Abstract:
A water treatment and/or irrigation system which includes a source of water under pressure, such as a pump, an optional filter that receives water from the pump and emits filtered water under pressure, a system of irrigation lines that receives water under pressure for distribution to a field, and a flushing system for periodically cleaning the irrigation lines and/or the filter. The flushing system has a pressure vessel that receives the water under pressure and periodically builds its pressure to a level in excess of the normal level of the pressure delivered to the field, followed by discharging the built-up pressure as sharp pulses separated by one or more short time intervals directed toward the irrigation lines and/or the filter to effect cleaning thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to irrigation systems, and more particularly, to a system and method for flushing irrigation systems, including drip irrigation lines, drip irrigation emitters, and filters used in irrigation systems. 
       BACKGROUND 
       [0002]    Irrigation systems need to be periodically flushed to remove foreign materials which may have accumulated in the tubes. In particular, drip irrigation systems need to be flushed particularly well, due to the small size of the flow paths in the emitters; and, drip irrigation systems used for effluent disposal and reuse need the maximum degree of flushing. 
         [0003]    Anti-bacterial linings have been used in irrigation systems, including drip irrigation systems and in waste water disposal systems. These anti-bacterial linings can inhibit the growth of slime which occurs inside supply lines or drainage lines, especially in waste water disposal systems. Irrigation lines having such anti-bacterial linings are disclosed in U.S. Pat. No. 5,332,160 to Ruskin. 
         [0004]    Lower cost products not containing the anti-bacterial lining are more commonly used for irrigation and waste water disposal and reuse. Because the build up of slime is inevitable in irrigation and waste water systems, the tubes need to be periodically cleaned to remove slime or other organic matter that accumulates. A common practice is to operate a flushing cycle that cleans or at least partially cleans the tubes, the drip irrigation emitters, filters and the like. U.S. Pat. No. 5,200,065 to Sinclair et al. discloses a turbulent flow system for flushing a dripper field, for example. According to The American Society of Agricultural and Biological Engineers flush velocity standards, a minimum flow velocity of 0.3 m/s (1 ft/s) is needed for flushing of lateral lines. 
         [0005]    Generally speaking, there are three regimes of flow:
       (1) Laminar flow, Reynolds no. less than 2000   (2) Unstable flow, Reynolds no. between 2000 and 3000   (3) Turbulent flow, Reynolds no. greater than 3000.
 
Flushing a pipeline with a set or recommended velocity, such as 2 ft/sec, will not necessarily produce a turbulent or unstable flow. Pipe diameter and the resulting area of the flow path also are factors that determine the desired flushing necessary for cleaning the pipe wall.
       
 
         [0009]    As to the desired “scouring” effect for flushing pipelines, in some instances turbulent flow, depending on the Reynolds number, can produce a flow pattern at the wall interface which does not produce a scouring effect. According to the National Onsite Wastewater Recycling Association&#39;s Recommended Guidance for Design of Wastewater Drip Dispersal Systems, “scouring” is defined as the “process to clear a conduit of particulates by hydraulic flushing at a sufficient velocity to lift and carry particulates downstream.” 
         [0010]    Present flushing technology consists of opening the ends of the dripper laterals and passing the water (or effluent) through the tubes. Sometimes the velocity of flow is designed to exceed a minimum standard, such as two feet per second, in order to achieve turbulent flow, and thereby to scour growth off the walls of the tube. In most cases, this flushing flow, turbulent or laminar, does not remove any foreign material from inside the emitter. 
         [0011]    To offset the lack of an anti-bacterial lining, by flushing driplines with a high velocity—for example, two ft/sec as is recommended by some manufacturers—higher pump pressures are required. This requires substantial field and flushing pressure, leading to use of expensive filter/pump systems, sometimes including two filters and often two separate pumps. Furthermore, due to the frictional loss in the tubes at high velocities, it is necessary to use shorter laterals, resulting in higher costs for more supply and flush piping and installation labor. 
         [0012]    All drip irrigation systems require filtration. Periodically, filters must be cleaned, either manually or automatically. 
