Patent Publication Number: US-10766046-B2

Title: Mix on demand smart backpack sprayer with removable concentrate tank

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of pending U.S. patent application Ser. No. 16/156,284 filed Oct. 10, 2018, entitled “MIX ON DEMAND SMART BACKPACK SPRAYER,” which is a continuation-in-part of pending U.S. patent application Ser. No. 15/725,937 filed Oct. 5, 2017, entitled “MIX ON DEMAND SPRAYER,” the contents of both of which are fully incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to a sprayers, and more particularly to a sprayer configured to dilute a fluid concentrate with a diluent prior to spraying, and still more particularly to a mixing manifold selectively and changeably metered to inject a measured dose of the fluid concentrate into the diluent to produce a mixed fluid with a desired concentrate dilution. In a further aspect of the present invention, the present invention generally relates to backpack sprayers, and more particularly to a backpack sprayer incorporating smart controls and enhanced fluid control systems, and still more particularly to a backpack sprayer including a removable and swappable fluid concentrate tank. 
     BACKGROUND OF THE INVENTION 
     Sprayers, such as broadcast sprayers are used across an array of applications, including farms, golf courses and residential properties, to apply water or other liquids, such as pesticides including herbicides, insecticides and the like. As such, these sprayers may need to cover a large area and, therefore, generally include large tanks strapped to a vehicle, such as an all-terrain vehicle (ATV) or golf cart, or may be mounted onto a tow-behind trailer. Typically in use, these tanks are filled with a selected fluid composition that is to be applied. By way of example, pesticide solutions may be anywhere from about 1% to about 10% active chemical in water. In one scenario, a user may spray a diluted herbicide solution, such as to target thistle. However, to apply a second pesticide solution, such as a diluted insecticide to fruit trees, the user will first have to completely empty the tank of the herbicide solution before rinsing the tank of any residual chemicals and finally refilling the tank with the desired insecticide solution. As may be readily apparent from the above, there are numerous drawbacks to such systems. For example and without limitation, such drawbacks may include waste of chemicals, the need for controlled disposal of unused chemicals, the time consuming need to thoroughly clean the tank between applications and the potential for cross-contamination and application of unwanted chemicals after incomplete or unsuccessful cleaning of the tank. 
     To alleviate some of the above-referenced drawbacks of broadcast sprayers, systems have been developed which segregate the chemical portion from the water/diluent portion of the system. In such systems, the chemical is stored in a smaller, separate tank than the large water tank. Metering devices may then add chemical to a flow of water prior to emission from a wand or boom sprayer. In this manner, the chemical remains isolated from the water tank, thereby minimizing or avoiding possible contamination of the water source. However, heretofore systems require complex plumbing regimes and interconnectivities of the various components making such systems difficult to use and burdensome to operate and clean. 
     Broadcast sprayers have also been configured as variable pressure sprayers which may selectively spray fluid from either a spray wand or through a boom-and-nozzle arrangement where multiple nozzles may be supported on a boom. Due to the multiple nozzles within the boom-and-nozzle arrangement, fluid must be delivered at high pressure so as to enable proper spraying at each of the individual nozzles. However, a spray wand uses a single nozzle and may become damaged if it receives high pressure fluid. To that end, current systems typically use pumps with a high pressure cut out switch. These systems are configured with a recirculation manifold whereby excess flow from the pump is diverted back to the supply tank. A valve and pressure gauge is provided on the manifold so the user can tune the percentage of flow going back to the tank while maintaining adequate pressure for the lower flow application (spray wand). Without providing for this recirculation pressure bleed off in the low flow application, pressure would build quickly and rapidly cycle the pressure cut off switch. A situation that is detrimental to both the switch and the pump. However, such a system should not be used in two-tank systems as the mixed fluid exiting the pump would be recycled to the water tank, thereby contaminating the water tank and changing the concentration of the chemical that is being sprayed. 
     Beyond broadcast sprayers, backpack sprayers are also used to apply water or other liquids, such as pesticides including herbicides, insecticides and the like. As the name implies, backpack sprayers are designed to be worn by the user, such as through securing a tank of the sprayer against the user&#39;s back via one or more shoulder straps. A handheld spray wand is fluidly coupled to the tank and is manually actuated, such as through a trigger, to dispense fluid from the tank through the spray wand. Backpack sprayers may be configured as battery-powered, variable pressure pump sprayers that may selectively spray fluid from the spray wand at different pressures. Typically, a positive displacement pump, such as a diaphragm pump, is powered by the battery to draw fluid from the various fluid tanks and deliver the pressurized fluid to the wand nozzle to be sprayed. However, currently available backpack sprayers only afford spraying at differing pressures and do not allow the chemical/diluent ratio to be changed. 
     Thus, there remains a need for a backpack sprayer with smart controls that also segregates the chemical tank from the water tank while providing selective and variable dilution of the chemical during application. The present invention satisfies this as well as other needs. 
     SUMMARY OF THE INVENTION 
     In view of the above and in accordance with an aspect of the present invention, the present invention is generally directed to a sprayer system comprising a first tank configured to hold a diluent; a mounting bracket mounted to the first tank; and a second tank removably mounted to the first tank and configured to hold a liquid concentrate. A mixing manifold is mounted to the mounting bracket and has a first inlet fitting configured to receive a fixed amount of diluent from the first tank and a second inlet configured to receive a selectively adjustable amount of liquid concentrate from the second tank. The fixed amount of diluent and selectively adjustable amount of concentrate are combined to form a mixed solution. The mixing manifold includes a mixed solution outlet and a positive displacement pump is mounted to the mounting bracket and has a suction port fluidly coupled to the mixed solution outlet. A pressure port is configured to fluidly couple with a spray device. The second tank may be separable from the first tank without requiring removal of the mixing manifold or positive displacement pump. 
     In a further aspect of the present invention, the positive displacement pump is a diaphragm pump and the first inlet fitting further includes a check valve configured to prevent backflow of the mixed solution toward the first tank. 
     In still another aspect of the present invention, the mixing manifold further includes a disc defining a first annular series of spaced-apart flow-metering holes. Successive respective flow-metering holes have an increasing hole diameter and the disc is adapted to rotate to align a selected flow-metering hole in fluid communication with the second inlet to thereby define the selectively adjustable amount of concentrate in the mixed solution. The disc may further define a second annular series of spaced-apart stop holes. Each respective stop hole within the second annular series radially aligns with a respective flow-metering hole of the first annular series. A single respective stop hole receives a stop member when the selected flow-metering hole is aligned with the second inlet. The stop member may be a ball bearing biased to engage the disc wherein a diameter of the ball bearing is slightly larger than a diameter of each of the stop holes. 
     In another aspect of the present invention, the first inlet fitting may further include a check valve configured to prevent backflow of the mixed solution toward the first tank and the second tank may be removably mounted to the mounting bracket on the first tank. 
