Abstract:
A variable-rate, digitally controlled fluid metering device having an electronically controlled 3-way valve, a fluid reservoir, a float valve, a check valve and a pressure relief valve that accurately delivers low flow volumes. The flow rate of the device is the product of reservoir volume and pulse rate when the cycle is long enough to fill and empty the reservoir and is a linear combination of cycle time when the cycle is short enough that the reservoir does not fill or empty completely. This device allows the use of large orifice emitters for delivering low flow rates of fluids, which allows the use of lower quality fluids and/or reduces filtration steps and clogging of emitters.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a variable-rate, digitally-controlled fluid metering device for use in applications such as, for example, mixing of fluids, injecting variable volumes of fluid into fluid streams, spraying chemicals in process lines, cooling of rooftops, livestock, poultry etc. The invention also relates to the use of the fluid metering device in spray irrigation systems. 
     2. Description of the Related Art 
     Conventional methods vary emitter size or pressure to regulate flow rates of fluids, which can cause problems because of limited range of pressures and flows, changed pattern radius, and changed distribution uniformity within the pattern. For sprinkler systems, problems occur because of changed pattern radius and changed distribution uniformity within the pattern. For injection of fluid treatment agents, nozzles usually have relatively small passages for low volume flow rates, which are highly prone to plugging if small sized particulate matter is present in the injection fluids. Furthermore, in systems such as, for example, agricultural irrigation systems, it is desirable to discharge precise amounts of fluids regardless of pressure variations. Standard sprinklers in agricultural irrigation systems, use fixed-orifice designs, which have corresponding pressure-flow relationships. By design, the flow rate of a given sprinkler at a given pressure is fixed. In movable irrigation systems, application depths are altered in practice by altering the travel rate of the sprinkler over the ground. Constant-speed machines use time-proportional control, meaning they must stop periodically to reduce average travel velocity. Intermittent motion degrades the uniformity of application, and the uniformity is worse for smaller sprinkler pattern radii. Alignment control of multi-span center pivot and linear-move machines superimposes another start/stop pattern on inner towers. Some standard sprinklers are used in a time-proportional, switched mode. Solenoid valves turn the supply on and off in a controllable sequence. The control variable is the length of time the water is on relative to the cycle time. The dynamics of the solenoid are a limiting factor and the uniformity of application may not be adequate. 
     U.S. Pat. No. 5,134,961 (Giles et al) discloses a device for controlling volumetric flow through pressure atomization sprays. Each nozzle is connected to a direct acting, in-line solenoid valve which is connected to a liquid supply at constant pressure. The valve is excited by square wave pulses of variable frequency and duty cycle to reciprocate between its fully open and closed positions and thereby control the flow rate over a range without changing the droplet size and spray pattern. 
     U.S. Pat. No. 4,867,192 (Terrell et al) discloses an apparatus for controlling irrigation water pH by blending a minute stream of sulfuric acid into a flowing water stream. The sulfuric acid pumps are variable displacement, positive displacement pumps which are electrically driven and controlled by a controller through electrical circuits. 
     U.S. Pat. No. 5,271,526 (Williams) discloses a programmable additive controller which controls the flow of fluid additives. A flowmeter is connected to a solenoid control valve for measuring flow of fluid. The controller opens and closes the valve and incorporates an input for required quantities of additive to be added each cycle. This system has a minimum injection per cycle of about 5 or fewer cc&#39;s per cycle. A comparator in the controller compares a required quantity with signal output indicating flow through the flowmeter. The difference between actual flow and target flow is continuously sent so that the target flow is continuously adjusted up or down when necessary to compensate for the previous difference. 
     While various devices have been developed for variable flow of fluids, there still remains a need in the art for a more effective and accurate device for delivering fluids at variable flow rates. The present invention provides a variable-flow rate, digitally-controlled fluid metering device that can use any type of emitter for delivering fluids at a wide range of flow rates by controlling the pulse rate for a given reservoir volume. The controllable range of flow rates can be expanded by replacing with different sized reservoirs. The present invention is different from prior art devices and solves some of the problems associated with the prior art devices. The present invention allows the use of large orifice emitters for delivering low volumes of fluids which allows the use of low quality fluids and/or reduces filtration steps and clogging of emitters. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a digitally-controlled device that allows variable flow rates of fluids with positive displacement. 
     A further object of the present invention is to provide a fluid metering device with a flow rate that is a linear combination of cycle time when cycle time is short enough that the reservoir of the device does not fill or empty completely. 
     Another object of the present invention is to provide a device where the instantaneous flow rate from zero to maximum is controlled by a limited duration pulse. 
     Another object of the present invention is to provide a fluid metering device where flow rate is proportional to the number of pulses. 