       SUMMARY OF THE INVENTION 
       [0013]    This invention comprises an improved system and method of flushing irrigation system pipelines. The invention is particularly suitable for flushing drip irrigation pipelines. The invention in many cases will provide improved flushing of the emitters. The invention also can be used as a filter flushing device. 
         [0014]    Briefly, one embodiment of the invention comprises a water treatment and/or irrigation system which includes a source of water under pressure such as a pump, an optional filter that receives water from the pump or other source of water under pressure and emits filtered water under pressure, and a system of irrigation lines that receives the water under pressure for distribution to a field. The irrigation lines comprise conventional irrigation pipelines and/or drip irrigation pipelines containing emitters. A flushing system periodically cleans the irrigation lines, the emitters and/or optionally the filter. The flushing system includes a pressure vessel or reservoir that receives the filtered water under pressure. The pressure vessel is adapted to periodically build its pressure to a level substantially in excess of a normal level of pressure in the water delivered to the field. This is followed by discharging the water under its built-up pressure as one or more sharp pulses directed toward the irrigation lines, the emitters and/or optionally the filter to effect cleaning of the conventional irrigation pipelines, the drip irrigation pipelines, the drip irrigation emitters, and/or optionally the filter. 
         [0015]    The pressure build up is released as a high pressure shock substantially higher than normal operating pressure and at a flow rate substantially higher than turbulent flow that has been used in the past for cleaning drip irrigation lines or emitters, for example. This high pressure shock or pressure pulse, which can be delivered as a single shock impulse, or as a series of separate pulses separated by short time intervals, has been shown to produce greatly improved cleaning of irrigation lines, drip irrigation lines, drip emitters and filters. 
         [0016]    An improvement provided by the present invention is a more effective flushing of driplines and drip emitters compared with prior art systems using turbulent flow for flushing. Flushing of filters also is improved, and system operations can be carried out with smaller and less expensive filter and pump systems. 
         [0017]    These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a schematic diagram showing an example of a water treatment system or irrigation system with which the flushing device of this invention may be used. 
           [0019]      FIG. 2  is a graph of net pump discharge versus total dynamic head illustrating various conditions of a pump of the type which can be used in the water treatment or irrigation system of this invention. 
           [0020]      FIG. 3  is a schematic view illustrating a mechanically driven piston and cylinder illustrating an alternative form of a pressure vessel according to principles of this invention. 
           [0021]      FIG. 4  is a schematic diagram showing a spring-loaded piston which is an alternate pressure vessel that may be used in the flushing system of this invention. 
           [0022]      FIGS. 5 and 6  are schematic cross-sectional diagrams illustrating a commonly used pressure-compensating emitter which illustrates a type of drip irrigation device that can be cleaned by the flushing system of this invention. 
           [0023]      FIG. 7  is an exploded assembly view illustrating components of a screen filter which can be cleaned by the flushing device of this invention. 
           [0024]      FIG. 8  is a schematic diagram showing an alternative water treatment system or irrigation system using the flushing device of this invention. 
           [0025]      FIG. 9A  is a schematic diagram illustrating an alternative method for operating the flushing system of this invention;  FIG. 9B  is a schematic diagram illustrating a variation of the flushing system and operation method of  FIG. 9A . 
           [0026]      FIG. 10  is a schematic diagram showing an irrigation system using the flushing device of this invention and also illustrating locations of pressure gauges used in a system for producing test data showing comparative effects of the flushing system. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    It is common practice in the irrigation industry to flush pipes by opening the ends of the lines and allowing the water pressure to flush organic matter or other debris out of the system. The recommended flush velocity will vary over a wide range according to (1) the material to be flushed out, (2) the diameter of the tube, and (3) the qualities of the inside lining of the tubes. In some instances turbulent flow is recommended. High flush velocities may require either larger or more pumps than may be required for operating the system. This particularly applies for drip irrigation, because the flows through the drippers are relatively low, resulting in small operating flows and small pumps. 