     In still a further aspect of the present invention, the second tank may include a quick disconnect coupling configured to releasably couple a concentrate tube to a tank fitment defined on the second tank. The concentrate tube may then deliver the liquid concentrate to the mixing manifold. The quick disconnect coupling may comprise a fitment housing having a first end, a second end and a stepped bore region therebetween, wherein the first end is coupled to the tank fitment defined on the second tank. A tubing nut may be removably coupled to the second end of the fitment housing and a tubing coupling may be configured to be received within the tubing nut and abut against a mouth opening defined by the second end of the fitment housing. A plug member may have a plug end, a flanged end and a body portion therebetween. The plug end may be received in the first end of the fitment housing while the flanged end may be received within the second end of the fitment housing and the body portion may extend through the stepped bore region of the fitment housing. A biasing member may also be received within the stepped bore region, wherein the biasing member urges the plug end of the tubing coupling to seal the first end of the fitment housing when the tubing nut is removed from the second end of the fitment housing. A biasing force is stored within the biasing member by the flanged end when the tubing nut is coupled to the second end of the fitting housing, whereby fluid concentrate within the second tank can flow through the quick disconnect coupling to the mixing manifold. The body portion of the plug member may comprise a plurality of spaced apart spindles with open slots defined therebetween to permit flow of fluid concentrate therethrough. 
     In yet another aspect of the present invention, the sprayer system may further include a pressure by-pass recirculation loop fluidly coupling the pressure port to the suction port. The pressure by-pass recirculation loop may be configured to selectively regulate a fluid pressure of the mixed solution being delivered to the spray device. The pressure by-pass recirculation loop may be either internal to the positive displacement pump or an external pathway around the positive displacement pump. 
     In accordance with another aspect of the present invention, the present invention is generally directed to a sprayer system comprising a first tank configured to hold a diluent; a mounting bracket mounted to the first tank; and a second tank removably mounted to the first tank and configured to hold a liquid concentrate. A mixing manifold is mounted to the mounting bracket and has a first inlet fitting configured to receive a fixed amount of diluent from the first tank and a second inlet configured to receive a selectively adjustable amount of liquid concentrate from the second tank. The fixed amount of diluent and selectively adjustable amount of concentrate are combined to form a mixed solution. The mixing manifold includes a mixed solution outlet and a positive displacement pump is mounted to the mounting bracket and has a suction port fluidly coupled to the mixed solution outlet. A pressure port may be fluidly coupled to at least one spray device. The second tank may be separable from the first tank without requiring removal of the mixing manifold or positive displacement pump. The at least one spray device may be a low pressure spray nozzle or a high pressure boom carrying two or more boom nozzles. Alternatively, the at least one spray device is a low pressure spray nozzle and a high pressure boom carrying two or more boom nozzles whereby the mixed fluid is selectively received by either the low pressure spray nozzle or the high pressure boom. The sprayer system may further include a pressure by-pass recirculation loop fluidly coupling the pressure port to the suction port. The pressure by-pass recirculation loop may be configured to selectively regulate a fluid pressure of the mixed solution being received by the low pressure spray nozzle. The pressure by-pass recirculation loop may be either internal to the positive displacement pump or an external pathway around the positive displacement pump. 
     In view of the above and in accordance with an aspect of the present invention, the present invention is generally directed to a backpack sprayer system including a mounting bracket having a battery receiving fixture to receive a battery therein. A first tank is mounted to the mounting bracket and holds a diluent. A second tank is mounted to the mounting bracket and holds a liquid concentrate. A mixing manifold is mounted to the mounting bracket and has a first inlet fitting to receive a fixed amount of diluent from the first tank and a second inlet to receive an adjustable amount of liquid concentrate from the second tank. The fixed amount of diluent and adjustable amount of concentrate are combined to form a mixed solution and the mixing manifold includes a mixed solution outlet. A positive displacement pump is mounted to the mounting bracket and a suction port coupled to the mixed solution outlet and a pressure port fluidly coupled with a spray device. A control unit is mounted on the mounting bracket and receives power from the battery. The positive displacement pump may be a diaphragm pump. The first inlet fitting may also include a check valve configured to prevent backflow of the mixed solution toward the first tank. 
     In a further aspect of the present invention, the mixing manifold further includes a disc defining a first annular series of spaced-apart flow-metering holes. Successive respective flow-metering holes have an increasing hole diameter and the disc is adapted to rotate to align a selected flow-metering hole of the annular series of spaced-apart holes in fluid communication with the second inlet to thereby define the selectively adjustable amount of concentrate in the mixed solution. The disc may further define a second annular series of spaced-apart stop holes. Each respective stop hole within the second annular series radially aligns with a respective flow-metering hole of the first annular series. A single respective stop hole receives a stop member when the selected flow-metering hole is aligned with the second inlet. The stop member may be a ball bearing biased to engage the disc, wherein a diameter of the ball bearing is slightly larger than a diameter of each of the stop holes. 
     In still another aspect of the present invention, a battery may be removably secured within the battery receiving fixture. The battery is operably coupled to the positive displacement pump and control unit whereby the battery is configured to provide power to the positive displacement pump and control unit when the sprayer system is in an on configuration. 
     In another aspect of the present invention, the second tank is fixedly secured within the first tank, whereby an open volume defined by the second tank is fluidly isolated from an open volume defined by the first tank. The second tank may also include a concentrate fitting configured to receive a first end of a concentrate tube. The second end of the concentrate tube is coupled to the second inlet of the mixing manifold. The first tank may also include a diluent fitting configured to receive a first end of a diluent tube. The second end of the diluent tube is coupled to the first inlet of the mixing manifold. The second tank may further include a liquid level gauge. 
     In still a further aspect of the present invention, the control unit comprises a printed circuit board and a control panel interface. The printed circuit board includes a processor and a memory, wherein the processor is configured to perform one or more functions including power on/power off, regulating power to the positive displacement pump so as to vary output pressure of the mixed solution, monitoring and displaying a battery charge level, and indicating pacing. The control panel interface is coupled to the printed circuit board and includes one or more control buttons whereby a user may selectively control the processor functions. 
     In view of the above and in accordance with a further aspect of the present invention, the present invention is generally directed to a backpack sprayer system including a mounting bracket having a battery receiving fixture to receive a battery therein. A first tank is mounted to the mounting bracket and holds a diluent. A second tank is mounted to the mounting bracket and holds a liquid concentrate. The second tank is separable from the first tank and is selectively, individually removable from the mounting bracket. A mixing manifold is mounted to the mounting bracket and has a first inlet fitting to receive a fixed amount of diluent from the first tank and a second inlet to receive an adjustable amount of liquid concentrate from the second tank. The fixed amount of diluent and adjustable amount of concentrate are combined to form a mixed solution and the mixing manifold includes a mixed solution outlet. A positive displacement pump is mounted to the mounting bracket and a suction port coupled to the mixed solution outlet and a pressure port fluidly coupled with a spray device. A control unit is mounted on the mounting bracket and receives power from the battery. 
