  is an alternative end view in cross section of the valve of  FIG. 1  in the direction of the arrows X-X. 
           [0014]      FIG. 4  shows a side view in half cross section of an alternative embodiment of a check valve. 
           [0015]      FIG. 5  is an enlargement of the inlet section of  FIG. 4 . 
           [0016]      FIG. 6  is an end view in cross section looking in the direction of the arrows XX-XX of  FIG. 5 . 
           [0017]      FIG. 7  shows a side view in half cross section of a further embodiment of a check valve. 
           [0018]      FIG. 8  is an end view in cross section looking in the direction of the arrows YY-YY of  FIG. 7 . 
           [0019]      FIG. 9  is a side view in cross section of a reinforcement system for the inlet section of a valve. 
           [0020]      FIG. 10  is an enlargement of part of  FIG. 9 . 
           [0021]      FIG. 11  is an enlargement of another part of  FIG. 9 . 
           [0022]      FIG. 12  is a plan view of spokes and links shown in  FIG. 9 . 
           [0023]      FIG. 13  is an alternative part end in cross section on the arrows Y-Y in  FIG. 9  of some of the spokes of some spokes and links. 
           [0024]      FIG. 14  is a plan view from the direction of arrow U in  FIG. 13 . 
           [0025]      FIG. 15  shows an alternative to  FIG. 13 . 
           [0026]      FIG. 16  shows an alternative to  FIG. 14 . 
           [0027]      FIG. 17  is a side view part of which is shown in cross section of a valve having electromagnetically driven diaphragm for opening and closing the valve. 
           [0028]      FIG. 18  is a schematic diagram illustrating three valves arranged to function as a pump. 
           [0029]      FIG. 19  is a schematic drawing showing a valve installed in a sub-atmospheric pressure driven sewer pipe. 
           [0030]      FIG. 20  is a schematic drawing showing an alternative embodiment to that of  FIG. 19 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Referring to the drawings,  FIG. 1  shows a side view in cross section of a check valve  10  sealingly bolted between an outlet pipe  2  and an inlet pipe  3 . The valve  10  comprises a hollow generally cylindrical housing in the form of a valve body  12  defining flanged ends  15  and  16 . A flexible tube  11  is shown in the closed position with flanged ends sealingly clamped between the faces of the flanges  15  and  16  at the inlet and outlet ends of the valve body respectively and the flanges  2 A of the outlet pipe  2  and  3 A of the inlet pipe  3 , as shown. The flexible tube  11  typically comprises a fabric reinforcement embedded in rubber although other materials could be used to provide the required degree of flexibility and fatigue resistance. It is to be noted that the outlet diameter  12 B or girth of the valve body  12  is greater than the inlet diameter or girth  12 A, with the diameter increasing at an angled step portion  12 C. 
         [0032]    As can be seen, an enclosed space  17  is formed between the outer walls of the tube  11  and the interior of the valve body  12 . Tubes  28 , controlled by valves  28 A and  28 B, are provided to allow fluid to enter, or be withdrawn from, the enclosed space  17  during servicing of the valve. However, it is to be noted that these valves  28   a  and  28   b  can be and are fully closed in use, to prevent ingress or egress of the fluid from the enclosed space  17 . The opening and closing of the valve  10  is not dependent on the entry or egress of fluid along the tubes  28 . 
         [0033]    In use, the enclosed space  17  is filled with a substantially incompressible non-volatile gas free liquid through pipes  28  and sealed.  FIG. 1  shows the valve in the closed position in which the flexible tube  11  is pinched closed and fluid is prevented from passing from the inlet  13  to the outlet  14 . Specifically, the tube is pinched and closed adjacent its inlet region  13  and expanded adjacent its outlet region  14  where the diameter of the valve body is greater and the flexible tube is expanded. 