         [0028]    An objective of the present invention is to apply one or more short sharp pulses of flow followed by or interrupted by short periods of no flow. These pulses can be applied to produce a shock or supercharged flow that flushes out the debris in the system or cleans any part of the system which is designed to be cleaned by a flow of water. 
         [0029]      FIG. 1  is a schematic diagram illustrating a flushing system and method of this invention as applied to a system for treating and disposing of waste water. The  FIG. 1  system is simply an example showing principles of this invention in a particular application. The invention also can be used for flushing irrigation systems generally, and in some cases, for flushing drip irrigation emitters. The invention also can be used as a filter flushing system. The invention also is described with respect to treatment and disposal of effluent from a treatment plant, however, the terms “effluent,” “waste water,” and “water” are used interchangeably herein to describe principles of the invention. 
         [0030]    Referring to  FIG. 1 , a waste water treatment and disposal system includes a supply  10  of waste water to be treated, typically effluent from a treatment tank and a downstream dosing tank that feeds effluent to the waste water treatment system on demand. The waste water supply to the treatment system can be treated water from a septic tank or secondary or tertiary treated waste water effluent, for example. The effluent is supplied to a pump  12  which forces the effluent through a filter  14 . Use of the pump  12  is one example as applied to the illustrated system. Alternatively, the water or other effluent can be supplied to the system by an external source of water under a supply pressure. The filter has a filter flush valve  16  that is normally closed during system operation, but the valve is opened when flushing the filter. The filter  14  is useful in the illustrated system, but the filter is an optional component. Other systems to which the invention may be applied, such as sprinkler systems, may not include a filter. The effluent passes from the filter through a flow line  18  leading to a dripper field  20 . The effluent passing to the dripper field fills a pressure vessel  22 . The pressure vessel can be any of several types of devices that contain filtered water under a normal operating pressure but are adapted to increase the pressure of the contained water on demand. The pressure vessel of  FIG. 1  can be a bladder-type vessel in which the bladder is compressed to its operating pressure during normal operations in which the filtered effluent is sent to the dripper field. In one embodiment, the pressure vessel comprises a WELL-X-TROL 8.6 gallon hydro-pneumatic tank. This pressure vessel was used in experimental tests as described below. 
         [0031]    With the pressure vessel  22  filled and the system operating at normal system pressure or pump pressure, the effluent passes through the supply line  18  to the dripper field. The line to the dripper field leading away from the pressure vessel includes a field supply valve  26 . This valve is normally open during normal operation of the waste water treatment and disposal system. 
         [0032]    The pressure vessel is connected to the flow line  18  through a check valve  23  and a control valve  24  which is normally closed during normal operation of the system and the pressure vessel will always pressurize through the check valve. In a system in which normal pump operating pressure is 30 psi, for example, pressure in the hydro-pneumatic tank is 30 psi. Then when pressurizing beyond operating pressure, the field supply valve  26  will close and pressure builds up in the pressure vessel  22  as the pump goes to or near a static flow condition. 
         [0033]    In some instances, the control valve  24  is not needed. If the pressure in pressure vessel  22  is allowed to build to say 60 psi, and then immediately letting the surge flow (as described below) with valves  24  and  26  both open, then valve  24  is redundant to valve  26 . However, if one wants to increase the pressure while performing other operations, such as turning off the pump in order to give the drippers (described below) an extra long draining time, without keeping the pump operating in a static condition for a longer time than necessary to bring vessel  22  to 60 psi, for example, then valve  24  is kept closed. Keeping valve  26  closed with valve  24  open would result in the surge going back through filter  14 , pump  12  and into the supply source  10 . When using the surge to clean the filter  14 , as described below, a check valve (not shown) between the pump  12  and filter  14  can be useful to prevent the surge going back through the pump. The pump can be kept running during flushing of the filter, but there are configurations of filters where this may not be desirable. 