     Further objects and advantages of the invention will become apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of fluid metering device  10  showing electronic control signal source  11 , an electronically controlled 3-way valve  12 , source of a second pressurized fluid  13 , float check valve  14 , fluid reservoir  16 , floating ball  18 , means for retaining ball  20 , check valve  22 , fluid supply line  23 , pressure relief valve  24 , source of a first pressurized fluid  29  and outlet  26 . 
     FIG. 2 is an exploded view of one embodiment of device  10  showing vacuum breaker casing  28 , floating ball  18 , retaining screw  34 , pipe  32 , female adapter  30 , tee  36 , first inlet  37 , first threaded nipple  38 , second inlet  39 , outlet  41 , check valve  22 , reducing bushing  40 , second threaded nipple  38  and pressure relief valve  24 . 
     FIG. 3 shows a cut-away view of another embodiment of device  10  showing male N.P.T. connection  42 , female N.P.T. connections  44 , float check valve  14  with floating ball  18  and float ball restraint  20 ; reservoir  16 , check valve  22 , pressure relief valve  24  and outlet  26 . 
     FIG. 4 is a graph showing volume of fluid discharged by device  10 , shown in FIG. 2, with variable pressure. 
     FIG. 5 is a graph showing volume of fluid discharged by device  10 , shown in FIG. 2, with variable discharge time. 
     FIG. 6 is a graph showing volume of fluid discharged by device  10 , shown in FIG. 2, with variable cycle time. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a variable-rate, positive displacement, digitally-controlled fluid metering device that works by cycling between a charging state, during which a fixed volume fills with fluid, and a discharging state, during which the volume is forced through an emitter attached to device  10 , at the outlet end of valve  24 , by a pulsed higher-pressure inert fluid, such as a gas, like air for example. As used herein, the term emitter means anything that delivers a fluid, either gas or liquid, such as for example, sprinkler heads, injection nozzles, industrial spray nozzles, open orifices, etc. The volume of fluid storage is a design parameter that can be easily altered to provide small changes in aggregate flow rate, providing for a wider range of possible flow rates, and providing a range of flow rates for a constant pulse rate using different sized reservoirs. The primary variable is pulse rate, which can vary the instantaneous flow rate from zero to maximum. This is accomplished with a square waveform of given duration with adjustable frequency. 
     FIG. 1 shows a schematic of fluid metering device  10  according to the present invention, comprising an electronically controlled 3-way valve  12 , a float check valve  14 , floating ball  18 , a fluid reservoir  16 , a means  20  for restricting the travel of ball  18  within said reservoir  16 , a check valve  22 , a fluid supply line  23  and pressure relief valve  24 . 
     The inlet end of electronically controlled 3-way valve  12 , a solenoid valve for example, operatively connects to the outlet end of source  13  of a second pressurized fluid, such as a gas; nitrogen, air, etc., for example, or a liquid. By definition, source  13  includes for example, compressors, pumps, bottled gases, bottled liquids, etc. The outlet end of controlled 3-way valve  12  operatively connects to the inlet end of float valve  14  through pipe  19  (See FIG.  1 ). Valve  14  is operatively connected to the inlet end of reservoir  16 . Valve  14  is required to vent the second pressurized fluid during the charging cycle. The vented fluid can be optionally captured and recycled. Valve  12  is controlled by electronic control signal source  11 , which can be any means to create a discrete on-off signal, by way of example, a programmable logic controller (PLC), a PC with an analog/digital I/O board, a data logger, etc. Reservoir  16 , containing floating ball  18 , is operatively connected to the outlet end of valve  14  and the inlet end of pressure relief valve  24 . Reservoir  16  is any means suitable for containing a fluid, under pressure, to be emitted. It is cylindrical in shape and can be removable in order to have different sizes of reservoirs which have different volumes per pulse. It can be cast from any rigid inert material, such as for example metals including brass, bronze or stainless steel, etc.; plastics such as PVC, and composites. Material choice is dependent on the application of device  10 . The design and fabrication is well within the ordinary skill in the art. Floating ball  18  travels vertically within reservoir  16 . Ball  18  is made up of any chemically inert low density material that is capable of sealing valve  14 , floating in the first pressurized fluid which is being emitted by device  10  and sinking in the second pressurized fluid. Chemically inert low density material is defined as any material that does not chemically react with the fluids used in device  10 , such as for example, PVC. 
     Means  20  for retaining ball  18  is located below reservoir  16  just above the entry of the first pressurized fluid from fluid supply line  23 . Means  20  is anything that stops ball  18  but does not restrict fluid flow into or out of reservoir  16 . Means  20  can be, for example, a retaining screw, a pin, screening material, etc. Means  20  also may be molded into the body of reservoir  16  as depicted in FIG.  3 . Means  20  and valve  14  restrict the movement of ball  18  within reservoir  16 . 
     Reservoir  16  is operatively connected to source  29  of a first pressurized fluid at pressure P 1  through check valve  22  that is connected to fluid supply line  23  between reservoir  16  and source  29 . The first pressurized fluid is the controlled fluid, and has a density greater than that of ball  18 . Check valve  22  prevents back flow of reservoir fluids into fluid supply line  23 . Pressure relief valve  24  is operatively connected to reservoir  16  below the outlet end of reservoir  16 , usually through tee  36  between reservoir  16  and valve  24  (See FIG.  2 ). Valve  24  operatively connects reservoir  16  with a fluid emitter through outlet  26  of device  10 . 