         [0034]    When the pressure at the outlet  14  is larger than the pressure at the inlet  13 , the walls of the flexible tube adjacent the outlet  14  expand/are pushed outwards displacing the liquid in the enclosed spaced  17  towards the inlet and pinching or squeezing the walls of the flexible tube together adjacent the inlet. This state is shown in  FIG. 1 . However, when the pressure at the inlet  13  is larger than that at the outlet, the walls of the flexible tube in the inlet region  13  are forced outwards towards the valve body, and this displaces or pushes the liquid in the enclosed space towards the outlet  14 . However, the walls of the flexible tube are unable to close adjacent the outlet area  14  because the girth of the valve body and flexible tube is greater than that in the inlet region. Because the amount of liquid in the enclosed space remains unchanged the valve is opened, as shown in the ghost outline  11 A of the flexible tube. Thus a valve is provided which opens and closes automatically according to the differential pressure at the inlet and outlet of the valve. There are no moving parts. The valve does not require actuation and opens and closes solely based on the pressure differential. 
         [0035]    A first alternative to the enlargement of the girth  12 B of the flexible tube at the outlet is to have the length of the flexible tube in its outlet regions sufficiently longer than in its inlet regions so that the liquid displaced when the valve is opening does not close the outlet regions of the flexible tube, and for the walls in its inlet region (where the pinch occurs) to be to more flexible than elsewhere. A second alternative to the enlargement of the flexible tube girth is to construct the flexible tube so that in its relaxed state the flexible tube shape is the pinched shape of the fully closed flexible tube shown in  FIG. 1 . 
         [0036]      FIGS. 2 and 3  show two different end views in cross section of the check valve  10  of  FIG. 1  in the direction of arrows X-X. Like numerals indicate features in common with  FIG. 1 . 
         [0037]      FIG. 2  shows the flexible tube closed and flattened between two lobes. To accommodate this shape the body  12  is elliptical in the region of the flexible tube closure, which limits the range of locations for the lobes. To accommodate a range of lobe locations around the full circle the body shape in the region of the flexible tube closure has to be round as shown by the broken lines  12 B. 
         [0038]      FIG. 3  shows the flexible tube closed and flattened between three lobes to form a star shape. To accommodate this shape the body  12  needs be only slightly larger in diameter in the region of the flexible tube closure than the body diameter at the inlet  13  and outlet  14 . The lobes can be located anywhere around the circle, and the broken outline  11 B shows one alternative position. 
         [0039]      FIGS. 4 to 6  show an alternative check valve  100  in which like numerals indicate features in common with  FIG. 1 . In  FIGS. 4 to 6  the flexible tube  11  is a straight tube with parallel walls of larger bore than that of the inlet and outlet spigots  101  and  107 . The flexible tube  11  is typically formed from synthetic rubber and reinforced with a strong, but flexible, embedded woven fabric. The flexible tube  11  is sealingly clamped at its inlet and outlet ends around the spigots  101  and  107  by clamping straps  109  and  111 . The flexible tube is a “lay flat” tube that may be rolled up, but expands to a circular shape/cross-section when filled with liquid and comprises nitrile rubber reinforced with fine Dacron fibers, although as discussed below, other materials may be used for the flexible tube. 
         [0040]    The flexible tube  11  is narrowed over the squeezed section 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 center of the tube. This clamping of the sides biases the flexible tube flat with its inner walls pressed together over the clamped length as shown in  FIG. 6 , until the valve inlet pressure exceeds the valve outlet pressure sufficiently to open the valve. This arrangement also minimizes deformations of the tube as it flexes, and may thus extend the service life of the tube. Alternatively, stitching may be substituted for the clamping bars  105 . Note that the valve-open flow area through the clamped parts is reduced by the clamping bars  105 . 
         [0041]    The outlet end spigot  107  has a conical inlet, but the inlet end spigot  101  is cut as shown to provide flat surfaces  101 A that support the flexible tube against externally applied pressure when the valve is closed. 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 . Excursions towards flattening of the flexible tube  11  in its outlet regions is limited by the stiff tube  127 , which is perforated. 
         [0042]    Flange  15 , bolted cover plate  15 A and the securing nuts  113  allow the flexible tube to be sealingly encased within valve body  12 , and allow for easy dismantling for flexible tube replacements. A sealed screwed plug  114  allows access to the enclosed space  17  for adjusting the liquid inventory. 