         [0034]    The dripper field includes a supply manifold  28  having separate lateral rows of parallel drip irrigation lines  30  overlying the dripper field. Each of the dripper lines has spaced apart drip irrigation emitters  32  through which the treated effluent flows to the ground. The ends of the drip irrigation lines tie into a common return manifold and discharge line  34  leading to a field flush valve  36 . This valve is normally closed during normal operation of the waste water treatment and disposal system. The field flush valve  36  can be opened for flushing the dripper field or at select time intervals for returning effluent back to an initial treatment tank. 
         [0035]    The drip lines shown in  FIG. 1  and the related manifolds and drippers are similar to a landscape system, for example, to which the flushing system also can be applied. 
         [0036]    During normal operation, the pump  12  supplies water to the field. The field supply valve  26  is open, the control valve  24  for the pressure vessel is open, and the field flush valve  36  is closed. The bladder contained in the pressure vessel  22  is compressed to the operating pressure. 
         [0037]    During flushing, the field supply valve  26  is initially closed and the field flush valve  36  is opened. (The pressure vessel control valve  24  remains open.) The pump builds pressure in the pressure vessel  22  to a pressure substantially in excess of normal pump pressure. At a preset pressure a pressure monitor (not shown) on the pressure vessel sends a control signal to open the field supply valve  26 . A surge of water in the form of a pressure pulse is sent through the irrigation lines  30  in the field from the pressure vessel  22 . The pressure in the pressure vessel is raised to a pressure level that can produce a sudden pressure pulse that produces a supercharged shock to the driplines  30  for cleaning the lines. The pressure in the pressure vessel drops, and at a preset low pressure level, the pressure monitor sends a control signal to close the field supply valve  36 . The pressure in the pressure vessel then builds again, and a second pressure pulse can be generated. The cycle is repeated as often as may be required. At the end of the flushing cycle or cycles, the field flush valve  36  is closed and the field supply valve  26  is opened and normal operation is resumed. 
         [0038]    A high pressure surge or impulse is obtained due to the nature of almost all commonly used pump curves. Referring to  FIG. 2 , normal operating conditions may be at point A, i.e., 20 GPM at 100 feet dynamic head. When the field supply valve is closed then the flow to the field drops to zero and the pressure in the pressure vessel can build to point B, at say 170 feet dynamic head. 
         [0039]    The pressure pulse generated by the flushing system of this invention is produced by allowing pressure to build up in the pressure vessel to a level well in excess of normal system operating pressure or pump operating pressure. In the embodiment in which normal system or pump operating pressure is 30 psi, the pressure is allowed to expand to more than about 50 psi, and more preferably about 60 psi. Recognizing that different system operating pressures or pump pressures and pressure reservoirs can be used, the flushing dynamic is generally effective by building pressure to at least about 50% more than normal system or pump operating pressure, followed by opening the field supply valve so as to immediately drop the reservoir pressure. 
         [0040]    To clean the dripline emitters, as opposed to the driplines themselves, the flushing system is operated to drop the pressure at the emitter to zero and then reapply the pressure, thereby first allowing the rubber diaphragm in the emitter to move back from the outlet, followed by driving the diaphragm forward to expel any debris that may have lodged in the emitter. Both the field supply valve and the field flush valve are closed. The water in the field drains through the drippers and pressure drops to zero, at the same time that pressure in the pressure vessel expands to say 60 psi. Then the field supply valve is opened, causing a pressure surge in the driplines, ejecting foreign material from the drippers; This procedure can be repeated several times until normal field flow rates are restored. 
         [0041]    Many hydrodynamic pressure devices can generate a pressure surge as described above. For example, as is shown in  FIG. 3 , a mechanically driven piston  40 , which draws water into the cylinder  42  and expels it a high pressure, can be used. Alternatively, a spring loaded piston  48  in a cylinder  50 , as illustrated in  FIG. 4 , can be used. The cylinder is pushed back by the water pressure and provides the surge by means of the spring pressure. The invention is not limited to the method used to provide the surges of high pressure flow. 
