Abstract:
A check valve ( 10 ) comprises, a flexible tube ( 11 ) having first and second end portions defining an inlet ( 13 ) and an outlet ( 14 ), respectively, and a rigid valve body ( 12 ) surrounding the flexible tube ( 11 ). The end portions of the flexible tube are sealingly fixed to the valve body ( 12 ) to define an enclosed space ( 17 ) between the exterior of the flexible tube and the interior of the valve body. A fixed volume of a substantially incompressible fluid is located in the enclosed space ( 17 ). When the pressure at the outlet ( 14 ) is greater than the pressure at the inlet ( 13 ), the flexible tube is substantially collapsed so as to close the valve or allow severely restricted flow. However when the pressure at the inlet is greater than that at the outlet, some of the fluid is displaced from the inlet area towards the outlet area so that the flexible tube ( 11 ) is expanded in the area adjacent the inlet and the tube is substantially open. A pump based on a series of valves having some of the attributes of the check valve is also disclosed, as is a vacuum driven sewer system that incorporates a pinch valve.

Description:
[0001]    This application 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 which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to improvements in valves and pumps. In particular, it relates to improvements in pinch valves and to an improved pump incorporating features of such an improved valve. 
       BACKGROUND OF THE INVENTION 
       [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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    Thus, one object of the present invention to provide an improved valve in which less reliance is placed on the resilience of the elastomeric tube for opening the valve while at the same time retaining the tolerance of the pinch valve design towards entrapment of transiting particles without leaking. 
         [0008]    Subsidiary preferred objects relate to increasing the delivery pressure capacity of the pinch valve, with less sacrifice of the tube&#39;s flexibility. 
         [0009]    Other preferred aspects of the invention relate to the adaptation of the pinch valve as a check valve and as a component of a pump. 
         [0010]    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 OF THE INVENTION 
       [0011]    A first broad aspect of the present invention provides a valve comprising: 
         [0012]    a flexible tube having first and second end portions defining an inlet and an outlet, respectively; 
         [0013]    a rigid valve body surrounding the flexible tube, the end portions of the flexible tube being sealingly fixed to the valve body to define an enclosed space between the exterior of the flexible tube and the interior of the valve body; and 
         [0014]    a fixed volume of a substantially incompressible fluid located in the said enclosed space; and wherein 
         [0015]    the arrangement being such that when the pressure at the outlet is greater than the pressure at the inlet, the flexible tube is substantially collapsed so as to close the valve or allow severely restricted flow, and wherein when the pressure at the inlet is greater than that at the outlet, some of the fluid is displaced from the inlet area towards the outlet area so that the flexible tube is expanded in the area adjacent the inlet and the tube is substantially open. 
         [0016]    In a preferred embodiment the girth of the outlet of the flexible tube is greater than the girth of the inlet of the flexible tube. 
         [0017]    The valve body may be substantially cylindrical and the diameter of the valve body at the outlet may be greater than the diameter of the valve body at the inlet. 
         [0018]    When the pressure at the valve outlet is larger than the pressure at the valve inlet the walls of the flexible tube at the outlet are pushed outwards displacing liquid towards the inlet and pinching or squeezing the walls of the tube together at the inlet region to close the valve. However, when the valve inlet pressure is larger than that of the outlet the walls of the flexible tube expand outwards at the inlet area displacing liquid towards the outlet. Since the girth of the tube in its outlet region is larger than the girth in the inlet region and because there is a fixed volume of incompressible fluid between the valve body and the flexible tube, the valve opens. 
         [0019]    In one embodiment, the walls of the tube in a region adjacent the inlet are preferably more flexible than its walls in a region adjacent its outlet, and the length of the flexible tube is longer in its outlet region than in its inlet region. 
         [0020]    The tube may comprise two or more part tubes fixed together by clamping, or other suitable means to define a tube. 