         [0043]      FIGS. 5 and 6  also provide an example of an alternative duck-beak type of pinch valve wherein like numbered items obtain the same description as  FIG. 4 . 
         [0044]      FIGS. 7 and 8  show two half-flexible tube diaphragms  11 B and  11 C partly inflated with liquid so that when the check valve is closed (as shown) the two half-flexible tube diaphragms  11 B and  11 C are locally squeezed sealingly together downstream of the inlet  13  parts of the valve (to close the valve), and inflated upstream of the outlet  14  parts of the valve. The two half-flexible tube diaphragms  11 B and  11 C are sealingly clamped at each side of the flexible tube check valve between the flanges  119  and  119 A of the chamber inner walls  12 B and  12 C by the bolts  121 . 
         [0045]    When the flexible tube check valve  110  is open, the position of the upper half-flexible tube diaphragm is shown by the dotted lines  11 A (refer to  FIG. 8 ). The inlet and outlet ends of each half-flexible tube diaphragm  11 B or  11 C are sealingly clamped between the stiff conical insert  117  and the conical chamber inner walls  12 B and  12 C at the outlet  14 , and between the stiff conical insert  116  and the conical chamber inner walls  12 B and  12 C at the inlet  13 . Valves  28  (normally sealed) allow liquid to enter or be withdrawn from the sealed spaces  17 . These valves  28  can also allow the admission or extraction of fluid when the valve  110  is being used other than as a check valve. 
         [0046]    In  FIG. 8  the two half-flexible tube diaphragms  11 B and  11 C form an S shape in the closed position. Their shape in the open position is shown by the dotted lines  11 A. Like numerals indicate features in common with  FIG. 1 . 
         [0047]    As described for the check valve shown in  FIGS. 4 to 6 , the flexible tube immediately downstream of the inlet  13  must support the pressure at the outlet  14 , which is transmitted by the liquid in enclosed space  17 . In  FIG. 7  reinforcement is provided by a series of closely-spaced rods  21 A, embedded in the flexible tube  11 B and  11 C. Rods  21 A pivot within the flexible tube at their inlet end, where they are supported by the conical insert  116 . 
         [0048]      FIGS. 9 to 11  show a side view in cross section of the inlet section of a duck beak check valve or valve of  FIG. 1  where a reinforcing spokes and cage unit is inserted. 
         [0049]    In  FIGS. 9 to 11 , the reinforcing spokes  21  are round section steel bars with ball joint elements at both the inlet and outlet ends. Each spoke rotates about its ball  25  in a socket  26  located in the annular support ring  31 , and each spoke rotates towards the flexible tube axis when moving to the valve fully closed position (as shown), and rotates away from the flexible tube axis when opening to the full-open position shown by the ghost outline  11 A. The retaining ring  32  holds the balls  25  in their sockets  26 . The annular support ring  31  and its sockets  26  restrict the inlet end of the reinforcing spokes and cage unit  20  to a circular shape, but the other end of the cage unit  20  can adopt any shape not restricted by either the ligaments and cables  24 , or by the extension  31 A of the ring  31 , or the walls of the valve body  12 . 
         [0050]    Inwards rotation of any spoke past the axis when closing is restricted by the system of ligaments or cables  24 , and by the extension  31 A of the ring  31  on the inside of the spokes  21 . The length of each ligament or cable  24  is adjusted and fixed manually and anchored by an external device  34  before it begins operating. External devices  34  are located adjacent to the inlet and outlet ends of the flexible tube valve, and can be a device of the prior art such as the wedged rotatable posts used to adjust the tension in stringed musical instruments. Each ligament or cable  24  operates within a tubular sheath that protects the rubber parts of the flexible tube  11  from abrasion. The tubular sheath may be a wound tubular helix like those used in vehicle cable brake systems provided it does not itself overly restrict radial movements of the flexible tube. 
