Abstract:
System for determining the flow rate of a fluid and for controlling flow rates. The system provides high resolution with infinite turndown, providing a flow meter which may be used in low flow situations and with fluid additives. The flow rate of an additive fluid is determined in real time with high resolution by providing a novel reciprocating positive-displacement flow meter using magnetically coupled components and a transducer to identify the flow rate of the fluid. A system and method may be incorporated into a flow control system for monitoring the flow rate of a fluid which may be included with an additive delivery system for use with the flowing supply of an additive to be introduced into a flow of untreated fluid in relatively minute quantities.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13,363,012 entitled “Fluid additive delivery system” filed Jan. 31, 2012, to which the priority is claimed. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention provides a system for determining the flow rate of a fluid. The invention may be used for measuring the rate of fluid flow and may be included in a larger system for controlling the flow rate of the fluid. More particularly, the invention provides an improved flow meter which includes a ferrous floating internal piston in a reciprocating flow meter, wherein the internal piston is magnetically tied to a coupling arm with an end in magnetic contact with a linear digital encoding transducer equivalent in operable length to the full stroke of the ferrous floating internal piston and which provides immediate data regarding the smallest movement of the internal piston. 
         [0005]    2. Description of the Related Art 
         [0006]    Systems for measuring fluid flow rates and for introducing measured fluids into flowing fluids are well known. Systems for measuring fluid flow rates are desirable in devices or systems where flow rates must be controlled or verified. Measurement of flow which is accurate, highly precise (high resolution), and consistent is important in various systems utilizing fluid flow for operation. Measurement of those flow rates often must be expressed and communicated in an electronic format that is compatible with programmable logic devices. Moreover, it is desirable to have a high turndown in these systems, although typically one of the most substantial problems with existing meters. Existing meters thus have a narrow (often very narrow) range of operations, problematic in cases of fuel injection where flow may operate between zero flow and high flow rates. 
         [0007]    Systems for delivering fluids, including those for introducing fluids as additives into other fluid flows, are well known in the art and are generally desired where the fluid may have a limited duration of effectiveness after introduction to a flowing untreated fluid, particularly in cases where additives may be selected on site based on the specific need at the time. In some of these applications, it is necessary to precisely control the flow of the metered fluid, such as an additive, relative to the flow of a second fluid, such as fuel, being delivered so as to maintain a ratio of fuel to additive, usually represented in parts per million. This can be particularly critical where the flow of the second fluid is relatively low, driving down the flow rate of the metered fluid. Thus, doing so requires accurate measurement of the additive, particularly where usually delivered at a very low flow rate. 
         [0008]    With regard to addition of a treating agent, the efficacy of the treated fluid may be effected if the proper volume of additive is not introduced to the untreated flow of a process stream at the current flow rate. Additionally, the cost of the additive to be introduced may be quite high, so cost-effectiveness requires the flow rate, as measured by a flow meter and potentially communicated to an associated logic controller which may in turn control the pump supplying the additive. Ensuring consistent delivery of additive to the untreated fluid is a necessity. Introduction of additive at actual flow rates which are above or below the desired flow rate is undesirable, such as in cases where the additive is introduced to an untreated flow of a petroleum-based fluid where combustion may be over- or under-pressurized in the engine, potentially posing a danger to operators and others. Moreover, other additives effect lubricity or conductivity of fuel with each having the need to be injected accurately over a wide (often very wide) range of flow. 
         [0009]    Thus, accuracy, high resolution, and consistency are needed for systems utilizing fluid flow, including systems where additives are used in conjunction with motor and aviation fuels, water-treatment systems, and other systems. 
