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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under 35 U.S.C. §371 of International Patent Application PCT/AU2014/000711, filed Jul. 11, 2014, designating the United States of America and published in English as International Patent Publication WO 2015/003217 A1 on Jan. 15, 2015, which claims the benefit under Article 8 of the Patent Cooperation Treaty to Australian Patent Application Serial Nos. 2013903986 filed Oct. 6, 2013, 2013902805 filed Jul. 29, 2013, and 2013902571 filed Jul. 12, 2013. 
     TECHNICAL FIELD 
     This disclosure concerns flow control valves for immersion in channels of the type built for irrigation. 
     BACKGROUND 
     Irrigators rely on channels for delivery of water to areas where crops are grown. Such areas may have a laser-levelled surface so that an inbuilt incline ensures the water runs to the end of the channel whenever water is available. 
     When a head develops in the water supply network, the end of the channel overflows. If this continues, the ground surrounding the overflow site becomes muddy and the roots of the growing crop lack air and die. The grower loses a percentage of the crop and the muddy area is an obstacle to the free movement of the wheels of irrigation equipment. 
     The flow in the channels is ensured by bulk water delivered to the channels through pipes. In related Australian Patent Serial No. 2013902571, float-operated valves are described that include a rise and fall stop gate capable of stopping flow in the pipe supplying an installation such as a LINDSAY® overhead irrigation device. 
     U.S. Pat. No. 1,343,871 describes a system for supplying water to different parts of a field by a pipe that fills a group of containers, each with its own float valve to allow water to flow to subsidiary boxes. A ball float on the end of an arm that progressively closes a valve to a valve seat stopping the flow is out of sight inside the container. 
     U.S. Pat. No. 2,362,747 describes a chain of tanks, each with an outlet for discharge into a soil channel. A control tank in the chain contains a float valve that opens and closes a valve in a pipe that supplies the whole chain. 
     U.S. Pat. No. 6,953,156 describes a system for irrigating sloping land. This too relies on a ball-type float valve that controls water entry into a distributor tank from which branch pipes flow to different areas depending on their slope. 
     The ball valves used for these systems cannot be inspected and maintained easily. 
     BRIEF SUMMARY 
     The apparatus aspect of the disclosure provides a stop valve for a duct pipe feeding an irrigation channel comprising a duct with an inlet and an outlet, a rise and fall gate between the inlet and outlet, a pair of float arms supported on pivots lying on an axis transverse to the duct direction and a float for determining the inclination of each float arm. 
     The duct may be linear with the gate at 90 degrees to the duct axis. The gate may have static guides that are wider than the inlet portion of the valve body and a flat gate that slides in the guides between an open position clear of the inlet portion and a closed position in which the gate lies in register with the inlet portion, thereby preventing flow. 
     The float arms may be rods that are free to rotate about the pivots, attached at one end to the rise and fall gate plate and at the opposite end to the float. The float may be spaced from the end of an aim by a rigid link. 
     Thus, when the floats ascend, the arms rotate to an inclined position in which the gate is drawn downward to its closed position. The duct may have a semi-circumferential slot in its upper half through which the leading edge of the gate plate projects. The leading edge may be semi-circular in order to conform to the circumferential wall of the duct. 
     The gate plate may be substantially M-shaped with the upright outer members sliding in the gap between the parallel edges of the gate guides. 
     The inlet may have a ring flange for joining it to the ring flange of a pipe, which supplies the channel. 
     Utilizing such an apparatus, channel overflow may be prevented with consequent crop saving. 
     Utilizing such an apparatus, although the valve may not be watertight, leakage level is acceptable. 
     Utilizing such an apparatus, the valve requires minimal maintenance and has reduced vulnerability to blockage. 
     A second apparatus aspect of the disclosure provides a stop valve for a tank comprising a duct with an inlet and an outlet, a rise and fall gate between the inlet and outlet, a float arm supported by the duct operable to open and close the gate in response to rise and fall movement of the float. 
     The duct may be T-shaped with the two outlets lying at 90 degrees to the inlet providing an axis parallel to the gate, whereby the float arm is pivotable about the axis, the gate being at one end of the arm and a float at the opposite end. 
     The T-shaped body has a cylindrical outlet portion with pairs of circumferential slots lying mutually opposite, and a coaxial sleeve inside the outlet portion, which is rotatable, in order to support a pair of parallel float arms that extend through the sleeve and the circumferential slots in order to connect the gate to a pair of floats attached to the float arms. 