         [0042]    In the case of drip irrigation, surges of flush water may be an efficient way to clean some drip irrigation emitters. Drip emitters are manufactured in many different designs, and some can be cleaned effectively by the flushing system of this invention. A commonly used type of pressure compensating emitter is shown in  FIGS. 5 and 6  This emitter is a type of pressure compensating emitter made by The Toro Company, El Cajon, Calif. and available from Geoflow, Inc., Corte Madera, Calif. This emitter contains a rubber diaphragm  52  which is deflected against the outlet  54  of the emitter by the internal water pressure. When the pressure is removed, the diaphragm springs back and leaves the outlet open. Then when the water pressure is again increased, the first short burst of water, before the diaphragm closes, flushes through the outlet, thereby cleaning out any debris in the dripper. A study by the Center of Irrigation Technology, has demonstrated that this type of dripper is efficiently cleaned by such a cycle of pressure off/pressure on. Cleaning is particularly improved using the pressure impulse system of this invention. Because these drippers are pressure compensating, the flow through the dripper is nearly constant at all practical pressures, and high velocity flushing of the drip irrigation supply line, such as by turbulent flow, will leave the diaphragm in its operating position, and will have no cleaning effect upon the dripper. 
         [0043]    Another commonly used design of dripper (not shown) is known as a turbulent flow emitter. Such an emitter is also available from Geoflow, Inc. The flow in the emitter is proportional to the pressure. The alternating surges of pressure may dislodge some materials in the flow path. The cleaning of this type of emitter by the flushing system of this invention may be effective, but is not as effective as the pressure compensating example. If the main purpose of the surge is to clean the emitters, then the field flush valve can remain closed through the entire cycle and all the pressure and flow from the surge will be available for cleaning the emitters. Best results may be obtained by first cleaning the tubes with the field flush valve open, and then completing the cleaning of the emitters with the field flush valve closed. 
         [0044]    The system shown in  FIG. 1  can be used for flushing the filter. An example of the filter is a normally forward flushing screen filter as shown in  FIG. 7 . The filter includes an upper housing  56 , an O-ring  58 , a debris basin  60 , a screen  62  and a spin plate  64 . By opening the filter flush valve and closing the field supply valve, the high pressure cleaning pulses can be applied to backflush through the screen of the filter. If the pump is left running flushing is both forward and backflushing simultaneously Under certain hydraulic conditions the field supply valve can stay open and the larger part of the surge will still pass backwards through the filter. There are many types of filters used in the irrigation and waste water treatment industries, and this technique will useful for some, but not for all. Another example of a filter which may be used with the invention is a disk filter such as the Arkal family of disk filters. 
         [0045]      FIG. 8  is an alternative embodiment of the invention in which the flushing system is adapted for cleaning the manifolds connected to the dripline laterals in the field. This embodiment, which is similar to the  FIG. 1  embodiment, includes the effluent supply  70 , the pump  72 , and a filter  74  for supplying filtered effluent through a supply line  76  to the field  78 . A pressure vessel  80 , which can be similar to the bladder type pressure vessel  22  described previously, is connected to the supply line through the check valve  82  and the control valve  84 . The system of  FIG. 8  also includes the filter flush valve  86 , the field supply valve  88 , and the field flush valve  90 . Filtered effluent in the supply line  76  downstream from the pressure vessel  80  is sent to the driplines  92  in the field, through a supply manifold  94  having a flush valve  96  upstream from the driplines  92 . The effluent passing from the driplines passes through a flushing manifold  98  and the field flush valve  90 . 
         [0046]    The system shown in  FIG. 8  is adapted to clean the manifolds with or without the high pressure shock described previously. During normal operation in which the effluent is sent to the driplines, the pump stays running and the field supply valve  88  is open, the flush valve  96  is open, and the field flush valve  90  also is closed. This will allow the drip lines  92  to be filled from both ends, allowing a very fast and efficient fill time. For cleaning the manifolds without applying high pressure shock, the field supply valve  88  is open, and the flushing valves  96  and  98  are opened. The pump also can be operated at higher than normal pressure to produce a turbulent flow in the manifolds. This can produce a scouring effect in the manifolds. Alternatively, the high pressure shock can be applied to the manifolds by closing the field supply valve  88  to build pressure in the pressure vessel, while the valves  96  and  90  are opened. Opening the field supplyvalve  88  produces the high pressure shock for cleaning the manifolds. 