         [0010]    Among the prior art devices directed to determining the flow rate of a fluid flow, either for determination of flow rates or for addition of a treating agent are positive displacement meters such as oval gear flow meters, which may consist of two close tolerance oval gears which, when fluid is passed between the two, produce a rotary motion within the meter housing. A shaft connected to one of the meter oval gears includes a rotating hall affect sensor that is used to signal the speed of the rotating shaft. A revolution of the shaft represents a certain volume of fluid passing through the meter by virtue of the volumetric displacement between the two gears inside the meter housing. Meters of this type are very sensitive to solids since the tolerances within the meter are very close. Such meters are prone to clogging and locking up as a result of various foreign material found in fluids such as additives or treating agents. In addition, many fluids, additives or treating agents have solids that are a part of the fluid, additive or treating agent itself which tend to be highly abrasive. This abrasiveness quickly wears the meter and causes it to quickly lose efficiency and its ability to accurately reflect the volume passing through the meter. Additives such as dyes are very abrasive with a high solids content making them inappropriate for use with oval gear meters. Many fuel additives are injected at extremely small ratios as low as 1 PPM. Oval gear meters require minimum flow rates that far exceed those rates found in additive injection, making them inoperable in these applications. 
         [0011]    Other prior art metering systems have included float type flow meters that have utilized floats in static, vertically-aligned flows, and reciprocating pistons which have generally measured flow rate according to travel of the reciprocating piston from one end of the associated cylinder to the other. 
         [0012]    Such metering systems are of limited utility in measuring flow rates. Float systems similarly are of limited benefit where the system is susceptible to being out of vertical alignment. 
         [0013]    Where used for additive delivery in fuels, such metering systems are of limited utility, specifically where the volume of additive introduced is particularly small relative of the untreated fluid (such as less (preferably substantially less) than 0.25% or, non-equivalently less than 2500 parts per million (PPM) (additive to fuel)). Substantially higher ratios approach the concept of blending. 
         [0014]    In addition to the foregoing, due to the minute amount of additive dispensed, and the long time needed for the typical reciprocating metering system to complete one cycle (and hence provide a flow rate) that real time flow rates cannot be obtained the resulting flow rate has not assurance that the resulting average is consistent with the dispensing rate throughout the cycle. 
         [0015]    There is therefore a need for an accurate meter flow which performs without reference to the system&#39;s orientation with minimal moving parts. There is also a need for a flow meter with a high turndown, providing a wide range of operation. There is also a need to control the flow rate of a relatively minute volume of additive to be dispensed into a flow of untreated fluid by providing a high resolution additive delivery system, to monitor the flow rate of a fluid with high resolution, or to maintain at high resolution a desired flow rate of additive. 
       SUMMARY OF THE INVENTION 
       [0016]    It is therefore, a principle object of the present invention to provide a flow meter, particularly a positive displacement reciprocating flow meter, which produces accurate metering with minimal moving parts and which is accurate over time, regardless of pump efficiency or system leakage. This achieved by providing a cylindrical body with fluid connectors at its sealed ends, a ferrous floating internal piston, a cylindrical ring freely encircling the cylindrical body and magnetically coupled to the ferrous floating internal piston, a high resolution linear digital encoding transducer (preferably cylindrical and absolute) preferably parallel to and equivalent in length to the cylindrical body, a coupling arm integrally affixed to the magnetic ring so as to function as a single unit therewith and having a magnetic section contacting the linear digital encoding transducer, with a valve system providing additive to reciprocate the ferrous floating internal piston and to dispense additive to the untreated fluid, and a computer adapted to determine the position of the coupling arm relative to said linear digital encoding transducer to determine position, and, by measurement of time and determination of change in direction, velocity and a valve controller to control the valve system to reciprocate the ferrous floating internal piston. The sealed ends of the cylindrical body and the magnetic coupling between the ferrous floating internal piston and the linear digital encoding transducer provide reduce or eliminate leakage and maintenance associated with meters since there are no dynamic seals involved. 
