Liquid dispensing gun
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of devices for dispensing a predetermined quantity of liquid from a pressurized source in response to each actuation of the device. It finds particular, but not exclusive, utility for dispensing viscous liquids such as ketchup. The device lends itself to advantageous use in fast food operations where careful quantity control of the dispensed liquid is important to the quality of the product and the economics of the operation. 
     A wide variety of devices for dispensing measured quanities of liquid have been devised heretofore. Such prior devices have numerous shortcomings, including complexity, expense, difficulty in dismantling for cleaning purposes, imprecise measuring of liquid dispensed, or difficulty in handling liquid from a pressurized source. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a gun for repeatedly and reliably dispensing precisely metered quantities of liquid from a pressurized source in a high production operation. 
     Another object of the invention is to provide a dispensing gun of the type set forth above adapted to be manually actuated with precision by application of fingertip forces. A related object is to provide a dispensing gun of the foregoing nature which is adapted to be operated under power as well as manual means. 
     A further object is to provide a dispensing gun of the above type which is of simple, compact construction and capable of quick disassembly for cleaning and quick reassembly after cleaning. 
     Another object of the invention is to provide a dispensing gun of the above character capable of handling pressurized liquid without leakage. 
     The foregoing objectives are accomplished by the present invention through a remarkably simple and efficient dispensing gun adapted to operate from a pressurized source of viscous liquid. The gun comprises a hollow body having a valve chamber with an inlet and an outlet port and a metering chamber connected to the valve chamber by a control orifice; and axially slidable valve spool in the valve chamber resiliently biased into engagement with the control orifice; a metering piston in the metering cylinder resiliently biased toward the control orifice; and a trigger operated actuating plunger adapted to shift the valve spool between a first position for loading the metering chamber with pressurized liquid and overcoming the metering piston biasing means while the outlet port is blocked, and a second position for discharging a metered quantity of liquid from the metering chamber through the control orifice while the outlet port is open and the inlet port is blocked. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of an illustrative liquid dispensing gun exemplifying the present invention. 
     FIG. 2 is an enlarged fragmentary sectional view taken axially through the body of the dispensing gun shown in FIG. 1 with the parts in the intake position. 
     FIG. 3 is an enlarged fragmentary sectional view similar to FIG. 2 but with the dispensing gun in process of discharging liquid from the metering cylinder. 
     FIG. 4 is an enlarged fragmentary sectional view similar to FIG. 2 but with the metering cylinder in the fully discharged condition. 
    
    
     While the invention is susceptible of various modifications and alternative constructions, a certain illustrative embodiment has been shown in the drawings and will be described below in considerable detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the scope of the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring more specifically to FIGS. 1-4, the present invention is there exemplified in a dispensing gun 10 adapted when actuated by manual or power means to dispense precisely metered quantitites of liquid. The gun 10 comprises a hollow body 11 connected to a pressurized supply line 12 which in this instance contains ketchup. The supply line 12 passes through a handle 14 attached to the body and terminates in a supply line fitting 15 threadedly connected to the body. An acutating trigger 16 is pivotally attached to a support bracket 18 fixed to one end of the body. Fluid is discharged from an outlet nozzle 19 threadedly attached to the body by nozzle fitting 20. Each time the trigger 16 is squeezed toward the handle 14, a precisely metered quantity of ketchup is discharged from the gun 10. Upon release of the trigger, the gun promptly reloads for the next discharge. 
     In order to provide for the intake and discharge of liquid to and from the dispensing gun 10, the body 11 is formed with a valve chamber 21 and a metering chamber 22. The chambers 21 and 22 are axially aligned and connected by a control orifice 24. Adjacent the end of the body remote from the control orifice, the valve chamber is formed with an inlet port 25 which communicates with the supply line fitting 15 and the pressurized liquid supply. Between the inlet port 25 and the control orifice 24, the valve chamber is formed with an outlet port 26 communicating with nozzle 19 and its fitting 20. 