         [0051]    A collar  27  is pinned around each spoke at its inlet end, and a shoe  23  is attached to the other end of each spoke. Each shoe is attached to the ball end of its spoke by a “spring-closing” device as shown. The collar  27  and shoe  23  on each spoke  21  confine the links  22  to the region between the collar and the shoe  23 . 
         [0052]    Where  FIGS. 9 ,  10  and  11  provide an example of a duck-beak type of pinch valve the cable  24  and external device  34  are omitted. 
         [0053]      FIGS. 10 and 11  show an alternative conduit  24 A for the ligaments or cables  24  that passes through the spokes  21 . The two ends of each of these alternatively located ligaments or cables  24 A connect to similar external devices. Note that the tubular sheath and conduits for the ligaments and cables must provide adequate room for the ligaments or cables to squirm when the flexible tube is in its open position. Note also that an alternative cylindrical shape, or hinge may be substituted for the ball and socket pivots  25  and  26  shown. 
         [0054]      FIG. 12  shows a plan view of the spokes  21  and its cage in the flexible tube valve closed position. The bottom half of  FIG. 13  shows the links  22  that link any two adjacent spokes  21 . Each row of links link alternate pairs of spokes  21  to produce the “basket-weave” appearance shown. The top half of the plan view shows the spokes  21  with the links  22  removed, and provides an example of the rods  21  spaced within the fabric of the flexible tube without the addition of the links  22 . 
         [0055]      FIG. 13  is a part view in cross section on the arrows Y-Y in  FIG. 9  showing a system of links  22  attached to link pairs of spokes  21  as shown. Like numerals indicate features in common with all previous figures.  FIG. 14  is a plan view from the direction of the arrow U of  FIG. 13  of part of the cage  20  showing how the links  22  of  FIG. 13  are alternately positioned around successive pairs of spokes  21 .  FIGS. 15 and 16  provide details of alternative links  22 B that are woven around spokes  21 . 
         [0056]      FIG. 17  is a side view in cross section of a pinch valve  20 . Numbers that are common to  FIGS. 1 ,  2  and  3  indicate components that have basically the same function, and obtain substantially the same description provided above for  FIGS. 1 ,  2  and  3  except the girth of flexible tube  11  is substantially the same along its length. In  FIG. 17  a drive unit  30  is directly attached to the valve body  12  of a pinch valve, and enclosed space  17  is filled with gas-free hydraulic liquid. 
         [0057]    The electromagnetic drive mechanism  30  moves a diaphragm  86  that is sealingly clamped around its edges, between a flat surfaced flange  88  that extends from the valve body  12  around the periphery of the diaphragm  86 , and a stiff cover  87 . The diaphragm  86  is also clamped between two stiff plates  89  and  91  over its central regions as shown. The diaphragm  86  and the flange  88 , and mating parts can be circular, elliptical, obround, or rectangular when viewed from above in plan. 
         [0058]    Electromagnetically actuated solenoids  61 , attached by hinges  61 B to stiff plate  89  move diaphragm  86  towards the valve axis to close the valve, and away from the valve axis to open the valve. Appropriate energizing of the electromagnetic coils  62  moves both solenoids to close or open the valve. Each solenoid has a vertical slot  61 A that allows the solenoid to slide about a guide pin  92  that limits the vertical movement of the solenoid between the valve open and closed positions. Coils  62 , and pins  92  are securely attached to the cover  87  and space  103  is air filled and vented. 
         [0059]      FIG. 18  is a schematic showing a train of three pinch valves  1 A,  1 B and  1 C fastened sealingly to each other at their mating inlet and outlet ends, and to an inlet pipe  71  and an outlet pipe  72  to form a pump  60  having three pinch valves as its pumping elements. Items  74 ,  76  and  78  are mechanical-, electromagnetic-, hydraulic-, or pneumatic driven mechanisms that change the confines of the enclosed space within the valve body of each pinch valve (exemplified by  FIG. 17 ) to open or close it, or use the delivery or withdrawal of a gas or liquid into each enclosed space of a modified prior art pinch valve, to open or close it. 