         [0017]    The valve system may have a fluid input from the flowing supply of fluid, such an an additive, a fluid output, and be in fluid communication with a first end connector at one end of the reciprocating flow meter and in fluid communication with a second end connector at the opposite end of the reciprocating flow meter. The valve system may be switchably operable among a first position and a second position to provide for reciprocation of the ferrous floating internal piston. Switching may be accomplished by a valve driven by solenoids or other actuators. In the first position, the fluid input is in communication with the flowing supply of an additive and the fluid output is in communication with the flow of untreated fluid. Thus the first position connects the fluid input and the second end connector and connects the first end connector with the fluid output and the second position connects the fluid input and the first end connector and connects the second end connector with the fluid output. Thus, the valve system is controlled to cause reciprocation of the ferrous floating internal piston between the cylinder first end and the cylinder second end when the piston approaches each end. 
         [0018]    The present flow meter invention, by virtue of its high resolution and infinite turndown, may also be incorporated into a flow control system, such as that for introduction of a flowing additive at a very low ratio of additive fluid to untreated fluid, particularly in cases where a relatively minute volume of additive fluid is to be dispensed into a flow of untreated fluid. The flow meter invention may be used with a pumped supply of additive to monitor and, in conjunction with control of the pump, control the flow of untreated fluid to provide additive at very low ratios of additive to untreated fluid by volume. 
         [0019]    A flow control system incorporating the flow meter invention to control the flow of liquid, such as an additive fluid, may also include an output computer providing an output signal consistent with each flow rate and an fluid flow controller intermediate the supply of fluid and the valve system which can control the flow of fluid into the system, through various flow rates or at least between flowing and non-flowing positions. The fluid flow controller may be a computer-controlled pump, potentially operable among a plurality of pump speeds (which may not need to be quantified) or may be a valve in conjunction with a supply of fluid under pressure. 
         [0020]    In operation, the flow control system may be employed to ensure the appropriate flow rate (such as the ultralow ratios referenced above), regardless of the efficiency or accuracy of the associated additive pump. This may be accomplished by the flow control system receiving a user input for a desired flow rate of additive, which then activates an additive flow controller at an actual flow rate presumed consistent with the desired flow rate of additive. However, as pumps are prone to wear and leakage, resulting in inaccuracies, the method must verify and adjust, as necessary, the actual flow rate. This is accomplished by introducing the presumed flow rate from the pump to a positive displacement reciprocating piston flow meter for verification. 
         [0021]    The flow control system can then compare the presumed flow rate to the output signal to identify the deviation from desired flow rate. Based on determination of this deviation, the flow control system can then adjust the pump&#39;s actual flow rate at the flow controller to obtain the desired flow rate. 
         [0022]    Unlike the prior art, the present flow meter invention provides a high degree of accuracy by providing identification of the position of the piston in the reciprocating flow meter at all points between the ends of the flow meter. This particularly important as it provides an instantaneous, or real time, rate of flow. Thus, the lag time associated with the imprecision of measurements based on the total stroke of the piston through the flow meter is avoided. Delays in time of position data create a corresponding delay in the adjustments necessary to maintain the pre-set ratio. This lag time had historically been a problem in fuel additive delivery systems when the ratio of additive to untreated fluid was less than 1%. In operation, this results in an additive concentration of about 2500 PPM. In the fuel additive industry, anything over 2500 PPM or ¼% is considered blending and may be accomplished with the lower resolution flow meters or a rotary positive displacement device. 
         [0023]    The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    So that the manner in which the described features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only a typical preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0025]      FIG. 1  illustrates the flow meter invention. 
           [0026]      FIG. 2  illustrates the cylinder portion of the flow meter invention. 
           [0027]      FIG. 3  illustrates an alternative embodiment of the flow meter invention 
           [0028]      FIG. 4  illustrates the flow control system incorporating the flow meter invention. 
           [0029]      FIG. 5  illustrates the workflow of the flow control system. 
           [0030]      FIG. 6  illustrates a mechanical actuator at one position for use with the flow meter invention. 