     Additional objects, advantages and novel aspects of the present invention will be set forth in part in the description which follows, and will in part become apparent to those in the practice of the invention, when considered with the attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a sprayer system in accordance with an aspect of the present invention; 
         FIG. 2  is an exploded view of the sprayer system shown in  FIG. 1 ; 
         FIG. 3  is a front perspective view of the sprayer system shown in  FIG. 1  with the diluent tank removed; 
         FIG. 4  is a rear perspective view of the sprayer system shown in  FIG. 3 ; 
         FIG. 5  is an exploded view of a liquid concentrate tank used within the sprayer system shown in  FIG. 1 ; 
         FIG. 6  is a cross section view of the liquid concentrate tank used within the sprayer system shown in  FIG. 1 ; 
         FIG. 7  is a cross section view of a tubing fixture used with the liquid concentrate tank shown in  FIG. 5 ; 
         FIG. 8  is an exploded cross section view of the tubing fixture shown in  FIG. 7 ; 
         FIG. 9  is a top perspective view of a mixing manifold used within the sprayer system shown in  FIG. 1 ; 
         FIG. 10  is a bottom perspective view of the mixing manifold shown in  FIG. 9 ; 
         FIG. 11  is a top front exploded view of the mixing manifold shown in  FIGS. 9 and 10 ; 
         FIG. 12  is a bottom front exploded view of the mixing manifold shown in  FIGS. 9 and 10 ; 
         FIG. 13  is a cross section view of the mixing manifold, taken generally along line  13 - 13  in  FIG. 9 ; 
         FIG. 14  is an isolated view of a disc used within the mixing manifold shown in  FIGS. 9 through 13 ; 
         FIG. 15  is a schematic view of a pressure by-pass system suitable for use within a variable pressure sprayer system in accordance with an aspect of the present invention; 
         FIG. 16  is a front perspective view of a sprayer system in accordance with an aspect of the present invention; 
         FIG. 17  is a rear perspective view of the sprayer system shown in  FIG. 16 ; 
         FIG. 18  is a bottom front perspective view of the sprayer system shown in  FIG. 16 ; 
         FIG. 19  is a front elevational view of the sprayer system shown in  FIG. 16 ; 
         FIG. 20  is a cross section view of the sprayer system, taken generally along line  20 - 20  in  FIG. 19 ; 
         FIG. 21  is a bottom plan view of the sprayer system shown in  FIG. 16 ; 
         FIG. 22  is a longitudinal cross section view the sprayer system shown in  FIG. 19 ; 
         FIG. 23  is top plan view of the sprayer system shown in  FIG. 16 ; 
         FIG. 24  is an exploded view of the sprayer system shown in  FIG. 16 ; 
         FIG. 25  is a plan view of a control panel interface configured for use with the sprayer system shown in  FIG. 16 ; 
         FIG. 26  is a front perspective view of an alternative embodiment of a sprayer system in accordance with an aspect of the present invention; 
         FIG. 27  is an exploded view of the sprayer system shown in  FIG. 26 ; 
         FIG. 28  is a side cross section view of the sprayer system shown in  FIG. 26 ; 
         FIG. 29  is an expanded cross section view of a clamp used within the sprayer system shown in  FIG. 26 ; and 
         FIG. 30  is a bottom view of the sprayer system shown in  FIG. 26 , with the positive displacement pump removed to more clearly show system tubing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1 and 2 , in accordance with an aspect of the present invention, sprayer system  10  may generally comprise a first tank  12 , mounting bracket  14 , second tank  16 , mixing manifold  38  and positive displacement pump  42 , such as and without limitation thereto, a diaphragm pump. Mounting bracket  14  may be mounted to first tank  12 , such as via mechanical fasteners  18 . To provide further support and to resist lateral movement of mounting bracket  14  in the x-z plane, first tank  12  may include a tang  20  configured to reside within a notch  22  defined within mounting bracket  14 . Second tank  16  may be mounted to first tank  12  and mounting bracket  14 , such as via a strap (not shown). To that end, second tank  16  may include a strap recess  24  configured to receive the strap and first tank  12  may further include a strap tie down clamp  26  whereby movement of second tank  16  in the y-axis is prohibited. To minimize lateral displacement of second tank  16  (i.e., in the x-z plane) mounting bracket  14  may include one or more upwardly extending nodules  28  configured to coincide with matching indentations  30  defined on bottom wall  32  of second tank  16  (see  FIG. 6 ). In this manner, a user may unfasten the strap and lift second tank away from mounting bracket  14  and first tank  12 , such as via handle  17 , without requiring the use of tools. Strap tie down clamp  26  may further include a wand receiving portion  34  defining a wand receiving recess  36  whereby a spray wand (not shown) may be releasably coupled to sprayer system  10  when the spray wand is not in use. With continued reference to  FIGS. 1 and 2 , and with additional reference to  FIGS. 3 and 4 , a mixing manifold  38  may be mounted to mounting bracket  14 , such as via mechanical fasteners  40 , and positive displacement pump  42  may be mounted to mounting bracket  14  such as via mechanical fasteners  44 . In this manner, each of the second tank  16 , mixing manifold  38  and positive displacement pump  42  may be individually and separately removed from mounting bracket  14  and first tank  12 . 
     In operation, first tank  12  includes a diluent outlet  46  having a diluent fitting  47  configured to receive one end of diluent tubing (not shown) in a substantially fluid-tight seal. The opposing end of the diluent tubing is mounted onto a first inlet fitting  48  of mixing manifold  38  (see also  FIGS. 9-13 ). First inlet fitting  48  may include a tapered nipple  50  and ribbed portion  52  so as to snuggly receive the diluent tubing thereon in a substantially fluid-tight seal. An optional hose clamp (not shown) may also be used to more securely clamp the diluent tubing to ribbed portion  52 . Mixing manifold  38  may further include a second inlet  54  configured to receive concentrate tubing (not shown) from second tank  16 . As shown most clearly in  FIGS. 4 and 10 , mixing manifold  38  may include a notch  56  proportioned to permit passage of concentrate tubing through housing  58  of mixing manifold  38 . Mounting bracket  14  may also include a recess  60  to accommodate passage of the concentrate tubing (see  FIGS. 2 and 4 ). Thus, a first end of the concentrate tubing may be mounted to fitment  62  housed within second inlet  54 . The concentrate tubing may then extend toward second tank  16  wherein the opposing end of the concentrate tubing is mounted to second tank  16  via concentrate outlet fitting  64 . 