         [0047]    There are two distinct flush cycles:
       (1) Valve  88  will close for the full pressurization. Then valves  84 ,  88  and  90  will open simultaneously with valve  96  still open from the previous operating cycle. This can be referred to as the flush manifold flush cycle.   (2) Valve  88  will close to re-pressurize the vessel, and then with valves  84 ,  88  and  90  open and valve  96  closed, the drip lateral flush will occur.       
 
         [0050]      FIG. 9A  illustrates an alternative form of the invention having an alternating 4-valve system  100  for controlling the direction of flushing flow through the driplines and the manifolds. This embodiment is similar to those described previously in which filtered effluent passes through the supply line past the pressure vessel or other reservoir that builds up pressure. This embodiment includes the usual arrangement of the supply manifold  102 , the return manifold  104 , and the driplines  106  with their drip irrigation emitters  108 . The four-alternating valve system includes a first pair of valves  110  and a second pair of valves  112  which in one cycle are in the normally open or normally closed positions as shown in  FIG. 9A . The field flush valve  114  also is shown in its normal position downstream from the dripper field and the return manifold  104 . This system can be used to alternate the flush and supply manifold functions: With the valves set in their normally open and normally closed positions as shown in  FIG. 9A , flushing takes place from left to right in  FIG. 9A  in its normal manner. All four valves are then switched simultaneously to an alternative cycle in which flushing takes place from right to left with reference to  FIG. 9A . Because water is normally lost down the dripperline through the drippers, the velocity at the supply end is much more rapid than at the flushing end. Therefore, alternating the direction of the flushing ensures that the whole pipe is subjected to maximum flush velocity. This flushing cycling can be combined with the hydrodynamic tank or other high pressure impulse system as described previously so as to provide a vigorous cleaning action. Alternatively, the four alternating valves can be replaced by two 3-way valves. 
         [0051]      FIG. 9B  combines the systems and methods of operation of  FIGS. 8 and 9A . The backward and forward flushing as illustrated in  FIG. 9A  could in some circumstances result in an excessive build-up of material in the manifolds, which then can be flushed according to the method of  FIG. 8   
       EXAMPLE 
       [0052]    An irrigation and pressure flushing system as shown in  FIG. 10  was constructed and operated to test the pressure flushing system of this invention. Comparative tests were conducted to show the results of operating the irrigation and flushing system at normal operating conditions using flushing at a rate of two feet per second to produce turbulent flow through the driplines, compared with using the pressure shock system of this invention to apply high pressure pulses greatly in excess of normal pump operating pressure. The test system was set up with four pressure gauges to measure pressure at different locations in the system. The illustrated test system included a pressure gauge  116  for measuring pump pressure, a pressure gauge  118  for measuring pressure in the pressure tank  22 , a pressure gauge  120  for measuring the pressure of filtered effluent passing through the field supply manifold in the driplines, and a pressure gauge  122  in the field flush manifold to measure pressure in the return line downstream from the driplines. 
         [0053]    The pump was normally run at 30 psi. For the high pressure shock test, the pump with a normal operating pressure of 30 psi generated 60 psi in the pressure chamber, followed by opening the field supply valve. Test results are shown in the attached Appendix. These tests involved primarily a set of field flush tests in which the filter flush valve remained closed and the field supply and field flush valves were opened. Filter flush tests also were conducted with the field supply valve closed and the field supply valve open, as indicated in the test results. As for the field flush tests, comparative tests were conducted to measure flow rate in the driplines for high pressure shock tests compared to normal pump operating conditions. For each set of comparative tests as shown in the test results, the top row indicates the flushing flow rate in feet per second compared with the second row which shows the flushing flow rate under normal pump operating conditions. These comparative tests show that the high pressure in excess of normal operating pressure provided by the present invention in each case produced substantially greater field flushing flow rates than flushing conducted under normal operating conditions, absent the high pressure flushing pulses.