           [0031]      FIG. 7  illustrates the mechanical actuator of  FIG. 6  at a second position for use with the flow meter invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    The present flow meter invention involves the use of magnetically-coupled and sensitive devices to provide precise data to provide an instantaneous high resolution flow meter for monitoring the flow rate of a fluid in real time, even when measured in relatively small units and/or to precisely dispense relatively small volumes of liquid. The flow rate determination provided by the flow meter may be used to control the flow rate of fluid into the flow meter prior to disbursal of the fluid. Similarly, the control over minute volumes of liquid may be used to control the volume of fluid disbursed. 
         [0033]    Preferably, as identified in  FIG. 1 , the flow meter invention  100  performs these functions with high resolution by providing a novel positive-displacement flow meter  102  in fluid communication with a valve system  104  to prompt reciprocation of a piston within the cylinder  132  of the flow meter  102 . The cylinder  132  has a cylinder first end  120  and a cylinder second end  122 , and a first end connector  124  at or about the cylinder first end  120  and a second end connector  126  at or about the cylinder second end  122 . The flow mater invention  100  may also include a guide  220  intermediate the cylinder  132  and the transducer  130 , and parallel to both. Preferably the cylinder  132 , the connectors  124 ,  126 , and the other fluid-conducting components including the orifices through the valve system  104 , the fluid input  108  and the fluid output  110  are of a large diameter compared to the size of particulates carried in or constituting the fluid, providing a ratio of at least 20:1. 
         [0034]    The flow meter invention includes a controller  106 , preferably a programmable logic controller (PLC), receiving signals from the positive-displacement flow meter  102  to identify the flow rate of the fluid. Operation of the valve system  104  may be controlled by any of various types of controllers known in the art, for example, such as with the controller  106  or with a mechanical valve controller drive by the actual flow through the flow meter invention  100 . Positioned near and in alignment with the cylinder  132  is a linear digital encoding transducer  130 . Associated with both the cylinder  132  and the transducer  130  is a coupling arm  118 , having a coupling arm first end  136  and a coupling arm second end  128 . 
         [0035]    The valve system  104  associated with the invention includes a fluid input  108 , having a fluid output  110 , in fluid communication  112 ,  114  with a first end connector  124  of the cylinder  132  and in fluid communication with a second end connector  126  of the cylinder  132 , respectively. This may be a two-position valve, or a combination of valves providing the same effect. As illustrated in  FIG. 1 , the valve system  104  is preferably a four-way, two-position valve positioned by two opposing actuators  134 , preferably solenoids, although two three-way, two-position valves could be used. Alternatively, the second actuator  134  may be replaced with a spring return. Thus, the valve system  104  is switchably operable among a first position  146  and a second position  148 . Switching may be accomplished by one or more solenoid actuators  134  or by other actuators. Preferably, the valve system  104  includes solenoid valves, preferably of the self-cleaning poppet type as these do not utilize wearing surfaces, thus providing a longer system life. 
         [0036]    By virtue of the accuracy of the transducer  130 , the controller  106  may determine the position of the coupling arm  118  relative to the linear digital encoding transducer  130  at all positions between the cylinder first end  120  and the cylinder second end  122 , and may do so in connection with identification of an associated point in time. Beneficially, as the displacement of the piston  204  may be measured by the transducer  130  and as the cross sectional area of the interior of the cylinder  132  is a fixed and known value, the displacement of the piston  204  as measured by the transducer  130  defines the volume of any fluid passing through the system. Thus, the transducer  130  functions like a micrometer, simply telling the system where the piston  204  is relative to the end of the cylinder  132 . As the system (program) knows what the displacement of the cylinder is, a linear unit of measurement therefore represents a fixed amount of fluid. As the distance from the beginning of the stroke is reported, the system knows how much fluid has been displaced. The linear transducer  130  thus serves as a device to measure distance, where distance is directly proportional to volume based on the displacement of the cylinder  132 . Alternatively, the controller  106  may record positions of the coupling arm second end  128  relative to the transducer  130  at associated points in time and may thus determine the speed and direction of movement of the coupling arm second end  128  as a function of change in said position per change in time. The cross-sectional internal area of the cylinder  132  is fixed and constant throughout, so this data also provides the change in volume per unit time, and thus the actual flow rate of the fluid therethrough. 