     With reference to  FIGS. 5 and 6 , second tank  16  may be filled with a selected fluid concentrate through tank opening  19  defined by a threaded mouth portion  21 . A cap  23  may be removably threaded onto mouth portion  21  so as to seal second tank  16 . An optional O-ring  25  may also facilitate a fluid-tight seal between second tank  16  and cap  23 . To prevent clogging of downstream plumbing components, mouth portion  21  may further receive filter element  27  therein. When filling second tank  16  with fluid concentrate, the fluid will pass through filter element  27  whereby particulate matter larger than the pore size of the filter element will be strained out of the fluid. Accordingly, the pore size of filter element  27  should be selected so as to be smaller than the internal diameter of the smallest diameter downstream component, such as disc  168  which will be discussed in greater detail below. 
     With reference to  FIGS. 7 and 8 , to facilitate tool-less removal of second tank  16  from mounting bracket  16  and mixing manifold  38 , concentrate outlet fitting  64  may be a quick disconnect coupling generally comprised of a fitment housing  66  having a first end  68  configured to be threadably coupled to a corresponding tank fitment  70  defined on second tank  16  (see  FIG. 5 ). First end  68  of fitment housing  66  may also be configured to receive a tank tubing coupling  72  whereby tank tubing coupling  72  includes a flanged end  74  proportioned to abut against mouth opening  76  of tank fitment  70  such that tank tubing coupling  72  is entrapped between mouth opening  76  and stepped wall  78  of fitment housing  66  when fitment housing  66  is threaded onto tank fitment  70 . To promote a fluid-tight seal between tank fitment  70  and fitment housing  66 , one or more seals, such as O-rings  80 ,  82  may be included. The opposing end of tank tubing coupling  72  may include one or more barbs  84  dimensioned to snuggly receive a concentrate pick-up tube (not shown) which may extend from tank tubing coupling  72  to proximate bottom wall  32  of second tank  16 . In this manner, liquid concentrate may be drawn from second tank  16  as will be described in greater detail below. 
     With continued reference to  FIGS. 7 and 8 , second end  86  of fitment housing  66  may include male threads  88  configured to threadably engage female threads  90  defined within a first end  92  of tubing nut  94 . Second end  86  may further define a bore  96  dimensioned to receive a first end  98  of a concentrate tubing coupling  100  therein upon threaded engagement of tubing nut  94  with fitment housing  66 . The opposing end  102  of concentrate tubing coupling  100  may include one or more barbs  104  dimensioned to snuggly receive the opposing end of the concentrate tubing as described above. Annular flange  106  on concentrate tubing coupling may engage seat portion  95  of tubing nut  94  such that tubing nut  94  may permit mounting of concentrate tubing coupling  100  to second tank  16  with minimal, if any, twisting of the concentrate tubing as tubing nut  94  is rotatably threaded onto male threads  88 . To assist in properly seating concentrate tubing coupling  100  within fitment housing  66 , annular flange  106  may also be dimensioned to abut against the mouth opening  110  of bore  96  when tubing nut  94  is fully tightened. An O-ring seal  112  may also promote a fluid-tight seal between concentrate tubing coupling  100  and bore  96  of fitment housing  66 . 
     In a further aspect of the invention, bore  96  may be further include a series of steps  114 ,  116 ,  118  thereby defining bore regions  96   a ,  114   a ,  116   a ,  118   a . Concentrate tubing coupling  100  may reside within bore region  96   a  such that terminal end  120  of first end  98  of concentrate tubing coupling  100  may seat against step  114 . The wall thickness of terminal end  120  may be selected so that internal bore  122  of concentrate tubing coupling  100  is slightly smaller than the diameter of bore region  114   a . In this manner, terminal end  120  partially occludes bore region  114   a  whereby flanged end  124  of plug member  126  may be engaged by concentrate tubing coupling  100  as tubing nut  94  is threaded onto fitment housing  66 . Bore region  114   a  may be proportioned to receive flanged end  124  while step  116  has a smaller diameter than flanged end  124  whereby flanged end  124  is precluded from entering bore region  116   a . Plug member  126  may further include a body portion  128  dimensioned to pass through and extend within bore regions  116   a ,  118   a  before terminating at a second end  130 . Second end  130  of plug member  126  may include an O-ring seal  132  having an external diameter greater that the diameter of bore region  118   a . In one aspect of the invention, body portion  128  may be comprised of a plurality of spaced-apart spindles  134  configured to define open slots  136  therebetween so as to promote fluid travel through plug member  126 , as will be discussed in greater detail below. 
     Plug member  126  may translate along longitudinal axis L of fitment housing  66  so as to selectively plug or unplug bore region  118   a  and control outflow of liquid concentrate from second tank  16  to mixing matrix  38 . To that end, as shown in  FIG. 7 , tubing nut  94  may be threadably coupled to fitment housing  66  to thereby secure concentrate tubing coupling  100  therein. Terminal end  120  of concentrate tubing coupling  100  engages flanged end  124  of plug member  126  so as to direct second end  130  a spaced distance from bore region  118   a . In this position, fluid may flow from second tank  16  through tank tubing coupling  72 , fitment housing  66  and the concentrate tubing coupling before passing to mixing manifold  38 . 
     Fitment housing  66  may further include a biasing member, such as compression spring  138 , configured to engage flanged end  124  at a first end  140  and step  118  at second end  142 . In this manner, threading of tubing nut  94  and concentrate tubing coupling  100  may compress spring  138  to thereby cause potential energy to be stored within spring  138 . Unthreading of tubing nut  94  and removal of concentrate tubing coupling  100  from fitment housing  66  enables spring  138  to release the stored potential energy so as to cause plug member  126  to translate along longitudinal axis L generally in the direction generally indicated by arrow  144 . Plug member  126  will continue to translate until O-ring  132  engages surface  146  of fitment housing  66  whereby O-ring  132  and second end  130  of plug member  126  occlude bore region  118   a . In this manner, fluid concentrate may no longer flow into concentrate tubing coupling  100 . As a result, second tank  16  may be rendered substantially leak proof. Second tank  16  may then be removed from mounting bracket  14  as described above and stored with minimal to no loss of liquid concentrate. 
     In accordance with an aspect of the invention, following removal of second tank  16  as described above, a replacement second tank (not shown) may be mounted to mounting bracket  14 . Tubing nut  94  and concentrate tubing coupling  100  may then be threaded onto a fitment housing (similar to fitment housing  66 ) on the replacement second tank as described above. As a result, the plug member within the fitment housing may be opened so as to allow transfer of the alternative liquid concentrate within the replacement second tank to mixing manifold  38  as described above. In a further aspect of the invention, a replacement second tank may be filled with water so as to enable flushing of the system between chemicals that are to be sprayed, thereby reducing cross-contamination or misapplication of the chemicals. Thus, sprayer system  10  may be configured to selectively spray any number of various liquid concentrates requiring only the removal and replacement of selected second tanks and remounting of tubing nut  94  and concentrate tubing coupling  100 . Respective second tanks may be stored with little to no threat of leakage of respective liquid concentrates contained therein, thereby reducing waste of the concentrates. Moreover, user exposure to a concentrate is minimized as the second tank does not need to be emptied, washed and refilled every time a new liquid concentrate desired to be sprayed. 