     In one embodiment of the invention, depicted in FIG. 2, vacuum breaker casing (including valve seat)  28  functions as float valve  14  described above for the schematic of device  10 . Vacuum breaker casing  28  is removable and replaceable. Vacuum breaker casing  28  operatively connects to a source of a second pressurized fluid at pressure P 2  through pipe  19  (not shown, see FIG. 1) and an electronically controlled 3-way valve  12  (not shown, see FIG.  1 ). Female adaptor  30  and pipe  32  make up reservoir  16  (Depicted in FIG.  1 ). To change the volume of reservoir  16 , pipe  32  is removable and changeable so that different lengths of pipe can be used to vary volume. Ball  18  is movably located in vacuum breaker casing  28 , female adaptor pipe  30  and pipe  32 . Tee  36  operatively connects the outlet end of pipe  32  to valves  22  and  24  by threaded or solvent-welded connection, for example. A first inlet  37  of tee  36  contains retaining screw  34  which extends through enough of the diameter to prevent passage of ball  18 . A first threaded nipple  38  operatively connects check valve  22  to a second inlet  39  of tee  36 . Check valve  22  operatively connects a first pressurized fluid source at P 1  (not shown) to device  10  and also is a fluid supply line  23  as depicted in FIG.  1 . Valve  22  prevents backflow into the fluid supply line. Outlet  41  of tee  36  operatively connects to pressure relief valve  24  through reducing bushing  40  and a second threaded nipple  38 . The outlet end of valve  24  is operatively connected to an emitter means for distributing fluids as described above. 
     In another embodiment, device  10  is molded as separate parts which are welded together to make one unit as shown in FIG.  3 . The location of welds, depending on fabrication considerations and the use of standard components, is well within the ordinary skill in the art. For example, in FIG. 3, the float ball restraint  20  and the seat to check valve  22  and valve  24  may be molded into the body or constructed separately and pressed or glued into place. Molded device  10  has a standard externally threaded N.P.T. connection  42  at the inlet end of valve  14  and internally threaded N.P.T. connections  44  at the inlet end of valve  22  and the outlet end of valve  24 . This embodiment is operatively connected to the sources of pressurized fluids and emitter as described above. In this embodiment, casting necessarily fixes the reservoir volume, meaning that different sizes would be cast separately. 
     In operation, during the charging state, signal source  11  (FIG. 1) activates 3-way valve  12 , which shuts off the second pressurized fluid source  13  and allows the first pressurized fluid at pressure P 1  to enter reservoir  16  and pressurized fluid of P 2  is displaced from reservoir  16  to the atmosphere or a recovery vessel (not shown). As reservoir  16  fills, the floating ball  18  seals with valve  14  closing off the inlet end of valve  14 . As pressure in reservoir  16  builds up to pressure P 1 , check valve  22  closes. Reservoir  16  is now charged and ready to be discharged. This is initiated by an electrical pulse from source  11 , which switches the electronically controlled 3-way valve  12 . When valve  12  opens, it releases a second pressurized fluid at pressure P 2 , where P 2 &gt;P 1 , which causes discharge of the reservoir fluid by forcing open pressure relief valve  24  and closing check valve  22  if it is not already closed. The duraton of the pulse is usually determined as the minimum duration required to empty the reservoir. The maximum is whatever is necessary for the application of device  10 . For some applications, it may be desirable for the cycle time to be shorter than that needed to completely fill and empty reservoir  16 . If such a short cycle time is used, the metering device produces a volume per pulse less than the volume of reservoir  16 , depending upon the ratio of the charge time to that for a full charge, and upon the ratio of the discharge time to that for a full discharge. 
     The following examples illustrate the invention and are not intended to limit the scope of the invention as defined by the claims. Tests were conducted with air for the propelling or control fluid at P 2  and water as the dispensed or controlled fluid at P 1 . 
     EXAMPLE 1 
     Tests were conducted to illustrate flow rates and volumes when pressure, discharge time and cycle times are varied. In the first test, air pressure was varied from about 20 psi to about 35 psi, water pressure was about 10 psi, cycle time was about 1.5 seconds and discharge time was about 0.6 seconds. The results are shown in Table 1 below and FIG.  4 . In the second test, discharge time was varied from about 0.4 second to about 1.2 seconds, water pressure was about 10 psi, air pressure was about 30 psi and cycle time was about 3 seconds which allowed reservoir  16  to fully recharge. The results are shown in Table 2 below and FIG.  5 . In the third test, cycle time was varied from about 1.4 seconds to about 2.2 seconds, charge time was varied from about 0.4 second to about 1.2 seconds. In this instance, cycle time equaled charge time plus 1.0 second. Water pressure was about 10 psi, air pressure was about 30 psi and discharge time was about 1 second. The results are shown in Table 3 below and FIG.  6 . In the fourth test, cycle time was varied from about 1.20 seconds to about 2.00 seconds and discharge time was varied from about 0.6 second to about 1.00 second and individual pulse volumes were measured. See Table 4 below for the results. 
     The results of the above tests show that repeatable flow rates and volumes are obtained with several combinations of time when the cycle was short enough that the reservoir did not fill or empty completely. This extends the range of control parameters under which the device performs predictably. Operation above the threshold produces a fixed volume per pulse, yielding a flow rate proportional to the pulse frequency. Operation below the threshold produces flow volumes proportional to the charge and discharge duration as a fraction of the duration allowing full charge/discharge. 
     
