Abstract:
An apparatus for applying a foamable fluid plastic material including reactant fluids that form a foam when heated and mixed. A reactant fluid dispenser supplies the reactant fluids to a heated applicator gun mixing chamber at a constant flow rate despite any differences in viscosity. A valve needle extends into the mixing chamber and exposes fluid inlet openings when retracted, permitting the reactant fluids to flow into the mixing chamber. When advanced, the needle closes off the fluid inlet openings and dispenses the mixed fluids. A heater prevents the gun from drawing heat energy from initial quantities of the pre-heated reactant fluids which would prevent initial quantities of the fluids from reacting properly. The valve needle is disposed in a sleeve that defines the mixing chamber and is disposed in a sleeve receptacle of the gun. The fluid inlet openings may be disposed through a portion of a wall of the sleeve that includes a flat exterior surface that is disposed against a corresponding flat surface of the sleeve receptacle, the mixing chamber fluid inlets opening through the flat sleeve receptacle surface. A seal may be disposed around each mixing chamber fluid inlet between the respective flat portions of the sleeve and the sleeve receptacle to seal those surfaces against the escape of reactant fluids.

Description:
This application is based on provisional application Ser. No. 60/074,276 filed Feb. 10, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus for dispensing and applying a multi-component foamable fluid plastic material, including polyurethane foams. 
     DESCRIPTION OF THE PRIOR ART 
     Foam application apparatus are commercially available that apply multi-component foamable fluid plastic materials, preferably polyurethanes. The standard reactant fluids comprise a plastic material fluid component and an isocyanate fluid component bearing comparable viscosities and used in comparable ratios. 
     Typically, foam application apparatus include a cylindrical mixing chamber having separate orifi or fluid inlet openings for each reactant component and an axial passage transverse to the direction of the inlet passages for allowing the mixed or reacted fluid to exit the mixing chamber. The mixing chamber is typically mounted in a support body structure. The dimensional tolerance between the mixing chamber and valve body is made sufficiently close so that the reactant fluids cannot flow therebetween. Standard reactant fluids are sufficiently viscous to not normally flow between the mixing chamber and valve body. 
     A cylindrical rod or valve needle having an external diameter nearly the same as the internal diameter of the cylindrical mixing chamber moves forwardly and rearwardly in the mixing chamber. In the forward position, the valve needles close off the fluid inlet openings to prevent any fluid from entering the mixing chamber. In the rearward position, the valve needle is retracted under hydraulic pressure to expose the inlet openings to permit their respective fluids to flow in the mixing chamber and impingement mix therein. When enough reacted fluid has been dispensed, the valve needle moves to its forward position to once again close the inlet passages and prevent reactant fluid flow into and mixing in the mixing chamber. 
     Many apparatus of this type are well known in the art, including U.S. Pat. No. 4,377,256 to Commette, et al., and U.S. Pat. No. 5,339,991 to Synder. One common problem that is disclosed in U.S Pat. No. 5,339,991 is that conventional foam applications commonly seize up after a few thousand shots requiring cleaning of the valve components and mixing chamber before reuse. 
     Another problem associated with the prior art apparatus is that the foam application gun is not heated. This requires that the combination of heat energy dissipated from the heated reactant fluids and the heat given off by the reaction of the reactant fluids in the mixing chamber are used to heat the gun. One drawback with this is that the first several shots exiting the dispensing apparatus are wasted because the apparatus is not at a suitable temperature for carrying out the foaming reaction. Thus, heat is removed from the reactant fluids and the initial reacted fluids exiting the mixing chamber are not at a sufficiently high temperature for proper reaction. 