         [0037]    Referring to  FIG. 2 , the positive displacement flow meter  102  includes a cylinder  132 , a ferrous floating internal piston  204 , a cylindrical ring  206  slidably positioned about and closely encircling the cylinder  132 , a linear digital encoding transducer  130 , and a coupling arm  118  integrally and fixedly associated with the cylindrical ring  206  at its coupling arm first end  136  so as to function as a single unit therewith and in association with the transducer  130 . The coupling arm  118  and the cylindrical ring  206  may be constructed as a single unit and may be formed or created as a single piece. 
         [0038]    The cylinder  132  and internal piston  204  are necessary constituents of a positive displacement reciprocating piston flow meter  102 . The cylinder  132 , composed of a non-ferrous material, has length  212 , a cylindrical (circular tubular) exterior  214 , and a cylinder centerline  216 . The cylinder  132  also has a cylinder axis  222  at the cylinder centerline  216  along the cylinder&#39;s length  212 . The internal piston  204 , composed at least in part of a ferrous material and preferably generates a magnetic field, is freely slidable within the cylinder  132  between the cylinder first end  120  and the cylinder second end  122 . The outer surface of the piston  204  is fitted sufficiently close to the interior of the cylinder  132  to preclude appreciable leakage between the two resulting chambers  228 ,  230  divided by the piston  204 . The piston  204  further has a length  232  sufficient to prevent the piston from binding during movement and thus to maintain its relationship to the cylinder axis  222 . The cylindrical ring  206  is slidably positioned about and closely encircles the cylinder exterior  214 , thus capable of sliding along the cylinder exterior  214  without binding and maintained substantially concentric about the cylinder axis  222 . The cylindrical ring  206  is composed of magnetic material to magnetically couple to the ferrous floating internal piston  204 , but could alternatively be of a ferrous material if the piston generates a magnetic field. Thus, as the piston  204  travels within the cylinder  132 , the cylindrical ring  206  likewise travels and maintains its position relative to the piston  204 . Preferably, a low-friction material  208 , such as a Teflon® ring, may be positioned or inserted between the cylindrical ring  206  and the cylinder  132  to support the cylindrical ring  206 , and to maintain the cylinder ring  206  centered about the cylinder  132 . Preferably, the low friction material  208  is constructed as a ring to fit within the cylindrical ring  206 , but alternatively may be constructed as a sleeve about the cylinder  132 . Alternatively the cylinder exterior  214  and the interior of the cylinder ring  206  may each have a low coefficient of friction so the cylinder ring  206  may freely slide and not be susceptible to increased and undesirable friction by a small number of particulates. Additionally, the cylinder exterior  214  or the interior of cylinder ring  206  may be lubricated to reduce friction. 
         [0039]    A linear digital encoding transducer  130 , preferably absolute, having a transducer length  236  and a transducer axis  238  along its length is also provided. The transducer axis  238  is substantially parallel (preferably parallel) to the cylinder axis  222 . The transducer length  236  is generally equivalent to the cylinder length  212 . Preferably, the transducer axis  238  is generally parallel to the cylinder axis  222 . 