     Turning now to  FIGS. 9-13 , various views of mixing manifold  38  are shown. As can be seen, housing  58  of mixing manifold  38  may be generally comprised of upper  148  and lower  150  housing subunits. Manifold support member  152  may be interposed between subunits  148 ,  150 . To that end, the interior corners of lower housing subunit  150  may include nodules  154  dimensioned such that respective feet  156  on manifold support member  152  seat upon respective nodules  154 . Upper housing subunit  148  may include respective lobes  158  dimensioned to receive a respective foot  156  therein. Each lobe  158  may also include a notch  160  for permitting passage therethrough of a respective leg  162  on manifold support member  152 . In this manner, manifold support member  152  may be securely seated within manifold housing  58  and be constrained so as to prevent lateral and torsional movement of manifold support member  152 . As described above, manifold support member  152  includes second inlet  54  configured to receive fitment  62 . Manifold support member  152  may further include a spring well  164  dimensioned to receive a stop spring  166 , as will discussed in greater detail below. 
     Mixing manifold  38  may further include disc  168  rotatably mounted atop manifold support member  152  whereby center hole  170  defined by disc  168  receives post  172  formed on manifold support member  152 . Disc  168  may then be capped by upper housing subunit  148  wherein upper housing subunit  148  includes one or more openings  174  therethrough such that a portion of the outer circumference of disc  168  may be engaged by a user so as to selectively rotate disc  168  about post  172 . With additional reference to  FIG. 14 , disc  168  may further define an outer annular series of spaced-apart through-holes, such as flow metering holes  176   a - 176   h . Each of flow metering holes  176   a - 176   h  may have a slightly larger diameter than the immediately preceding flow metering hole. In operation one of holes  176   a - 176   h  is aligned with internal bore  178  defined by fitment  62 . Fitment spring  63  may urge fitment  62  against disc  168  so as to create and maintain a substantially fluid-tight seal between fitment  62  and disc  168 . In this manner, a user may selectively control the volume of liquid concentrate that may pass through disc  168 , as will be discussed in greater detail below. 
     Disc  168  may also further define an inner annular series of spaced apart through-holes, such as chamfered spring stop holes  180   a - 180   h . Each respective spring stop hole  180   a - 180   h  is configured to align radially with its respective flow metering hole  176   a - 176   h . In operation, a selected one of holes  180   a - 180   h  is aligned with spring well  164  whereby a positive stop member, such as ball bearing  182 , seats within a portion of the selected spring stop hole  180   a - 180   h  through urging of stop spring  166  resident within spring well  164 . In this manner, a user may receive feedback indicating proper alignment of the selected flow metering hole  176   a - 176   h  upon seating of ball bearing  182 . To change the amount of liquid concentrate added to the diluent stream, a user may rotate disc  168  whereby disc  168  may apply downward force against ball bearing  182  so as to compress stop spring  166  within spring well  164 . Disc  168  may then be further rotated until the desired flow metering hole  176   a - 176   h  is aligned with internal bore  178  of fitment  62  such that ball bearing  182  seats within the desired spring stop hole  180   a - 180   h . As most clearly shown in  FIG. 14 , disc  168  may also include respective indicia  184   a - 184   h  proximate a respective flow metering hole  176   a - 176   h . Indicia  184   a - 184   h  may correlate with the respective diameter of respective flow metering holes  176   a - 176   h  so as to provide visual indication to the user as to which of the respective flow metering holes  176   a - 176   h  is currently aligned with internal bore  178  of fitment  62 . 
     As seen most clearly in  FIG. 13 , mixing manifold  38  may include a fluid channel  186  wherein a first end  188  of fluid channel  186  may define female threads  190  configured to matingly receive corresponding male threads  192  defined by manifold terminus  194  of first inlet fitting  48 . The opposing second end  196  of fluid channel  186  may similarly define female threads  198  configured to matingly receive corresponding male threads  200  on manifold terminus  202  of manifold outlet fitting  204 . A flow plug  206  may be interposed within fluid channel  186  adjacent the internal extent of female threads  190 . Fluid channel  186  may further define a step  208  so as to provide a positive stop to insertion of flow plug  206  in the direction generally indicated by arrow  210 . In this manner, bore  212  of first inlet fitting  48  may align with the longitudinal axis P of longitudinal bore  214  of flow plug  206  whereby a constant volume of diluent may be received from first tank  12  after flowing through first inlet fitting  48  into flow plug  206 . 
     As further seen in  FIG. 13 , flow plug  206  may further include a radially extending bore  216  which may be configured to fluidly align with one of flow metering holes  176   a - 176   h  and internal bore  178  of fitment  62 . In this manner, a user selected volume of liquid concentrate may be received from second tank  16 , wherein the selected volume of liquid concentrate is then mixed with, and diluted by, the constant volume of diluent being received through first inlet  48  as described above. Flow plug  206  may also define an annular groove  218  configured to define a fluid tight channel with internal wall surface  220  of mixing manifold  38 . Annular groove  218  coincides with radially extending bore  216  such that fluid concentrate may still pass through radially extending bore  216  into longitudinal bore  214  should radially extending bore  216  be misaligned with one of flow metering holes  176   a - 176   h  and internal bore  178 . Fluid channel  186  may further define a mixing chamber portion  222  which may further promote mixing of the diluent and fluid concentrate prior to outputting the mixed fluid through manifold outlet fitting  204 . 
     With reference to  FIGS. 3 and 4 , manifold outlet tubing (not shown) may fluidly couple manifold outlet fitting  204  with positive displacement pump suction port  224 . In this manner, upon a suction stroke of positive displacement pump  42 , mixed fluid is drawn into pump  42  from mixing manifold  38 . As described above, the mixed fluid is comprised of a constant volume of diluent into which is charged a user-selected volume of liquid concentrate. Thus, on a pressure stroke of pump  42 , the mixed fluid is forced out of pressure port  226  of positive displacement pump  42 . Pressure port  226  may be fluidly coupled to a spray device, such as a spray wand or boom sprayer (not shown). To prevent backflow of mixed fluid through first inlet fitting  48  into first tank  12 , first inlet fitting  48  may include a check valve  228  (see  FIG. 13 ). In this manner, cyclical operation of positive displacement pump  42  will alternately draw mixed fluid from mixing manifold  38  and discharge this mixed fluid through an attached sprayer whereby the concentration of the fluid concentrate dilution is selected, and easily modified by, the user through setting of disc  168 . In should be understood by those skilled in the art that positive displacement pump  42  may be powered by any suitable power source, such as a dedicated battery or through wiring pump  42  to the battery of the vehicle (e.g., ATV or golf cart). 