       
         
               
             
               
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 VARIABLE AIR PRESSURE 
               
             
          
           
               
                   
                 Water press. = 10 psi 
               
               
                   
                 Cycle time = 1.5 sec 
               
               
                   
                 Discharge time = 0.6 sec 
               
             
          
           
               
                   
                 Volume/10 cycles, ml 
                   
               
             
          
           
               
                   
                 Pressure 
                 Rep 1 
                 Rep 2 
                 Rep 3 
                 Avg. 
                 Std. Dev 
               
               
                   
                   
               
             
          
           
               
                   
                 20 
                 420 
                 425 
                 435 
                 426.7 
                 7.6 
               
               
                   
                 25 
                 725 
                 715 
                 720 
                 720.0 
                 5.0 
               
               
                   
                 30 
                 915 
                 915 
                 920 
                 916.7 
                 2.9 
               
               
                   
                 35 
                 1030 
                 1025 
                 1030 
                 1028.3 
                 2.9 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 VARIABLE DISCHARGE TIME 
               
             
          
           
               
                   
                 Water press. = 10 psi 
               
               
                   
                 Air press. = 30 psi 
               
               
                   
                 Cycle time = 3 sec (this allows time for chamber to fully recharge) 
               
             
          
           
               
                 Discharge time 
                 Volume/10 cycles, ml 
                   
               
             
          
           
               
                 sec. 
                 Rep 1 
                 Rep 2 
                 Rep 3 
                 Avg. 
                 Std. Dev. 
               
               
                   
               
             
          
           
               
                 0.4 
                 560 
                 570 
                 570 
                 566.7 
                 5.8 
               
               
                 0.5 
                 735 
                 735 
                 745 
                 738.3 
                 5.8 
               
               
                 0.6 
                 920 
                 920 
                 910 
                 916.7 
                 5.8 
               
               
                 0.7 
                 1090 
                 1090 
                 1090 
                 1090.0 
                 0.0 
               
               
                 0.8 
                 1280 
                 1285 
                 1285 
                 1283.3 
                 2.9 
               
               
                 0.9 
                 1440 
                 1440 
                 1435 
                 1438.3 
                 2.9 
               
               
                 1.0 
                 1475 
                 1475 
                 1475 
                 1475.0 
                 0.0 
               