         [0040]    The coupling arm  118  may be integrally affixed to or formed with the cylindrical ring  206  at the coupling arm first end  240  so as to function, preferably permanently, as a single unit therewith and maintained generally perpendicular to the cylinder axis  222 . The coupling arm  210 , which may be constructed of a ferrous metal, includes a magnetic section  244 , which may be a magnet  250  or a magnetized section, at the coupling arm second end  242  of sufficient strength to generate a magnetic field contacting or interacting with the linear digital encoding transducer  130  as it rides over or about the transducer  130  to indicate the position of the coupling arm  118  (and thus the cylindrical ring  206 ) relative to the transducer  130 . This may be accomplished by a single arm riding adjacent the transducer  130  or by a section of coupling arm second end  128  or a cylindrical ring integrally affixed to or formed with the cylindrical ring  206  at the coupling arm second end  128  so as to function, preferably permanently, as a single unit therewith, having an opening to encircle the transducer  130 . By avoiding a mechanical couple between the piston  204  and the transducer  130 , seals through the cylinder first end  120  or the cylinder second end  122  are avoided, particularly as each seal are prone to leakage and may result in unequal operation as the piston  204  reciprocated in the cylinder  132 . By avoiding a mechanical couple, the risk of contact by the couple with other metal components, a fire hazard, and the need for additional components to transform the mechanical couple&#39;s movement to movement along the transducer  130  are avoided. 
         [0041]    Positioning the transducer  130  separate from the cylinder  132 , rather than directly in contact or immediately adjacent, is necessary for the accuracy of the transducer  130 . Positioning the transducer  130  separate from the cylinder  132  ensures the magnetic field of the internal piston  204  does not interfere with the accuracy of the transducer  130 , which utilizes a magnetic field to determine the slightest change in position of the internal piston  204  via the coupling arm  118 . Separation, together with the transducer-encircling segment of coupling arm second end  128 , provides accurate readings, particularly of the accuracy needed incident to the potentially quite low flow rates involved. This is particularly important as the transducer  130  necessarily must provide a high degree of accuracy with respect to each movement of the piston  204 , preferably in the precision of about 1/1,000 of an inch of travel, rather than the per cycle signal associated with the prior art. The movement over the transducer may be of length selected in light of the fluid, flow rate and length of stroke desired in the flow meter, whether it be 3 inches, 10 inches or 20 inches. 
         [0042]    Since the floating internal piston  204  and coupling arm  118  are magnetically coupled, as the floating internal piston  204  moves along the length of the metering cylinder  132 , the coupling arm  118  is carried precisely at the same relative position along the length  236  of the linear digital encoding transducer  130 . The linear digital encoding transducer  130  translates the relative position of the magnetic section  244  of the coupling arm  210  into an electrical signal which is communicated to the controller  106 , which may be a programmable logic controller. 
         [0043]    A guide  220  is preferably used and positioned intermediate the cylinder  132  and the transducer  130 , and parallel to both. The guide  220  limits the motion of the coupling arm  118  to a plane parallel to both the cylinder  132  and the transducer  130 , reducing the likelihood of the coupling arm  118  binding about the cylinder  132  and the transducer  130 . This limitation may be accomplished, for example, by the coupling arm  118  encircling the cross section of the guide  220  as depicted in  FIGS. 1 and 2 , or the coupling arm  118  having a track on its periphery mating to the guide  220 . The guide  220  may provide a low friction point of contact and may be a flat plate. Regardless of its construction, the guide  220  maintains the magnetic section  244  of the coupling arm second end  128  about the transducer  130 , preferably concentrically, without contacting the transducer  130 . 
         [0044]    Referring again to  FIG. 1 , the controller  106  may also control the valve system  104  to reciprocate the ferrous floating internal piston  204  between the cylinder first end  120  and the cylinder second end  122  at least when the piston  204  approaches, nearly reaches or reaches the cylinder first end  120  or the cylinder second end  122 . The valve system  104  may accomplish this by generating an electric pulse to cause one of the solenoids  134  or another actuator  134  to change position. 