     Turning now to  FIG. 15 , a sprayer system  10 ′ may be configured to operate as a variable pressure sprayer. Sprayer system  10 ′ may include first tank  12  and second tank  16  each fluidly coupled to mixing manifold  38  as described above with regard to sprayer system  10 . Check valve  228  may be interposed between mixing manifold  38  and first tank  12  to prevent backflow of mixed fluid into first tank  12 , also as described above. Mixed fluid may be drawn from mixing manifold  38  through operation of positive displacement pump  42  whereby the mixed fluid is output through pressure port  226 . The mixed fluid may then be selectively delivered to a spray nozzle  230  (such as a handheld sprayer) or to a boom  232  upon which are mounted a plurality of boom nozzles  234 . 
     In accordance with one aspect of the invention, flow to spray nozzle  230  or boom  232  may be selectively controlled by a selector valve  236 . Flow control at each boom nozzle  234  may also be further controlled by respective ball valve  238 . Spray nozzle  230  may also include a pressure reducing valve  240  which is metered to control the fluid pressure of the mixed fluid entering spray nozzle  230  so as to minimize or prevent damage to spray nozzle  230 . 
     Positive displacement pump  42  may include a pressure by-pass recirculation loop  242  fluidly coupling pressure port  226  with suction port  224 . Pressure by-pass recirculation loop  242  may operate to decrease the fluid pressure of the mixed fluid being delivered to spray nozzle  230  while also maintaining segregation of the mixed fluid from either first tank  12  or second tank  16 . Pressure by-pass recirculation loop  242  may be either internal to positive displacement pump  42  of may be en external pressure by-pass loop around positive displacement pump  42 . 
     Referring now to  FIGS. 16 through 24 , in accordance with a further aspect of the present invention, a backpack sprayer system  300  may generally comprise a first tank  312  and second tank  316  mounted onto a mounting bracket  314 . Backpack sprayer system  300  may further include a mixing manifold  38  and positive displacement pump  42 , such as those described above with regard to spray system  10 . 
     As shown most clearly in  FIGS. 16-19, 22, 24 , mounting bracket  314  include a mounting plate  318  and extended upper sidewall portion  320 . In this manner, mounting bracket  314  may receive first tank  312  within upper sidewall portion  320  whereby bottom wall  312   a  of first tank  312  sits upon mounting plate  318 . As further shown in  FIGS. 22 and 24 , second tank  316  may be defined by a sidewall  322  and bottom wall  324 . In one aspect, second tank  316  may reside within, and be fixedly secured to, first tank  312 , although it should be noted that in other embodiments, second tank  316  may be separable from first tank  312 . Rear wall  312   b  of first tank  312  and rear wall  314   b  of mounting bracket  314  may have a curved profile so as to more ergonomically rest against a user&#39;s back during use. To secure backpack sprayer system  310  to the user&#39;s back, sides  314   c ,  314   d  of mounting bracket  314  may include a strap clip  326 . In this manner, first ends of respective straps (not shown) may be secured to a respective strap clip  326 . The opposing second end of each strap may then be secured to tank clip  328  mounted on top wall  312   c  of first tank  312 . The straps may be worn over the user&#39;s shoulders so as to hold backpack sprayer system  310  against the back of the user. 
     With continued reference to  FIGS. 16-19, 22, 24 , and with additional reference to  FIG. 20 , mounting plate  318  may define a pair of orifices  330 ,  332  therein. Orifice  330  may be proportioned to allow passage of first tank fitting  334  therethrough, while orifice  332  is proportioned to allow passage of second tank fitting  336  therethrough. A mixing manifold  38  may be mounted to mounting bracket  314  and include a first inlet fitting  48  and second inlet fitting  54 . Diluent tubing  338  may fluidly couple first tank fitting  334  with first inlet fitting  48  while concentrate tubing  340  may fluidly couple second tank fitting  336  with second inlet fitting  54 . In this manner, mixing manifold  38  may receive a fixed amount of diluent from the first tank and an adjustable amount of liquid concentrate from the second tank. The fixed amount of diluent and adjustable amount of concentrate are then combined within mixing manifold  38  to form a mixed solution which is discharge from mixing manifold  38  through a mixed solution outlet, such as manifold outlet fitting  204  ( FIG. 24 ). 
     As described above, manifold outlet tubing, such as tubing  342 , may fluidly couple manifold outlet fitting  204  with positive displacement pump suction port  224 . In this manner, upon a suction stroke of positive displacement pump  42 , mixed fluid is drawn into pump  42  from mixing manifold  38 . The mixed fluid is comprised of a constant volume of diluent into which is charged a user-selected volume of liquid concentrate. Thus, on a pressure stroke of pump  42 , the mixed fluid is forced out of pressure port  226  of positive displacement pump  42  ( FIG. 21 ). Pressure port  226  may be fluidly coupled to a spray device, such as a spray wand (not shown), accessible through hole  344  defined in front wall  314   a  of mounting bracket  314  ( FIGS. 16, 18 and 19 ) 
     As described above with reference to  FIGS. 9-13 , housing  58  of mixing manifold  38  may be generally comprised of upper  148  and lower  150  housing subunits. Manifold support member  152  may be interposed between subunits  148 ,  150 . To that end, the interior corners of lower housing subunit  150  may include nodules  154  dimensioned such that respective feet  156  on manifold support member  152  seat upon respective nodules  154 . Upper housing subunit  148  may include respective lobes  158  dimensioned to receive a respective foot  156  therein. Each lobe  158  may also include a notch  160  for permitting passage therethrough of a respective leg  162  on manifold support member  152 . In this manner, manifold support member  152  may be securely seated within manifold housing  58  and be constrained so as to prevent lateral and torsional movement of manifold support member  152 . As described above, manifold support member  152  includes second inlet  54  configured to receive fitment  62 . Manifold support member  152  may further include a spring well  164  dimensioned to receive a stop spring  166 , as will discussed in greater detail below. 
     Mixing manifold  38  may further include disc  168  rotatably mounted atop manifold support member  152  whereby center hole  170  defined by disc  168  receives post  172  formed on manifold support member  152 . Disc  168  may then be capped by upper housing subunit  148  wherein upper housing subunit  148  includes one or more openings  174  therethrough such that a portion of the outer circumference of disc  168  may be engaged by a user so as to selectively rotate disc  168  about post  172 . With additional reference to  FIG. 14 , disc  168  may further define an outer annular series of spaced-apart through-holes, such as flow metering holes  176   a - 176   h . Each of flow metering holes  176   a - 176   h  may have a slightly larger diameter than the immediately preceding flow metering hole. In operation one of holes  176   a - 176   h  is aligned with internal bore  178  defined by fitment  62 . Fitment spring  63  may urge fitment  62  against disc  168  so as to create and maintain a substantially fluid-tight seal between fitment  62  and disc  168 . In this manner, a user may selectively control the volume of liquid concentrate that may pass through disc  168 , as will be discussed in greater detail below. 