               
                 1.1 
                 1490 
                 1490 
                 1495 
                 1491.7 
                 2.9 
               
               
                 1.2 
                 1495 
                 1500 
                 1500 
                 1498.3 
                 2.9 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 VARIABLE DISCHARGE TIME 
               
             
          
           
               
                   
                 Water press. = 10 psi 
               
               
                   
                 Air press. = 30 psi 
               
               
                   
                 Cycle time = 3 sec (this allows time for chamber to fully recharge) 
               
             
          
           
               
                 Discharge time 
                 Volume/10 cycles, ml 
                   
               
             
          
           
               
                 sec. 
                 Rep 1 
                 Rep 2 
                 Rep 3 
                 Avg. 
                 Std. Dev. 
               
               
                   
               
             
          
           
               
                 0.4 
                 560 
                 570 
                 570 
                 566.7 
                 5.8 
               
               
                 0.5 
                 735 
                 735 
                 745 
                 738.3 
                 5.8 
               
               
                 0.6 
                 920 
                 920 
                 910 
                 916.7 
                 5.8 
               
               
                 0.7 
                 1090 
                 1090 
                 1090 
                 1090.0 
                 0.0 
               
               
                 0.8 
                 1280 
                 1285 
                 1285 
                 1283.3 
                 2.9 
               
               
                 0.9 
                 1440 
                 1440 
                 1435 
                 1438.3 
                 2.9 
               
               
                 1.0 
                 1475 
                 1475 
                 1475 
                 1475.0 
                 0.0 
               
               
                 1.1 
                 1490 
                 1490 
                 1495 
                 1491.7 
                 2.9 
               
               
                 1.2 
                 1495 
                 1500 
                 1500 
                 1498.3 
                 2.9 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 INDIVIDUAL PULSE VOLUMES 
               
             
          
           
               
                   
                 Water press. = 10 psi 
               
               
                   
                 Air press. = 30 psi 
               
             
          
           
               
                 Cycle 
                 Discharge 
                 Volume, ml 
                   
               
             
          
           
               
                 time 
                 time 
                 Rep 1 
                 Rep 2 
                 Rep 3 
                 Rep 4 
                 Rep 5 
                 Avg. 
                 St. Dev. 
               
               
                   
               
             
          
           
               
                 2.00 
                 1.00 
                 154 
                 149 
                 149 
                 149 
                 148 
                 149.8 
                 2.4 
               
               
                 1.75 
                 0.80 
                 130 
                 128 
                 128 
                 128 
                 127 
                 128.2 
                 1.1 
               
               
                 1.20 
                 0.60 
                 91 
                 93 
                 92 
                 90 
                 90 
                 91.2 
                 1.3 
               
               
                   
               
             
          
         
       
     
     The foregoing detailed description is for the purpose of illustration. Such detail is solely for that purpose and those skilled in the art can make variations therein without departing from the spirit and scope of the invention. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 INDEX OF THE ELEMENTS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10. Fluid Metering Device 
               
               
                   
                 11. Electronic Control Signal Source 
               
               
                   
                 12. Electronically Controlled 3-Way Valve 
               
               
                   
                 13. Source of Second Pressurized Fluid 
               
               
                   
                 14. Float Check Valve 
               
               
                   
                 16. Fluid Reservoir 
               
               
                   
                 18. Floating Ball 
               
               
                   
                 20. Means for Retaining Ball 
               
               
                   
                 22. Check Valve 
               
               
                   
                 23. Fluid Supply Line 
               
               
                   
                 24. Pressure Relief Valve 
               
               
                   
                 26. Outlet 
               
               
                   
                 28. Vacuum Breaker Casing 
               
               
                   
                 29. Source of First Pressurized Fluid 
               
               
                   
                 30. Female Adaptor (Slip X Thread; FIG. 2) 
               
               
                   
                 32. Pipe 
               
               
                   
                 34. Retaining Screw 
               
               
                   
                 36. Tee (Slip X Slip X Thread; FIG. 2) 
               
               
                   
                 37. First Inlet of Tee 
               
               
                   
                 38. Threaded Nipple 
               
               
                   
                 39. Second Inlet of Tee 
               
               
                   
                 40. Reducing Bushing (Slip X Thread; FIG. 2) 
               
               
                   
                 41. Outlet of Tee 
               
               
                   
                 42. External N.P.T. Connection 
               
               
                   
                 44. Internal N.P.T. Connection