     The circumferential gap between the valve sleeve and the valve body may be bridged by self-lubricating strip bearings. 
     The gate may have static guides that are wider than the inlet portion of the valve body and a flat gate that slides in the guides between an open position clear of the inlet portion and a closed position in which the gate lies in register with the inlet portion, thereby preventing flow. 
     The float arms may be rods fixed to the sleeve but free to rotate in the circumferential slots in order to cause the gate to execute linear motion moving from rise to fall and back. Each float arm may be connected to the gate by a link that accommodates the difference in linear and arcuate motion. 
     Thus, when the floats ascend, the arms rotate to an inclined diametrical position in which the gate is drawn downward to its closed position. As the floats descend, the arms rotate in the counter direction to a second inclined position in which the gate is elevated to its open position. 
     When the float arms lie horizontally, the gate lies in an intermediate position in which some flow restriction is imposed. 
     The leading edge of the sliding gate may be arrowhead shaped or convex. 
     The inlet portion of the valve body may have a ring flange for bolting the end of a branch pipe forming part of the distribution network. 
     A further apparatus aspect of the disclosure provides a combined flow regulator and stop valve comprising a T-shaped valve body with an inlet axis and an outlet axis lying transversely to the inlet axis, a gate disposed across the inlet parallel to the outlet axis, a cylindrical portion of the valve body disposed about the outlet axis, a cylindrical valve member retained in the cylindrical portion, having a flow aperture connecting the inlet to the outlet or outlets, pairs of circumferential slots in the cylindrical portion of the valve body and a pair of arms that pass diametrically through both the pairs of slots and the valve body, one end of each arm being attached to the gate, the opposite end being attached to a float, whereby ascent of the floats both rotates the valve member to reduce flow and causes the gate to move from an open position toward a closed position and descent of the floats also rotates the valve member to increase flow and causes the gate to move toward the open position. 
     Preferably, the inlet axis is disposed at 90 degrees to the outlet axis. 
     One apparatus aspect of the disclosure provides a flow-regulating valve for a liquid container comprising a valve body with an inlet and at least one outlet, a rotary valve member in the body, wherein the valve body has means to rotate the valve member in response to the water level outside the valve body in the container, thereby regulating flow rate. 
     The valve body may be cylindrical. The valve member may likewise be cylindrical. 
     The valve member rotates in response to the rise and fall of one or more floats. 
     The valve body is cylindrical having two ends, an inlet between the ends and the valve body may have a passage connecting the inlet with one or both ends, the rotation of the valve member being dependent on the rise and fall of the water level in the container. 
     The valve member may have a float arm projecting through the valve body and a float connectable to the float arm. 
     Preferably, the valve member is rotated by a pair of arms. 
     The body may have a slot for each arm extending 22-45 degrees around the circumference of the body. The valve member may rotate coaxially in the body and have a cutout shaped to change the flow as rotation occurs. 
     The valve may have bearings attached to the body or the member, which facilitate rotation. The bearings may be spaced at 120 degrees. The bearings may be circumferential strips of material with a low coefficient of friction. 
     The float arms may extend through the wall of the valve member being removably fixed to the member at one end. The opposite end may carry a counterweight biasing the member to the fully open position. The float arms retain the valve member inside the valve body, allowing its rotation but preventing axial movement. 
     The free ends of the float arms each have a chain shackle that allows the floats to be attached by chains. 
     The valve body may be made of plastic but will more usually be made of stainless steel. The diameter of the valve body may be 200 mm to 1800 mm. The wall thickness of the valve member may be 2 mm to 20 mm. 
     Another apparatus aspect provides a water distribution system comprising a bulk water container with a water inlet and one or more outlets for distributing water to land, a water inlet for receiving water from a pipe network, and a flow regulator admitting water to the container, wherein the regulator has a rotating flow restrictor that is float activated. 
     Utilizing such an apparatus, fluctuating network pressures are coped with while maintaining the required flow rate. 
     Utilizing such an apparatus, it is relatively easily inspectable for maintenance with few wearing parts requiring replacement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the disclosure is now described with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic section of farmland supplied by a network pipe through a distribution tank. 
         FIG. 2  is a perspective view of the regulator valve and floats. 
         FIG. 3  is a perspective view of the valve body. 
