Abstract:
A compact system is provided for diverting excess flow of liquid such as waste water from a conduit and to retain debris within the conduit. This incorporates a control section ( 22 ), which may be generally cylindrical, and arranged to be rotatable about a longitudinal axis ( 23 ), and defining a discharge port ( 24 ) through which excess water can leave the conduit. In operation, the depth of water in the conduit would be measured ( 15 ) downstream of the control section ( 22 ), and the rotation of the control section ( 22 ) adjusted in accordance with whether the water surface is above or below a depth limit. The discharge port ( 24 ) may include a grille to retain any debris, and the apparatus may include brushes ( 27 ), scrapers ( 29 ) or water jets ( 26 ) to dislodge any material held on the grille when the discharge port is at a top centre position.

Description:
[0001]    The present invention relates to a method and an apparatus for diverting flowing liquid from a conduit, for example if there is an excess of flow along the conduit. 
         [0002]    In this field, which is particularly relevant to the control of waste water, some exemplary devices are described in: 
         [0000]    “Device for removing debris from a flowing sewage liquid” EP0259547, Huber, Hans-Georg 
       “Rotary Screen” 
     GB2241905, Eden, Keneth Albert 
       [0003]    “Sewage flow control system” 
       KR20020057668, Lee, Gwon Jae 
       [0004]    Wastewater flowing in drains and sewers often becomes combined with rainfall. In periods of heavy rainfall, the additional volume flowing in these conduits may exceed their capacity. When this happens, a portion of the flow must be diverted from the conduit to prevent wastewater backing and emerging from entry points and at manholes. Excess flow is diverted from the conduit into a nearby watercourse such as a river or canal. 
         [0005]    A system for diverting excess flow in a sewer is called a sewer overflow. They are required to keep debris, especially floating material, within the sewer, and not allow such material to reach natural watercourses. This can be done by mechanical screens but this requires motorised equipment. 
         [0006]    Conventional sewer overflows take the form of a spill-crest running horizontally along a length of the conduit at a level of typically 0.8 times the drain diameter above the invert of the drain (i.e. the lowest level in the drain). This causes the flow to spill from the drain when its level exceeds 0.8 times the diameter. Debris is mechanically screened in a spillway and returned to the drain to pass downstream with the retained flow. From the spillway, the excess flow discharges into the overflow channel leading to, for example, a river. This arrangement requires long crests to allow large volumes to be diverted with the limited head available in the conduit above the crest. 
         [0007]    Although simple, these conventional systems have drawbacks: 
         [0000]    1. They occupy a significant length of sewer. Sewers are normally underground and therefore, to install them is costly.
 
2. The arrangements for screening and returning debris to the sewer are elaborate and prone to failure.
 
3 The scope for control of the flows is determined by the cost which usually means that conventional systems can divert a limited portion of excess flow. These systems can be overwhelmed by storm surges.
 
         [0008]    An active system incorporates a motorised gate to allow a higher portion of the flow to be diverted. The conduit cross-section is adapted to a rectangular section. The motorised gate is installed on a vertical wall of the rectangular section. Controlled sewer overflows require a means of measuring the depth of water downstream of the gate so that the gate position can be continuously varied to limit the downstream depth to a predefined level. 
         [0009]    Sewers running at near-full capacity are designed to have flow velocities of 0.8 to 1.0 m/s which usually means the hydraulic conditions are close to a critical state determined by a parameter known as the Froude number. At the critical state, small disturbances of the water surface in the channel can cause significant variations in the capacity of the conduit. Furthermore, as the water level approaches the roof of the drain, the flow capacity diminishes: maximum capacity occurs at 94% of the diameter. This induces a further mode of instability in which the flow alternates with surging oscillations. Such oscillations cause problems in controlling the gate position. These conditions make the measurement of downstream depth in the conduit technically difficult. Unless water level can be measured reliably, control of the flow cannot be assured. 
         [0010]    The object of this invention is to achieve a compact system for diverting excess flow in wastewater conduits to provide precise and stable control, and to retain debris within the conduit. 
       SUMMARY OF THE INVENTION 
       [0011]    The above and other objects of the invention are achieved by a control section of conduit arranged to rotate about an axis, the control section communicating with upstream and downstream portions of the conduit and supported for rotation about an axis, the control section defining a discharge port through which liquid such as water may be discharged from the conduit. 