         [0060]    A feature of pinch valves used in these trains is that the axial length of each flexible tube  11  is at least one third longer than their girth, and each flexible tube is constructed to be most responsive to closing or opening downstream of its inlet end and progressively less responsive towards its outlet end, so that, while the valve is closing, inlet regions of the flexible tube are biased to be pinched closed while its downstream parts are still closing, and while the valve is opening inlet regions of the flexible tube will be biased to open while its downstream parts are still opening. A programmed controller  84  controls when each of the said drive units delivers fluid under pressure to, or withdraws fluid from, each pinch valve to close, or open it as required. Links  81 ,  82  and  83  communicate commands from the controller  84  to each drive unit  74 ,  76  and  78 , (or where modified prior art pinch valves are used, deliver or release gas or liquid into or from enclosed space  17 ), in a sequence that opens or closes each of the pinch valves sequentially so that one of the pinch valves is at least part closed while parts of other valves in the train are open or opening. A sequence in which pinch valve  1 A, and/or pinch valve  1 B and/or pinch valve  10  are closed or closing (while pinch valve  1 B, and/or pinch valve IC and/or pinch valve  1 A respectively are opening or open) to provide a progressive induction of fluid into inlet  72 , and delivery of that fluid through the outlet  73  in a repeating cycle is: { 1 A closed,  1 B closing,  1 C open}; { 1 B fully closed,  1 C closing,  1 A opening}; { 1 C fully closed,  1 A open,  1 B opening}; { 1 A closing,  1 B open,  1 C opening), with the cycle repeated, wherein the positions within { } are instantaneous periods in each cycle. 
         [0061]    The train shown in  FIG. 18  can be extended mutatis mutandis, to use more than three pinch valves operating in a programmed sequence and any train may have a check valve inserted at its inlet, or its outlet, or at both its inlet and outlets. 
         [0062]      FIG. 19  is a schematic diagram showing an example of an air pressure closing pinch valve applied to a vacuum-driven sewer system  60  where, like numerals indicate features in common with  FIGS. 1 and 2 . Waste water or sewage flows by gravity into well  4  through the sewer pipe  5  and accumulates in the base of the well  4 . Tubes  27  and  28  connect the enclosed space  17  to the flow restricting valve  31  and the valve seat  23  at the top of float actuated valve unit  6 . Valve unit  6  comprises a float  22  that has a valve  24  attached to a stem  25  at its top. Flow-restricting device  31 , which can be a valve, or a tube of small bore, is placed between tube  27  and tube  29 , which connects to the interior of the sewer pipe  2  at a point downstream of pinch valve  1 A. Device  31  restricts the flow of air into conduit  29  induced by sub-atmospheric pressure in the sewer pipe  2 . Pinch valve  1 A opens when float  22  rises to level  33 , when valve element  24  enters seat  23  and seals conduit  27 . Air is withdrawn from conduits  27  and  28 , and enclosed space  17  through the flow restriction  31 , and pressure in the enclosed space  17  falls to the sub-atmospheric pressure within sewer pipe  2 . As result, the outer walls of the flexible sleeve  11  inflate and pinch valve  1 A opens: fluid can then flow freely through pinch valve  1 A into sewer pipe  2 . Periodic withdrawal of accumulated sewage from the well  4  into sewer pipe  2  is accomplished as follows. 
         [0063]    Sewage enters through sewer pipe  5  and collects in the base of the well  4  until accumulated sewage level rises from level  34  to level  33 . 
         [0064]    Float  22  floats up within confining cage  6 A with sewage accumulating in the well until valve  24  at the top of float  22  enters seat  23 , preventing further atmospheric air entering conduit  27 . Pressure in the enclosed space  17  falls towards the sewer pipe pressure and closed pinch valve  1 A re-opens. 