     In accordance with the invention, a resiliently biased valve spool 28 is mounted for axial sliding movement within the valve chamber to regulate the flow of liquid from the inlet port into the metering chamber, and from the metering chamber to the outlet port. The valve spool 28 has a first operative position establishing communication between the inlet port 25 and the metering chamber 22 while blocking the outlet port 26. The valve spool has a second operative position establishing communication between the metering chamber 22 and the outlet port 26 while blocking the inlet port 25. 
     Referring in greater detail to the valve spool 28, it will be noted that the latter is formed intermediate its ends with a pair of axially spaced lands 29, 30 each of somewhat larger diameter than the remainder of the spool. Each land in this case has an annular groove which houses a respective one of O-rings 31, 32 formed of resilient sealing material. The land 29 and its O-ring 31 serve as a movable seal isolating the inlet port 25 from the outlet port 26. The land 30 and its O-ring 32 serve as a movable seal preventing leakage of pressurized liquid from the inlet port 25 to the end of the valve chamber remote from the control orifice 24. The end of the valve spool 28 facing the metering chamber 22 is formed with a taper 34 adapted to sealingly engage a mating seat 35 on the control orifice 24. At its opposite end, the valve spool has an axial stem 36 of reduced diameter which is surrounded by a resilient biasing means in the form of a spiral spring 38. The spring 38 bears against a cap 39 threaded on one end of the body 11 and an annular shoulder on the valve spool surrounding the stem 36. By reason of this construction, the valve spool 28 is biased into engagement with the control orifice 24. 
     Provision is made for injecting liquid from the pressurized source into the metering chamber 22 via the valve spool 28. The spool 28 is thus formed with an axial passage 40 open at the downstream end which faces the metering chamber and connected at its upstream end with a radial passage 41 which communicates directly with the inlet port 25. When the trigger 16 is in its non-actuated position, the downstream end of the axial passage 40 is open and pressurized liquid flows from the supply line 12 through fitting 15, inlet port 25, passages 41, 40 and into the metering chamber 22 (FIG. 2). 
     For the purpose of metering the liquid injected into the metering chamber 22 by the valve spool 28, a metering piston 42 is slidably housed within the chamber 22. The piston 42 is of cup-shaped form, defining an annular recess 44 in the face remote from the control orifice 24. The recess 44 houses a resilient biasing means in the form of a spiral spring 45. The latter is interposed between the bottom end of the recess 44 and a cap 46 fixed to the end of the body 11 adjacent to the trigger 16. The outer periphery of the piston 42 has a groove accommodating an O-ring 48 which defines a sliding seal with the wall of the metering chamber 22. The characteristic of the spring 45 of the metering piston is such that it is adapted to yield against the force of an incoming charge of liquid from the valve spool passage 40. When the incoming liquid charge is cut off and the metering chamber is connected to the outlet, the spring 45 is adapted to drive the metering piston 42 toward the control orifice and against the opposed end wall of the metering chamber to expel the charge of liquid via the outlet port 26. 
     The volume of liquid delivered by the gun 10 may be selectively varied by means of an adjustment stop 49 adapted to alter the stroke of the metering piston within close tolerances. In the present instance, the stop 49 comprises a screw mounted in a tapped hole in the end wall of the cap 46 and an associated lock nut. The stop 49 is positioned so as to engage the annular end face of the piston surrounding the biasing spring 45 and thereby regulate the piston stroke. 
     As indicated earlier herein, the gun 10 is actuated by means of trigger 16 to discharge a precisely measured quantity of liquid from the nozzle 19. The gun thus includes an actuating plunger 50 constrained for axial sliding movement within the body 11 and operatively connected to an intermediate portion of the trigger 16 spaced radially from its pivot 51 on bracket 18. The main body portion of the plunger 50 has a length equal to or slightly shorter than the length of the metering chamber. A portion of reduced diameter, defining a shoulder 52 with the main body portion, is slidably mounted relative to an aperture in the end wall of cap 46. The reduced diameter portion connects the actuating plunger 50 to the trigger 16 by means of an appropriate coupling 54 engageable by a pin 55 on the trigger. 
     In order to accommodate the straight line or axial motion of the plunger 50 to the arcuate motion of the trigger 16 about its pivot 51, the coupling 54 is fashioned in a general U-shape, defining two spaced apart slide surfaces 56, 58. Accordingly, when the trigger is actuated the radial thrust of the trigger pin 55 will be accompanied by relative linear movement of the pin along one or the other of slide surfaces 56, 58 depending upon the direction in which the trigger is moved about its own pivot 51. 