     Disc  168  may also further define an inner annular series of spaced apart through-holes, such as chamfered spring stop holes  180   a - 180   h . Each respective spring stop hole  180   a - 180   h  is configured to align radially with its respective flow metering hole  176   a - 176   h . In operation, a selected one of holes  180   a - 180   h  is aligned with spring well  164  whereby a positive stop member, such as ball bearing  182 , seats within a portion of the selected spring stop hole  180   a - 180   h  through urging of stop spring  166  resident within spring well  164 . In this manner, a user may receive feedback indicating proper alignment of the selected flow metering hole  176   a - 176   h  upon seating of ball bearing  182 . To change the amount of liquid concentrate added to the diluent stream, a user may rotate disc  168  whereby disc  168  may apply downward force against ball bearing  182  so as to compress stop spring  166  within spring well  164 . Disc  168  may then be further rotated until the desired flow metering hole  176   a - 176   h  is aligned with internal bore  178  of fitment  62  such that ball bearing  182  seats within the desired spring stop hole  180   a - 180   h . As most clearly shown in  FIG. 14 , disc  168  may also include respective indicia  184   a - 184   h  proximate a respective flow metering hole  176   a - 176   h . Indicia  184   a - 184   h  may correlate with the respective diameter of respective flow metering holes  176   a - 176   h  so as to provide visual indication to the user as to which of the respective flow metering holes  176   a - 176   h  is currently aligned with internal bore  178  of fitment  62 . With reference to  FIG. 17 , a portion of disc  168  may extend outwardly through sidewall  314   d  such that a user may conveniently adjust the dilution factor of the fluid concentrate comprising the mixed fluid. 
     As seen most clearly in  FIG. 13 , mixing manifold  38  may include a fluid channel  186  wherein a first end  188  of fluid channel  186  may define female threads  190  configured to matingly receive corresponding male threads  192  defined by manifold terminus  194  of first inlet fitting  48 . The opposing second end  196  of fluid channel  186  may similarly define female threads  198  configured to matingly receive corresponding male threads  200  on manifold terminus  202  of manifold outlet fitting  204 . A flow plug  206  may be interposed within fluid channel  186  adjacent the internal extent of female threads  190 . Fluid channel  186  may further define a step  208  so as to provide a positive stop to insertion of flow plug  206  in the direction generally indicated by arrow  210 . In this manner, bore  212  of first inlet fitting  48  may align with the longitudinal axis P of longitudinal bore  214  of flow plug  206  whereby a constant volume of diluent may be received from first tank  312  after flowing through first inlet fitting  48  into flow plug  206 . 
     As further seen in  FIG. 13 , flow plug  206  may further include a radially extending bore  216  which may be configured to fluidly align with one of flow metering holes  176   a - 176   h  and internal bore  178  of fitment  62 . In this manner, a user selected volume of liquid concentrate may be received from second tank  316 , wherein the selected volume of liquid concentrate is then mixed with, and diluted by, the constant volume of diluent being received through first inlet  48  as described above. Flow plug  206  may also define an annular groove  218  configured to define a fluid tight channel with internal wall surface  220  of mixing manifold  38 . Annular groove  218  coincides with radially extending bore  216  such that fluid concentrate may still pass through radially extending bore  216  into longitudinal bore  214  should radially extending bore  216  be misaligned with one of flow metering holes  176   a - 176   h  and internal bore  178 . Fluid channel  186  may further define a mixing chamber portion  222  which may further promote mixing of the diluent and fluid concentrate prior to outputting the mixed fluid through manifold outlet fitting  204 . 
     With reference to  FIGS. 22 and 24 , first tank  312  may be filled with diluent through tank opening  346  defined by a threaded mouth portion  348 . A cap  350  may be removably threaded onto mouth portion  348  so as to seal first tank  312 . To prevent clogging of downstream plumbing components, mouth portion  348  may further receive filter element  352  therein. When filling first tank  312 , the diluent passes through filter element  352  whereby particulate matter larger than the pore size of the filter element will be strained out of the fluid. Accordingly, the pore size of filter element  352  should be selected so as to be smaller than the internal diameter of the smallest diameter downstream component. Similarly, second tank  316  is configured to receive fluid concentrate through mouth portion  354  which is capped by a cap  356 . Cap  356  may also carry a fluid level gauge  358 , such as but not limited to a float gauge, an ultrasonic level gauge and the like. Cap  356  may also include a dial or meter  360  coupled to gauge  358  so as to provide a visual indication of the fluid volume of the fluid concentrate within second tank  316 . 
     As shown in  FIGS. 16, 18 and 24 , backpack sprayer system  300  may include a battery  362  configured to provide electrical power to positive displacement pump  42 . To that end, front wall  314   a  of mounting bracket  314  may include a battery receiving fixture  364  configured to removably secure battery  362  within mounting bracket  314 . In accordance with an aspect of the present invention, battery  362  is a rechargeable, long-life battery, such as a lithium ion battery. Mounting bracket  314  may also include a control unit  366  mounted thereon. Control unit  366  may comprise a printed circuit board (PCB)  368  and control panel interface  370 . PCB  368  may include a processor and memory configured to perform one or more functions including power on/power off, regulating power to the positive displacement pump so as to vary output pressure of the mixed solution, monitoring and displaying a battery charge level, and indicating pacing, as described more fully below. Control panel interface  370  includes one or more control buttons whereby a user controls the processor functions of PCB  368 . 
     As discussed below, control unit  366  may promote smart operation of backpack sprayer system  300 . With reference to  FIG. 25 , control panel interface  370  may generally include a visual display via output pressure LEDS  370   a , battery charge level LEDS  370   b , and a warning indicator LED  370   c  and associated buzzer or other audio warning device. Functionality of the display, PCB  368  and mechanical components (i.e., positive displacement pump  42 ) may be selectively controlled through one or more buttons on control panel interface  370 , such as and without limitation, power/control button  372  and pace button  374 . 
     By way of example and without limitation thereto, control unit  366  may enable power on (pressing power/control button  372 ) and power off (pressing and holding pace button  374  for a predetermined period of time. Pressure status may be generally indicated by output pressure LEDS  370   a . For instance, the greater the number of LEDS  370   a  lit, the higher the output pressure. Output pressure may be increased by pressing power/control button  372 . When at maximum pressure, another press of power/control button  372  will cycle back to the minimum pressure setting. Control unit  366  may also permit setting of a set pressure lock whereby pressing of power/control button  372  will not cycle the output pressure setting. By way of example, to set the pressure lock, PCB  368  may include logic whereby power/control button  372  is held for a predetermined period of time (e.g., 10 seconds) at which point the current pressure setting is locked, even after backpack sprayer system  300  has turned off or battery  362  has been removed and replaced. To disable the pressure lock, PCB  368  may include logic, such as, for example, pressing power/control button  372  three times followed by pressing pace button  374  within 3 seconds. 