         FIG. 4  is a perspective view of the valve member. 
         FIG. 5  is a perspective view of a second embodiment with an added stop valve in the open position. 
         FIG. 5A  is the same as  FIG. 5  with the added stop valve in the closed position. 
         FIG. 6  is the same as  FIG. 5  with the stop valve in an intermediate position. 
         FIG. 7  is a perspective view. 
         FIG. 8  is a plan view of  FIG. 7 . 
         FIG. 9  is a perspective view when in the gate closed position. 
         FIG. 10  is a front view of the gate plate. 
         FIG. 11  is a cross-sectional diagram of a channel in which the device is deployed. 
         FIG. 12  is a perspective of the valve in  FIG. 5  with a gate collar. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , network pipe  2  is 900 mm in diameter and branch pipe  4  brings water to the 1200-mm diameter tank  6  through a butterfly valve  8  past a flow meter  10 . 
     Referring now to  FIGS. 2 and 3 , the regulator valve  12  is bolted to the end of the branch pipe  4  and discharges into the tank. The valve body stem  14  is a T-shaped pipe of 320 mm diameter, the body being 510 mm long and the valve body stem  14  terminating in a connector ring  16  with bolt holes  18  for connection to the end of the branch pipe  4 . Both the body  20  and the valve member  22  ( FIG. 4 ) are made of stainless steel. Water enters the regulator valve  12  via the valve body stem  14  and discharges through the open ends of the body  20 . The flow through the valve is controlled by the valve member  22 , which is a sleeve of the same length as the valve body, namely 510 mm. 
     Referring now to  FIG. 2 , the circumferential gap  24  is bridged by a trio of bearing strips  26  made of a slippery polymer and attached to the edge of the valve member by stainless steel fasteners (not shown). The strips are spaced at 120 degrees, enabling the member to rotate in the body with minimum friction. 
     Referring now to  FIG. 4 , the crown of the valve member  22  has a cutout  28  with a straight edge  30  and tapered edges  32  extending over about 90 degrees of the circumference of the member. The cutout  28  lies in register with the connector ring  16 . 
     The ends of the valve body  20  have pairs of slots  34 ,  36 , 11 mm wide (see  FIGS. 2, 3 and 5 ) extending 90 degrees around the quadrants facing the water below the valve body  20 . The slots  34 ,  36  define the path of a pair of 10-mm diameter stainless steel rods  38  that are a slide fit in the slots. The rods pass through bores  39  near the edge of the valve member and are bent at one end into a foot  40  ( FIG. 2 ) that is secured to the valve member by a split pin  42  ( FIG. 2 ). The foot  40  is housed in the thickness of the valve member  22  and the end of the pin  42  rides in the slot in the valve body. 
     Referring to  FIG. 2 , the opposite end of each rod has a bore that receives a shackle  44  for connecting the arm to float chain  46 . The chain is about 600 mm long and runs through the shackle and is attached to itself. The chains each capture a spherical molded plastic float  48 . The floats are balanced by pivoted counterweights  50 . The chain  46  adjusts to suit the water level required. This allows for almost any water level required to be accommodated without affecting the functionality of the valve. 
     In use, the pipework is installed and the valve is suspended above or within the operational range of water levels in the tank. The floats lie on the surface of the water and the counterweights rotate the valve body to the open position. As the land dries and the tank empties the floats lie on the tank floor. 
     When the operator opens the butterfly valve  8 , the meter begins to measure flow. The operator selects a suitable flow rate and the container allows inflow to feed the outflow pipes. 
     The tank level rises and equilibrium is established. If the incoming flow fluctuates, the valve restores the equilibrium by rotating. 
     It is not the purpose of the valve to halt flow. That is the task of the butterfly valve  8 . The valve ensures a constant head of water in the tank, whereby the irrigation proceeds in an orderly manner despite the fluctuations in the network. A head of 3 m to 5 m is usual in such networks, but this may spike to 10 m. 
     In a second embodiment,  FIGS. 5, 5A and 6  show valve body stem  14  is divided by a pair of square frame plates  52 ,  54 . Plate  52  is attached to the valve body  20 . Plate  54  is attached to the part of the stem with the connector ring  16 . The gap  62  between the parallel plates  52 ,  54  is bridged by pairs of gate guides  56 ,  58  attached to the upright side edges of frame plates  52 ,  54 . For both guides  56 ,  58 , the gate gap  62  extends the full length of the guide. 