         [0012]    The method comprises determining the flow of the liquid in the conduit to determine if the flow is above or below a flow limit, and: 
         [0013]    if the flow of liquid is above the flow limit, causing the control section to rotate about the axis to move the discharge port to progressively lower positions to cause liquid to commence discharge from the conduit or to increase the discharge of liquid from the conduit; 
         [0014]    if the flow of liquid is below the flow limit, causing the control section to rotate about the axis to move the discharge port to progressively higher positions to cause the discharge of liquid from the conduit to be reduced or to cease. 
         [0015]    If the flow or depth of liquid (e.g. water) persists at a level below a flow or depth limit, the method may involve causing the control section to rotate about the axis to a parked position at which the discharge port is at the top of the control section. 
         [0016]    The discharge port preferably incorporates a grille of bars to prevent any debris carried by the water being discharged, and the method preferably comprises periodically moving the control section to this parked position, in which the discharge port and so the grille is at the top of the control section, to allow any debris on the grille to fall back into the water flowing in the conduit. 
         [0017]    In a further modification two or more such control sections may be arranged in series, and may be controlled by a common controller. For example when one control section is in the parked position to allow trapped debris to fall back into the liquid in the conduit, the other control section may be moved into the outflow position, so that there is no buildup of water level in the conduit. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0018]    The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which: 
           [0019]      FIG. 1   a  shows a perspective view of a conventional system for limiting a flow of water in the conduit; 
           [0020]      FIG. 1   b  shows a cross-sectional view of the system shown in  FIG. 1   a;    
           [0021]      FIG. 2   a  shows a perspective view of a prior art system with an actuated gate; 
           [0022]      FIGS. 2   b  &amp;  2   c  show sectional views of the system of  FIG. 2   a  with the gate in the closed and open positions, respectively; 
           [0023]      FIG. 3  shows a perspective view of a system in accordance with the invention with a control section of the conduit that can be rotated about an axis; 
           [0024]      FIGS. 3   a  to  3   e  show cross-sectional views of the control section of the system of  FIG. 3  at different degrees of rotation 
           [0025]      FIG. 3   f  shows a perspective view of the system of  FIG. 3  with the control section in a different position; 
           [0026]      FIG. 4  shows a modification to the system of  FIG. 3  with grille and grille-cleaning brushes and with nozzles for water-jet back-flushing of the grille; 
           [0027]      FIGS. 4   a  to  4   e  show cross-sectional views of the arrangement of  FIG. 4  at different degrees of rotation; 
           [0028]      FIG. 5  shows a cross-sectional view of an alternative modification to the system of  FIG. 3  with grille and grille-cleaning scraper and with nozzles for water-jet back-flushing of the grille; and 
           [0029]      FIGS. 5   a  to  5   f  show cross-sectional views of the arrangement of  FIG. 4  at different degrees of rotation. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0030]    Referring to  FIGS. 1   a  and  1   b , there are shown sections of a conduit of circular cross-section for carrying wastewater with an upstream section  1  and a downstream section  2  of the conduit between which there exists a control section  3  with a horizontal discharge crest  4  and with discharge chute  5  to carry any discharged wastewater to a spillway  6  which then leads the discharge to a receiving watercourse, not shown, such as a river or canal. The discharge crest  4  is at an elevation E above the invert line  7  of the conduit (that is to say the bottom of the conduit). 
         [0031]    Water flowing along the conduit at a level H 1  relative to the invert line  7 , remains in the conduit because it is below the discharge crest  4 . If the water level rises to H 2  above the crest elevation E then a portion of the flow from the upstream section  1  will be discharged over the crest  4 . This discharge is related approximately by: 
         [0000]      Discharge= KL ( H 2 −E ) 1.5    
         [0000]    where L is the horizontal length of the crest and K is a constant. 
         [0032]    The surface of the water  8  drops as the flow passes along the crest  4 . This means that that this type of system can only limit the water level approximately in the downstream section  2  because the discharge decreases asymptotically as H 2  decreases along the discharge crest  4 . In practice, the crest length, L, is made as long as possible, subject to cost limitations. Often, two discharge crests are constructed on opposite sides of the drain with separate chutes leading the discharges to a common spillway below the conduit. 