     Similarly, pace button  374  may allow cycling of pacing whereby control unit  366  will emit a beep or other audible signal such that a user may control his or her walking pace so as to apply a more consistent spray. Control unit  366  may also keep track of and indicate total labor time of backpack sprayer system  300 . One exemplary control algorithm to display total labor time may include pressing power/control button  372  followed by pressing and holding power/control button  372  and pace button  374  simultaneously for a predetermine period of time. Output pressure LEDS  370   a  may then blink to indicate a time range, i.e., 0 LEDs indicates less than 300 hours, 1 LED indicates between 300 and 700 hours, 2 LEDS indicates between 700 and 1000 hours, etc. Warning indicator LED  370   c  and associated buzzer may be used to indicate a problem associated with the battery, e.g., that the battery has low charge or is experiencing an overvoltage. 
     Turning now to  FIGS. 26 through 28 , in accordance with another aspect of the present invention, a backpack sprayer system  400  is shown. Backpack sprayer system  400  is similar to backpack sprayer system  300  described above and generally includes a first tank  412  and second tank  416  mounted onto a mounting bracket  414 . Backpack sprayer system  400  may further include a mixing manifold  38  and positive displacement pump  42 , such as those described above with regard to spray system  10  and sprayer system  300 . Mounting bracket  414  has been modified to include an orifice  417  therethrough for passage of a concentrate fitting  420 , as will be discussed in greater detail below (see  FIGS. 28 and 29 ). All other aspects of mounting bracket  414 , mixing manifold  38 , positive displacement pump  42  and control unit  366  have been previously described with regard to backpack sprayer system  300 . 
     With reference to  FIGS. 27 and 28 , first tank  412  includes a bottom wall  412   c  proportioned to be received within mounting bracket  414 . Rear wall  412   b  of first tank  412  may have a curved profile so as to more ergonomically rest against a user&#39;s back during use, as described above. Front wall  412   d  may define a recess  418  within which at least a portion of rear wall  416   a  and side walls  416   b ,  416   c  of second tank  416  may be received. Front wall  412   d  may also include a nodule  412   d ′ which is configured to seat within a corresponding notch  416   a ′ defined along rear wall  416   a  of second tank  416  when second tank  416  is properly positioned within recess  418  with concentrate fitting  420  passing through orifice  417  in mounting bracket  414 . 
     With reference to  FIG. 30 , mounting bracket  414  may define a pair of orifices  415  ( FIG. 27 ) and  417  therein. Orifice  415  may allow passage of a first tank fitting therethrough, similar to first tank fitting  334  described above. Orifice  417  may allow passage of concentrate fitting  420  therethrough. A mixing manifold  38  may be mounted to mounting bracket  414  and include a first inlet fitting  48  and second inlet fitting  54  as described above. Diluent tubing  442  may fluidly couple the first tank fitting with first inlet fitting  48  while concentrate tubing  444  may fluidly couple concentrate fitting  420  with second inlet fitting  54 . In this manner, mixing manifold  38  may receive a fixed amount of diluent from the first tank and an adjustable amount of liquid concentrate from the second tank. The fixed amount of diluent and adjustable amount of concentrate are then combined within mixing manifold  38  to form a mixed solution which is discharge from mixing manifold  38  through a mixed solution outlet, such as manifold outlet fitting  204 . Note, positive displacement pump  42  has been removed from  FIG. 30  so as to more clearly show the tubing connections. However, when fully assembled, mounting bracket  414  will include a positive displacement pump  42  similar to that shown in  FIG. 21 . 
     To releasably secure second tank  416  within mounting bracket  414  and to first tank  412 , top wall  412   a  of first tank  412  may carry a clamp  422 . In accordance with an aspect of the invention, top wall  412   a  may include a tab  412   a ′ configured to mount clamp  422  to first tank  412 . Clamp  422  may include a clip  424  proportioned to receive tab  412   a ′ therein. Clip  424  may include one or more threaded bores  426  which align with apertures  428  within tab  412   a ′. A threaded fastener (not shown) may then secure clip  424  by passing through bores  426  and aperture  428 . Clamp arm  430  is pivotally mounted to clip  424  via pivot pin  432  at a first end  430   a . In a further aspect of the invention, a second pivot pin  434  and pivot extension  436  may also be included to permit greater ease in releasing clamp arm  430 , as will be discussed below. Second end  430   b  of clamp arm  430  is configured to releasably couple with second tank  416 , such as through releasably engaging projection  438  extending upwardly from rear wall  416   a  of second tank  416  (see  FIG. 29 ). Thus, when in a clamped position, as shown in  FIG. 29 , second end  430   b  engages projection  438  to pull second tank  416  into recess  418  so as to secure second tank  416  against first tank  412  and within mounting bracket  414  (see  FIG. 1 ). Lifting second end  430   b  upwardly, as generally indicated by arrow  440 , will disengage second end  430   b  from projection  438  through pivoting of clamp  430  about pivot pin  432  (and optional second pivot pin  434 ). Second tank  416  may then be lifted from mounting bracket  414  and decoupled from first tank  412 . 
     In accordance with an aspect of the present invention, a valve  446  ( FIG. 28 ) within second tank  416  may selectively seal second tank  416  so as to prevent unwanted leaking of concentrate fluid from second tank  416  when not properly mounted within mounting bracket  414 . By way of example and without limitation thereto, valve  446  may comprise a poppet valve extending within concentrate fitting  420 . The poppet valve may be actuated in a first direction when second tank  416  is mounted into mounting bracket  414  so as to fluidly couple second tank  416  with concentrate tubing  444  and mixing manifold  38 . The poppet valve may then be actuated in an opposing second direction when second tank  416  is removed from mounting bracket  414 . An alternative second tank  416  may then be coupled and clamped to mounting bracket  414  and first tank  412  as described above. In this manner, any number of second tanks  416  may be quickly and easily swapped into and out of backpack sprayer system  400  without contaminating the diluent (e.g., water) within first tank  412 . 
     As shown in  FIGS. 26, 27 and 30 , backpack sprayer system  400  may include a battery  362  configured to provide electrical power to positive displacement pump  42  and a control unit  366 . As described above with reference to backpack sprayer system  300 , control unit  366  may comprise a printed circuit board (PCB)  368  and control panel interface  370  (see  FIGS. 24 and 25 ). PCB  368  may include a processor and memory configured to perform one or more functions including power on/power off, regulating power to the positive displacement pump so as to vary output pressure of the mixed solution, monitoring and displaying a battery charge level, and indicating pacing, as described above. Control panel interface  370  includes one or more control buttons whereby a user controls the processor functions of PCB  368  such that, as described above, control unit  366  may promote smart operation of backpack sprayer system  400 . 
     The foregoing description of the preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above teachings. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.