     The gate itself is a modified M-shape made of steel sheet that is wider than the gate guides spacing and has two legs  64 ,  66  joined by an upper part  68  with a convex leading edge  70 . The legs have slots  72 ,  74  for reception of the pivoting connections  76 ,  78  ( FIG. 7 ) of float arms  38 . 
     In the open position shown in  FIG. 5 , the gate rises clear of the frame plates  52 ,  54 . In the closed position shown in  FIG. 9 , the leading edge  70  meets the circular perimeter of valve body stem portion  14  and the part  68  registers with the frame plates  52 ,  54 . 
     The float arms  38  are fixed to the sleeve  22  to ensure that the floats exert the same uplift force as in the previous embodiment. The pivoting connections each have a central self-lubricating bush through which the float arm is free to slide in order to accommodate the linear rise and fall of the gate. The projection of the rods through the legs  64 ,  66  is seen in  FIGS. 6, 7 and 9 . The counterweights&#39; mass is increased to adjust for the weight of the gate. 
     The float arms lie in an intermediate position when the tank is both filling with network inflow and emptying into the irrigation pipes. The cutout  28  of sleeve  22  registers with the valve body stem  14  and, from this position, the floats quickly react to any increase in head. If the head persists, the floats press the gate into the closed position. As the tank drains, the floats descend. If the head has diminished, the gate may not reopen. If the tank drains further, the gate may reopen. 
     In a third embodiment,  FIG. 11  shows an irrigation channel 3 m to 4 m wide and 2 m deep that is fed by a steel pipe that brings pumped water from a bulk source such as a dam. The shape of the channel is as shown in  FIG. 11  and the pipe is submerged so that the floats can exert flow control on the incoming water. 
     Referring now to  FIGS. 8 and 9 , the float-activated stop valve is connected to the external delivery conduit by ring flange  16 . Stem  14  is 300 mm in diameter and 700 mm long. The rise and fall gate straddles an incision (not shown) in the upper half of valve body stem  14 . The steel gate guides  56 ,  58  are separated by gap  62  and welded to the outer surface of the valve body stem  14 . Gate gap  62  extends the full length of the guides. 
     The gate itself (see  FIG. 10 ) is a modified M-shape, made of stainless steel that is wider than the width of the gate guides and has two legs  64 ,  66  joined by an upper part  68  with a convex leading edge  70 . The legs have slots  72 ,  74  for the reception of the pivoting connections  76 ,  78  of float arms or rods  38 . The guides  56 ,  58  have pairs of slots  77  adjacent gate gap  62  in order to support the screws of pairs of vertical self-lubricating polymer strips  79 . The slots  77  allow accurate adjustment of gap  62  size leading to smooth motion of the gate. Upper part  68  supports a semi-circular collar  80 , 25 mm wide, which overlies the incision when the gate is closed. In the closed position, the convex leading edge  70  contacts the circular wall of the stem. 
     The 22.5 degree rotary motion of the float arms  38  is made possible by the horizontal transverse pivots  82  welded to the outside wall of the valve body stem  14 . The counterweights and floats work in the same way as described in related Australian Patent Application Serial No. 2013902805. The water flow passes between the parallel float arms. 
     Referring now to  FIG. 12 , the leading edge  70  closes the duct by descending to contact the lower cylindrical wall of the valve body stem  14 . The semi-circular collar  80  then rests on the upper part of the same wall. 
     It is to be understood that the word “comprising” as used throughout the specification is to be interpreted in its inclusive form, i.e., use of the word “comprising” does not exclude the addition of other elements. 
     It is to be understood that various modifications of and/or additions to the disclosure can be made without departing from the basic nature hereof. These modifications and/or additions are, therefore, considered to fall within the scope of the invention.

Summary:
Irrigation valves for channels and for irrigation tanks are of three types. All are activated by a pair of tilting float arms to which a pair of floats are attached. One type is a T-shaped duct with a cylindrical valve disposed at 90 degrees to the part that is connected to the incoming flow. The floats rotate the valve. The second type has the same construction as the first type, thereby giving flow control but additionally has a rise and fall gate in the duct part that is connected to the incoming flow. The gate acts as a stop valve. The third type has a cylindrical duct connectable to the incoming flow but no valve and provides both flow control and stop valve facilities through a rise and fall gate actuated by the tilting of the float arms.