         [0033]    Referring now to  FIGS. 2   a ,  2   b  and  2   c , these show a drain overflow system with an actuated gate. The conduit has an upstream section  1  and a downstream section  2  with a rectangular chamber at a control section  13 . An actuated gate  14  is located in a vertical side wall  11  of the control section  13  and is incorporated in a penstock frame  12 . The gate  14  is raised vertically to allow water to flow underneath it. In an alternative, the gate  14  might instead be lowered vertically to allow excess water to flow over it. 
         [0034]    A sensor  15  is located close to the downstream section  2  to monitor the level H 2  of the water surface  8 . The type of sensor  15  shown in  FIG. 2   a  and is an air-ranging ultrasonic level measurement sensor. A signal representing the water level is communicated via line  16  from the sensor  15  to a control unit  17  which positions the gate  14  via the control line  19  to the actuator  18  according to the sensed water level H 2 . When the water level exceeds the required limit in the downstream section  2 , the control unit  17  causes the gate  14  to be gradually opened by a few millimetres by actuator  18 . When the water level falls below the required limit, E, the control unit  17  moves the gate  14  towards its closed position. 
         [0035]    This arrangement can be constructed in a much more compact form than that of  FIG. 1 , because there is greater control over the outflow rate. It therefore is more cost-effective especially when the system is to be installed underground. It also has the advantage of being able to regulate the water level to the predefined limit, E. 
         [0036]    Another arrangement, not illustrated herein, is often used at the inlet to sewage treatment works. This uses the conventional arrangement of  FIG. 1  but with an actuated gate in the conduit of the downstream section. This gate is normally fully open. It is partially closed when it is necessary to restrict the water level in the downstream section. This method has two disadvantages relative to  FIG. 2 : 
         [0037]    the water surface immediately downstream of the gate is severely disturbed by the turbulence caused by water flowing under the gate. The sensor  15  must therefore be located far downstream of the gate to ensure reliable measurement of H 2 ; and 
         [0038]    the water level in the upstream section  1  has to be higher than that which would be required by the arrangement of  FIG. 2 . This normally means that the full-bore of the drain is occupied by flowing wastewater. 
         [0039]    This induces cyclic instability making precise control of water level downstream impossible. 
         [0040]    Consequently this modification to the arrangement of  FIG. 1  with a control gate across the downstream conduit is not only inherently unstable, but would require the installation to occupy a much longer length of the conduit and would therefore be costly. 
         [0041]    Referring now to  FIG. 3 , this shows a control apparatus of the invention, incorporating a cylindrical control section  22  of the conduit which can be rotated about the axis  23  while supported in bearings  21 . The bearings  21  incorporate seals (not shown) to prevent leakage of water from the conduit. A discharge port  24  in the circumference of the control section  22  can be rotationally positioned about the axis  23  by a linkage  25  to an actuator  26 . In this example the upstream and downstream portions  1  and  2  of the conduit define a longitudinal axis that is co-linear with the rotational axis  23  of the control section  22 ; and in this example the discharge port  24  is rectangular, with its long axis parallel to the axis  23 , and subtending an angle of about 60° from the centre of the cylindrical control section  22 . 
         [0042]    Flanges  27  couple to spigots on upstream and downstream sections  1  and  2  of the conduit. The flanges  27  form part of a chassis  28  on which the actuator  26  is mounted. The flanges  27  couple with the stationary member of the bearings  21  and the cylindrical control section  22  couples with the rotating member of the bearings  21 . Movement of the actuator  26  causes the cylindrical control section  22  to turn around the axis  23 , by which the discharge port  24  can be positioned at any circumferentially higher or lower position  24   c  (as shown in  FIG. 3   f ). To direct discharge from the port  24  to a spillway  6 , a chute  5  is affixed to the cylindrical control section  22 . 
         [0043]    In this example the upstream and downstream sections  1  and  2  of the conduit are cylindrical, and of the same diameter as the cylindrical control section  22 ; the connections between the flanges  27  and the upstream and downstream sections  1  and  2 , and the bearings  21 , do not protrude into the cylindrical flow path, so the flow path for the liquid is a continuous cylindrical channel without any steps at which debris might be trapped. A further benefit of providing a continuous cylindrical channel of uniform bore for the flowing liquid is that the flow is more stable. 
         [0044]    A sensor  15  is located in the downstream section  2  to monitor the water level H 2 . A signal representing the water level is communicated via line  16  from the sensor  15  to a control unit  17  which positions the cylindrical control section  22  by the actuator  26  according to the sensed water level H 2 .  FIGS. 3   a  to  3   e  show sectional views of the control section  22  at different angular positions. 