         [0021]    Preferably, reinforcing spokes are defined in the flexible tube adjacent the inlet and/or outlet of the valve. 
         [0022]    The spokes may comprise round section steel bars with ball joint elements at the inlet and/or outlet ends. 
         [0023]    In a preferred embodiment, a retaining ring is defined at the inlet and/or outlet and holds the ball joint elements in sockets so as to restrict the ring end of the reinforcing spokes to a circular shape. 
         [0024]    In a second aspect, the present invention provides a pump comprising a series of valves, 
         [0025]    said valves comprising 
         [0026]    a flexible tube having first and second end portions defining an inlet and an outlet, respectively, said flexible tube having a length that is at least one third longer in its axial length than its girth; 
         [0027]    a valve body surrounding the flexible tube, the end portions of the flexible tube being sealingly fixed to the valve body to define an enclosed space between the exterior of the flexible tube and the interior of the valve body; and 
         [0028]    a fixed volume of a substantially incompressible fluid located in the said enclosed space; and 
         [0029]    actuator means for applying increased pressure to the volume of the fluid thereby compressing the flexible tube and means for activating said actuator means; 
         [0030]    and wherein 
         [0031]    a plurality of such valves linked in series end to end without obstructions therebetween; 
         [0032]    and control means are provided to operate the actuator means of each valve in sequence such that the valves may be opened and closed in a controlled sequence with an upstream end of the series opening or closing first to define a closed portion due to compression of the flexible tube with the closed portion progressing downstream. 
         [0033]    Typically there will be at least three valves in series. The actuator of the valves may include a flexible diaphragm. 
         [0034]    In a third aspect, the invention provides, a system for the periodic withdrawal of sewage or waste water into a sewer system, operating at sub-atmospheric pressure, from a well in which waste water accumulates using a flexible tube type pinch valve wherein; 
         [0035]    an exit pipe depends into the well for the egress of said liquids or liquid/solid mixtures from the pit, flow through the exit pipe being controlled by the flexible tube type pinch valve, the exit pipe having an inlet located inside the well 
         [0036]    and the enclosed space between the exterior of the flexible tube and the interior of the valve body of the pinch valve is connected to both a first conduit depending into the waste water in the well and a second conduit connected to the sub-atmospheric pressure of the sewer system downstream of the pinch valve; 
         [0037]    wherein the second conduit includes a flow restriction means, whereby air at atmospheric pressure is prevented from entering the enclosed space of the pinch valve when the open end of the first conduit is submerged in the waste water, thereby exposing the enclosed space to sub-atmospheric pressure which holds the pinch valve open, 
         [0038]    and when the waste water level in the well falls and exposes the open end of the first conduit atmospheric pressure air enters the enclosed space and is throttled by the flow restriction means, which causes the pressure in the enclosed space to rise to atmospheric, closing the pinch valve. 