         [0045]    Alternatively, as illustrated in  FIG. 3 , the cylinder  132  may have, exiting through either its cylinder first end  120  or its cylinder second end  122 , a first rod  302  coupled to the valve system  104  at an actuator  134  to effect flow reversal at the end of the stroke, that is when the piston  204  reaches or nearly reaches the cylinder first end  120  or the cylinder second end  122 . A matching second rod  303 , not coupled to any device, would necessarily exit the cylinder  132  at its opposite side and be similarly related to the piston  204  to ensure the volumes of the two chambers  228 ,  230 , and therefore their displacement, are equivalent. The first rod  302  is preferably coupled to the piston  204  to ensure motion in both directions, but could be loaded, such as by a spring, to move with the piston  204 . In one embodiment, this could be accomplished with a snap action, spring-loaded shifter to work with a single actuator, such as depicted in  FIGS. 6 and 7 . Alternatively, a three-way valve could be coupled to each of the two rods  302 ,  303  to effect operation. 
         [0046]    With reference to  FIGS. 6 and 7 , an automatic shifting mechanism  600 , that shifts the valve system  104  via and in response to the movement of first rod  302  among the first position  146  and the second position  148 , thus also reversing the direction of movement of the piston  204  in the flow meter  102 . 
         [0047]    As shown in more detail in  FIG. 6 , yoke  606  and a lever  610  are commonly mounted on a bushing  616  fixed to a stationary standard  614 . The yoke  606  is shown in an retracting (not upward) position. Yoke  606  and lever  610  are free to independently rotate about bushing  616 , except that a torsion spring  608  resiliently couples the free end of lever  610  with an internal arm  618  in yoke  606 . The free end of lever  610  is coupled to linkage arm  620  by ball joint connection  612 . Pin  602 , located at the end of first rod  302 , is captured and slides within a narrow neck  604  of yoke  606  and causes yoke  606  to rotate about bushing  616 . 
         [0048]    In  FIG. 6 , first rod  302  has reached its outermost limit of travel, and the yoke  606  has actuated to cause lever  610  to be in the downward position. The flow meter  102  has reversed and first rod  302  reverses direction, retracting. As pin  602  moves toward flow meter  102 , yoke  606  rotates clockwise about bushing  616 , causing internal arm  618  to rotate clockwise. Such clockwise rotation compresses torsion spring  608 . The force exerted by torsion spring  608  upon ball joint  612  is still in the direction of retraction. As the first rod  302  approaches its point of travel furthest in retraction, the internal arm  618  is horizontally aligned with ball joint  612  and torsion spring  608  is at maximum compression. Any further motion toward flow meter  102  by first rod  302  causes torsion spring  608  to present an outward force on ball joint  612 , which rapidly snaps to its upper position, thereby changing the positions of valve system  104  and changing the direction of fluid flow into flow meter  102 . 
         [0049]      FIG. 7  shows yoke  606  of the automatic shifting mechanism in the retracted position. As first rod  302  extends, the torsion spring  608  compresses against ball joint  612  in the outward direction until internal arm  618  is horizontally aligned (i.e. reaches minimum distance) with ball joint  612 . Ball joint  612 , carrying linkage arm  620  then snaps back into the retracting position, thus completing the cycle. 
         [0050]    Referring again to  FIGS. 1 and 2 , since the change in volume of each chamber  228 ,  230  of the metering cylinder  132  is calculated based on change in position, each thousandths of an inch in length of each chamber  228 ,  230  the metering cylinder  202  corresponds to a position on the linear digital encoding transducer  130 , and therefore accurately represents the flow passing through the flow meter loop  116 . Preferably, when the floating internal piston  204  reaches an end of the metering cylinder  120 ,  122 , and when the controller  106  is used to control the valve system  104 , the signal from the linear digital encoding transducer  130  as processed by the controller  106  to effect a change in position of the valve system  104  among the first and second positions  146 ,  148  (such as by activating the solenoid actuator  134  to change its position), changing the direction of flow from one end of the metering cylinder to the opposite end  120 ,  122 . 
         [0051]    Thus, in operation the fluid from the fluid input  108 , and the associated pressure, entering the metering cylinder  132  works against the floating piston  204 , and drives the fluid on the opposing, and now discharging, side of the floating piston  204  to be discharged by valve system  104 . This is accomplished by ensuring in the first position  146 , the fluid input  108  is connected to the second end connector  126  and the first end connector  124  is connected to the fluid output  110 . In the second position  148 , the fluid input  108  is connected to the first end connector  124  and the second end connector  126  is connected to the fluid output  110 , thus reversing the flow of fluid through the flow meter loop  116 , and reversing the direction of movement of the piston  204 . 