         [0045]    The port is normally parked near to the top-centre position, as shown in  FIG. 3   e , when the water level H 2  is below E. When the water level reached or exceeds the limit E, as illustrated in  FIG. 3   a , the controller  17  inches the actuator  26  to rotate the control section  22  and to move the discharge port  24  to a lower position to discharge excess flow from the conduit via the discharge port  24 , as shown in  FIGS. 3   b  and  3   c . Typically the discharge port  24  would be moved in increments of a few millimetres, for example each increment may be less than 10 mm, for example 3 mm or 5 mm, and such a movement would be made in accordance with a measurement of the water level at regular intervals for example every minute or every two minutes (indeed such measurements may be made more frequently if the water level is observed to be close to the required limit). When the water level falls below the required limit, the controller  17  inches the actuator  26  to rotate the control section  22  and so to raise the discharge port  24  to a higher position to reduce the discharge, as illustrated in  FIG. 3   d.    
         [0046]      FIG. 4  shows a modification to the system of  FIG. 3  with a grille of bars  25  across the discharge port  24  to prevent or inhibit debris from being discharged through the discharge port  24 . However, such screens can become blocked by excessive accumulation of debris. A clearing cycle is therefore used to remove any such accumulation. The control section  22  is periodically rotated so that the discharge port  24  is at the top-centre position, as shown in  FIG. 4   a , where heavier material drops back into the flowing water to be carried downstream. Lighter material can be flushed off the grille by discharge water recirculated under pressure through nozzles  26  as shown in  FIG. 4   d . The flushing action is synchronised with the return of the discharge port  24  to the top-centre position, as shown in  FIG. 4   e . The interval between such actions may be a fixed period, such as 5 minutes. However, the period may also be determined by the amount of blockage, indicated by the position of the discharge port  24 . A blocked grille would cause the control unit to move the discharge port  24  to its lowest position, a position detectable by a limit switch (not shown) connected to the control unit. In such an event, the control unit would initiate a clearing cycle. 
         [0047]    In a further modification, the system may include two such control sections  22  arranged in series, and both these control sections  22  may be controlled by the same controller  17 . If the water level exceeds the desired limit E (as shown in  FIG. 3   a ), then one or other of these control sections  22  would be actuated as described above. When one control section  22  is undergoing a clearing cycle as described in relation to  FIG. 4   a , then the other control section  22  would be actuated to allow discharge of the excess liquid. 
         [0048]    The greater part of the bars  25  forming the grille lie on circular arcs outside the cylindrical control section  22  and are centred on the axis of rotation  23 . The ends of the bars  25  of the grille are curved towards the axis  23  and are fixed to the control section  22  to allow members, such as fixed brushes or scrapers, external to the control section to extend inside the grille to clear it of debris as the control section  22  is rotated. In this example motorised brushes  27  may be used to clear debris from the grille as the discharge port  24  returns to the top-centre position as shown in  FIGS. 4   d  and  4   e . Preferably these motorised brushes  27  are used in conjunction with water under pressure sprayed through nozzles  26 . 
         [0049]      FIG. 5  shows a modification to the system of  FIG. 4  in which the motorised brushes  27  are replaced by scrapers  29  interposed between the bars  25  of the grille so that material adhering to the bars  25  is scraped off by the inclined leading edges  30  of the scrapers  29 , thence to fall towards the water surface  8 . 
         [0050]      FIG. 5   a  shows the system at the limit E prior to controlling the water level  8 .  FIGS. 5   b  and  5   c  show the cylindrical control section  22  rotated to induce discharge through the discharge port  24  thereby effecting control of the water level  8 .  FIGS. 5   d  and  5   e  show the cylindrical control section  22  rotated towards the top-centre position of the discharge port  24  in the to clear any debris from the grille  25 .  FIGS. 5   d  and  5   e  show an optional water jet nozzle  26  assisting the clearing of debris; and  FIG. 5   f  shows the system at a parked position. 
         [0051]    It will be appreciated that the apparatus of  FIG. 3  and the modifications of  FIGS. 4 and 5  are shown by way of example only. The control apparatus may be modified in various ways while remaining within the scope of the invention. For example the control section  22  is shown as being generally of circular cross-section, but it might instead be of generally elliptical cross-section or of U-shaped cross-section; the control section is described as defining a rectangular discharge port  24 , but the discharge port might instead be of generally elliptical shape.