         [0039]    In an alternative to the third aspect, the base of the first conduit is not submerged, but is closed by a valve from which a float depends, 
         [0040]    whereby when the waste water level in the well falls below the level at which the buoyancy of the float combined with the sub-atmospheric pressure force holding the valve closed is sufficient, the float falls, opening the valve, air enters the first conduit and the pinch valve opens, 
         [0041]    and when the waste water level in the well rises it lifts and closes the valve and the pinch valve closes; 
         [0042]    thereby opening the pinch valve when the waste water level attains its high level, and remaining open until the waste water level re-attains its low level. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0044]      FIG. 1  is a schematic side view of a valve, partly shown in cross section; 
           [0045]      FIG. 2  is an end view in cross section of the valve of  FIG. 1  in the directions of the arrows X-X; 
           [0046]      FIG. 3  is an alternative end view in cross section of the valve of  FIG. 1  in the direction of the arrows X-X; 
           [0047]      FIG. 4  shows a side view in half cross section of an alternative embodiment of a check valve; 
           [0048]      FIG. 5  is an enlargement of the inlet section of  FIG. 4 ; 
           [0049]      FIG. 6  is an end view in cross section looking in the direction of the arrows XX-XX of  FIG. 5 ; 
           [0050]      FIG. 7  shows a side view in half cross section of a further embodiment of a check valve; 
           [0051]      FIG. 8  is an end view in cross section looking in the direction of the arrows YY-YY of  FIG. 7 ; 
           [0052]      FIG. 9  is a side view in cross section of a reinforcement system for the inlet section of a valve; 
           [0053]      FIG. 10  is an enlargement of part of  FIG. 9 ; 
           [0054]      FIG. 11  is an enlargement of another part of  FIG. 9 ; 
           [0055]      FIG. 12  is a plan view of spokes and links shown in  FIG. 9 ; 
           [0056]      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; 
           [0057]      FIG. 14  is a plan view from the direction of arrow U in  FIG. 13 ; 
           [0058]      FIG. 15  shows an alternative to  FIG. 13 ; 
           [0059]      FIG. 16  shows an alternative to  FIG. 14 ; 
           [0060]      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; 
           [0061]      FIG. 18  is a schematic diagram illustrating three valves arranged to function as a pump; 
           [0062]      FIG. 19  is a schematic drawing showing a valve installed in a sub-atmospheric pressure driven sewer pipe; and 
           [0063]      FIG. 20  is a schematic drawing showing an alternative embodiment to that of  FIG. 19 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0064]    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. 
         [0065]    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. 
         [0066]    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 . 
         [0067]    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 . 
         [0068]    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. 
         [0069]    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. 
         [0070]    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 . 
         [0071]    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. 
         [0072]    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. 
         [0073]    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. 
         [0074]    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 . 
         [0075]      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 . 
         [0076]      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. 
         [0077]      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. 
         [0078]      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 . 
         [0079]    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 centre 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 minimises deformations of the tube as it flexes, and may thus extend the service life of the tube. 
         [0080]    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 fibres, although as discussed below, other materials may be used for the flexible tube. 
         [0081]    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 . 
         [0082]    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 . 
         [0083]    Excursions towards flattening of the flexible tube  11  in its outlet regions is limited by the stiff tube  127 , which is perforated. 
         [0084]    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. 
         [0085]      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 . 
         [0086]      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 . 
         [0087]    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. 
         [0088]    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 . 
         [0089]    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 . 
         [0090]      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. 
         [0091]    Key elements in  FIGS. 9 to 11  are the reinforcing spokes  21 , which 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 . 
         [0092]    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. 
         [0093]    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. 
         [0094]    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 . 
         [0095]    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. 
         [0096]      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. 
         [0097]    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. 
         [0098]      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 . 
         [0099]      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. 
         [0100]      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 . 
         [0101]      FIGS. 15 and 16  provide details of alternative links  22 B that are woven around spokes  21 . 
         [0102]      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. 
         [0103]    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. 
         [0104]    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 energising of the electromagnetic coils  62  moves both solenoids to close or open the valve. 
         [0105]    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. 
         [0106]      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. 
         [0107]    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  1 C 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: 
         [0108]    { 1 A closed,  1 B closing, IC 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. 
         [0109]    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. 
         [0110]      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 . 
         [0111]    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 . 
         [0112]    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 SUBSTITUTE SHEET (RULE  26 ) 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. 
         [0113]    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 . 
         [0114]    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. 
         [0115]    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. 
         [0116]      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 . 
         [0117]    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 . 
         [0118]    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 . 
         [0119]    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. 
         [0120]    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. 
         [0121]      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. 
         [0122]    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. 
         [0123]    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 . 
         [0124]    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 minimise 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 neighbouring pipe  35 , and becomes exposed before that of pipe  35 . 
         [0125]    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) minimises entrainment of liquid into tube  37 . 
         [0126]    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. 
         [0127]    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. 
         [0128]    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 fibre-reinforced plastics may be used. 
         [0129]    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.