         [0052]    Due to the large diameter of the metering cylinder  202  and the orifice diameters throughout the meter, the invention  100  is very tolerant of solids and abrasives and thus provides longer life in addition to improved accuracy. Thus, the metering device  100  is unique in that it does not rely on close tolerance meshing machined parts in order to measure the flow of fluid. 
       Flow Control System 
       [0053]    Because the flow meter invention  100  provides precise determination of the flow rate of a fluid and/or volume of distribution, it may be incorporated into a flow control system  400 , such as depicted in  FIG. 4 , such that the fluid output  110  from the flow meter invention  100  may be discharged where desired, including being introduced into a second fluid  402  as an additive for blending. 
         [0054]    The flow control system  400  integrates the flow meter invention  100  intermediate a source  404  of fluid and a destination  450 . The source  404  of fluid to be metered, such as an additive, in a supply  406  may be connected to the fluid input  108  of the flow meter invention  100  and may be permitted to introduce the fluid to the fluid input  108 . The controller  106  may then provide an output signal consistent with the associated flow rate to a flow controller  408 , operable at least among a fluid flowing position and a fluid non-flowing position, intermediate the supply  406  and the valve system  104 . The flow controller  408  may be a computer-controlled pump, including one operable among a plurality of pump speeds, or a valve. The fluid supply  406  may be any type of fluid source, including one flowing and one of fixed volume, which may or may not be under pressure. The destination  450 , in communication with the output  110  from the valve system  104  (preferably through an injection point check value  452  to prevent contamination or backflow pressure in the system) may be another volume, a container, or even a flow of untreated fluid for introduction of an additive or for blending. 
         [0055]    In operation, the flow control system  400  may be employed to ensure the desired flow rate of an additive fluid is actually obtained. This may be accomplished by the flow control workflow  500 . 
         [0056]    At step  502 , the system receives a user input for said desired flow rate of additive fluid and a desired quantity. 
         [0057]    At step  504 , the system activates the additive flow controller  408  at a presumed flow rate consistent with said desired flow rate of additive fluid. 
         [0058]    At step  506 , the system introduces the additive fluid at presumed flow rate to the flow meter invention  100  via the valve system  104  as controlled by the controller  106 . 
         [0059]    At step  508 , controller  106  determines the actual flow rate via the movement of the ferrous floating internal piston  204 , i.e. based on position related to displacement (particularly based on the relative position along the length of the transducer), and provides at least one output signal consistent with the actual associated flow rate to the system. 
         [0060]    At step  510 , the system determines if the actual flow rate is within the margin of error of the desired flow. If the actual flow rate is within the margin of error of the desired flow rate, the system proceeds to step  514 . Otherwise, the system continues to step  512 . 
         [0061]    At step  512 , the system adjusts the actual flow rate at said additive flow controller  408  to obtain the desired flow rate from step  502 . 
         [0062]    At step  514 , the system determines if the desired quantity of additive fluid has been provided, which may be based on the actual flow rate(s) and elapsed time(s) or may be based on the displacement of the piston  204  as measured by the transducer  130 . If the system determines if the desired quantity of additive fluid has been provided, the method ends. If not, the system returns to step  508 . 
         [0063]    The resulting system  400  may provide delivery of the fluid to ensure delivery from a flowing supply of a fluid into a flow of a second fluid at a low ratio consistent with additive treatment. 
         [0064]    While the present invention has been described in connection with presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the invention to those embodiments. It is therefore, contemplated that various alternative embodiments and modifications may be made to the disclosed embodiments without departing from the spirit and scope of the invention defined by the appended claims and equivalents thereof.