         [0065]    Sewage is withdrawn from the well into sewer pipes  3  and  2 , and the sewage level in well  4  falls towards level  34 . As the accumulated sewage level in well  4  falls, float  22  is suspended by both its buoyancy and the sub-atmospheric pressure in conduit  27 , which holds valve  24  in its seat  23 , until the increasing un-buoyed weight of the float overcomes the valve  24  suspension force and float  22  falls. Valve seat  23  opening is exposed, atmospheric pressure air enters conduits  27 ,  28  and  29  (but is throttled by flow-restricting device  31 ) and enclosed space  17 , walls of the flexible sleeve  11  are drawn together and pinched closed by the sewer sub-atmospheric pressure, pinch valve  1 A closes, and sewage ceases to be drawn from the well into the sewer pipe  3 . Further accumulation of sewage in well  4  raises level  34  to  33  and the cycle is repeated. 
         [0066]      FIG. 20  is a schematic diagram showing an example of the application of an air pressure driven pinch valve to a vacuum-driven sewer system  60 A where like numerals indicate features in common with  FIG. 19 . 
         [0067]    In this example the means of controlling the entry or exclusion of atmospheric air from conduit  27  comprises a tall dip-pipe  35 , which rises to a height above the expected maximum height (of the liquid column that can be supported by the expected minimum sub-atmospheric pressure in the sewer pipe  2 ), and remains submerged in the well  4  liquid until that level falls below level  34 . The open bottom of the dip-pipe  35  is set at the minimum acceptable level that accumulated sewage in well  4  can be permitted to reach. Tube  37  connects the space within the dip-pipe  35  to tube  27 . While the open bottom of the dip-pipe  35  remains submerged, liquid is drawn up into the dip-pipe  35  and pressure in the enclosed space  17  reaches and remains that of the sewer pipe  2 , and pinch valve  1 A remains open. Whenever the sewage level in well  4  falls below level  34 , it exposes the open end of dip-pipe  35 , atmospheric air enters dip-pipe  35  and enclosed space  17 , and pinch valve  1 A closes. 
         [0068]      FIG. 20  also shows (in ghost outline, with components indicated by the numbers  40 ,  41 ,  42  and  43 ) a prior art mechanically operated valve typical of those currently used in these sub-atmospheric pressure sewer systems. 
         [0069]    Whenever the valve  40  fails to close properly (typically due to obstruction by debris) the sewage liquid level in the well  4  falls below the level  34 , and the open bottom of the dip-pipe  35  is exposed. Sewage held in pipe  35  falls out, pressure in dip-pipe  35  rises to atmospheric, which transmits to tubes  37  and  27 , and pinch valve  1 A closes. Further influx of sewage into the well  4  (through the sewer pipe  5 ) increases the sewage level in the well from level  34  to level  33  when valve  40  opens releasing its obstruction, whereafter it continues periodically emptying well  4  until a further failure to close occurs. Manually operated valve  45  can be closed by servicing personnel to hold pinch valve  1 A closed during a manual clearing of the valve  40 . 
         [0070]    In the example shown there is potential for entrained liquid to be drawn into the said enclosed space of the pinch valve  1 A while liquid is falling within dip pipe  35 . To minimize this, liquid-from-air separating vessel  39 , and additional dip pipe  38  can be added as indicated. The bottom of the additional dip pipe  38  is placed slightly above the bottom of its neighboring pipe  35 , and becomes exposed before that of pipe  35 . When this occurs, air rises through dip pipe  38  while liquid falls in dip pipe  35 , and the separating vessel  39  (which may be a cyclone) minimizes entrainment of liquid into tube  37 . 
         [0071]    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 specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
         [0072]    For example, the flanged ends of the flexible tubes may be omitted and the inlet and outlet ends sealing secured around stiff short length tubes cut to support the duck beak shape or star shape of the flexible tube when closed. These short tubes could support reinforcements embedded in or attached to the wall of the flexible tube. 
         [0073]    The materials from which the flexible tube is 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 fiber-reinforced plastics may be used. 
         [0074]    The flexible tube may consist of several concentric flexible tubular layers. It may be wound from flat natural or synthetic rubber sheet or other sheet elastomeric material in several concentric boned layers, to reduce vulnerability to failure by puncture, without sacrificing flexibility, in which the inner layers may be made of a softer material or even coated with PTFE.