     To receive the main portion of the actuating plunger 50, the metering piston 42 has a central bore 59 with a sliding seal in the form of an O-ring 60. The projecting inner end of the actuating plunger 50 has a chamfer 61 adapted to enter into sealing engagement with a seat 62 at the mouth of the axial bore 40 of the valve spool. 
     To maintain the orientation of the trigger 16 parallel to the handle 14, appropriate registration means are provided between the spring cap 46 and the body 11 (FIGS. 2-4). In this instance, the body is formed with a shoulder 64 between the skirt 65 defining the outer end portion of the metering chamber and the outer end of the threads surrounding the metering chamber. At least one pair of diametrically opposed flats 66 is formed in the shoulder 64. The spring cover or cap 46 is fashioned with a corresponding pair of diametrically opposed, axially extending, segmental lugs 68. When the cap 46 is telescoped over the metering chamber skirt 65, the lugs 68 on the cap register with the flats 66 in the shoulder 64, thereby orienting the cap 46 and thus the trigger 16 with respect to the body and the handle 14. Tightening of the clamp ring 69 thereby retains the trigger 16 in properly oriented position. 
     The operation of the gun 10 will become more apparent in light of the foregoing description. Starting with the trigger 16 in the rest position shown in FIGS. 1 and 2, the tapered end 34 of the valve spool 28 is seated in the control orifice 24 and the actuating plunger 50 is in its retracted position. Under this condition, shown in FIG. 2, pressurized liquid from the supply line 12 enters the inlet port and passages 41, 40 of the valve spool, filling the void space in the metering chamber between the face of the metering pistion 42 and the end wall of the metering chamber surrounding the control orifice. At this time, the outlet port 26 is completely blocked by the valve spool 28. Upon squeezing the trigger 16 against the handle 14, the actuating plunger 50 moves axially from the position shown in FIG. 2 to that shown in FIG. 3. As an incident to such movement, the projecting end of the actuating plunger engages the seat 62 at the end of the valve spool passage 40, precluding entry of additional liquid through the inlet port. At the same time, such action also forces the valve spool 28 to the right, compressing its biasing spring 38 and establishing communication with the outlet port 26 via the control orifice 24. This relieves the back pressure on the liquid within the metering chamber and the metering piston 42 thus moves toward the control orifice under the force of its biasing spring 45. Such motion continues, passing from the condition illustrated in FIG. 3 to that shown in FIG. 4 where the metering piston 42 has emptied the metering chamber of its precise quanity of liquid and has brought its face into abutment with the inner end wall of the metering chamber. 
     Upon release of the trigger 16 following discharge of the metered quantity of liquid, the valve spool 28 and the actuating plunger 50 will be driven in unison to the left by the biasing spring 38 until the tapered end 34 of the valve spool engages the mating seat of the control orifice 24, as shown in FIG. 2. Since this cuts off communication with the outlet port, liquid pressure from the supply line bears against the projecting end of the actuating plunger, forcing it to the left until the shoulder 52 at the end of the enlarged portion engages the inner face of the cap 46, also as shown in FIG. 2. This establishes communication of pressurized liquid between the valve spool passage 40 and the metering chamber via the control orifice, forcing the metering piston to the left against the biasing spring and refilling the metering chamber. At that point, the gun is ready for another cycle. 
     Since the embodiment of the present invention described above is utilized in the food industry, sanitation is an important consideration. The construction of the gun 10 lends itself well to quick disassembly for cleaning. The end caps 39, and 46, being threadedly attached to the body 11, may readily be removed. This permits easy removal of the valve spool 28 and its biasing spring. Upon removal of the end cap 46 and disconnection of the pivotal fitting on the actuating plunger from the trigger, the metering piston 42, its biasing spring 45, and the actuating plunger may readily be removed from the metering chamber. The O-ring type liquid seals on the valve spool and metering piston lend themselves to easy removal for cleaning. Following the cleaning operation, the parts of the gun may be quickly and easily reassembled to restore the gun to service.