     Another problem has recently developed with respect to foam application guns. Recently developed chemistry using non-standard reactant fluids may also be used to make the plastic foam. These new reactant fluids use no or low isocyanates as one reactant fluid and a resin component as another reactant fluid. Some of these non-standard reactant fluids are not as viscous as the standard reactant fluids and may tend to seep between the mixing chamber and valve body. Furthermore, the ratios of reactant fluids in this type of system are not necessarily comparable. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     According to the invention, an apparatus is provided for applying a multi-component foamable fluid plastic material, the material including at least two reactant fluids configured to form a foam when heated and mixed. The apparatus includes a heater disposed on and configured to heat a support body structure of an applicator gun. The apparatus also includes a mixing chamber supported in the support body structure and configured to receive pre-heated reactant fluids for mixing through two mixing chamber fluid inlet openings. The mixing chamber comprises an axial passage disposed generally transverse to the fluid inlet openings and configured to allow reactant fluids to exit the mixing chamber through an axial outer end of the axial passage. Two mixing chamber fluid inlets are disposed in the support body structure in fluid communication with the mixing chamber and are configured to direct the respective reactant fluids into the mixing chamber through the respective mixing chamber fluid inlet openings. An elongated valve needle is supported in the mixing chamber for reciprocal longitudinal movement between forward closed and a rearward open positions in the mixing chamber. The valve needle is configured to expose the fluid inlet openings when retracted to the rearward open position to permit the reactant fluids to flow into the mixing chamber from the respective inlet openings and impingement mix therein. The needle is configured to close off the fluid inlet openings and dispense the mixed fluids from the mixing chamber through the axial passage while being advanced to the forward closed position. The heater prevents the support body structure from drawing heat energy from initial quantities of the pre-heated reactant fluids, which would cool the initial quantities of the fluids, preventing them from reacting properly in the mixing chamber. 
     According to another aspect of the invention, the heater includes two heating elements; each element being disposed adjacent one of the mixing chamber fluid inlets. This allows the temperature of portions of the support body structure adjacent the mixing chamber fluid inlets to be controlled separately. 
     According to another aspect of the invention, the apparatus includes a gun temperature feedback control system including a temperature sensor configured to monitor support body structure temperature and a controller configured to control heater temperature based on temperature sensor inputs. The control system may be configured to control the temperatures of the two heating elements separately. 
     According to another aspect of the invention, the valve needle includes a helical groove configured to purge the mixing chamber of unreacted and reacted fluids by scraping the interior surface of the mixing chamber. 
     According to another aspect of the invention, the valve needle includes a pair of annular grooves disposed such that one of the annular grooves is positioned forward of the mixing chamber fluid inlet openings when the valve needle is in the closed position and the second of the annular grooves is positioned rearward of the mixing chamber fluid inlet openings when the valve needle is in the closed position. The annular grooves are configured to prevent reactant fluids from passing the annular grooves by allowing any residual reactant fluid to collect in the annular grooves and react thus creating a seal between the valve needle and an interior wall of the mixing chamber. 
     According to another aspect of the invention, the mixing chamber is defined by a sleeve supported in a sleeve receptacle in the support body structure. The fluid inlet openings are disposed in a wall of the sleeve. The mixing chamber fluid inlets open through respective flat portions of an interior surface of the sleeve receptacle. The fluid inlet openings are disposed in a flat portions of an exterior surface of the sleeve wall. The flat portions are disposed parallel to the respective flat portions of the interior surface of the sleeve receptacle. A seal is disposed around each mixing chamber fluid inlet and between the respective flat portions of the interior surface of the sleeve receptacle and the exterior surface of the sleeve wall to seal the interior surface of the sleeve receptacle to the exterior surface of the sleeve wall so that reactant fluids cannot escape the mixing chamber fluid inlet between those two surfaces. 
     According to another aspect of the invention, the apparatus comprises a mix head supported at an axial outer end of the support body structure. The sleeve receptacle is disposed in the mix head. 
     According to another aspect of the invention, a portion of one or each mixing chamber fluid inlet may be slightly angled to allow the reactant fluid injected from that inlet to disperse more evenly over the reactant fluid stream entering from the other mixing chamber fluid inlet. 
     According to another aspect of the invention, the wall of the sleeve has a generally rectangular cross-sectional shape along a portion of its length where the sleeve engages the mix head in the sleeve receptacle. The interior surface of the sleeve receptacle is rectangular in cross section and is configured to mate in close proximity with the wall of the sleeve. The seal recesses are disposed in respective generally opposing flat sidewalls of the sleeve receptacle and surround the respective mixing chamber fluid inlets. 
     According to another aspect of the invention, a forward seal is disposed between the sleeve and sleeve receptacle forward of the fluid inlet openings and a rearward seal is disposed between the sleeve and sleeve receptacle rearward of the fluid inlet openings. 
     According to another aspect of the invention, the apparatus includes a reactant fluid dispenser connected to the applicator gun and configured to supply at least one of the reactant fluids to the applicator gun mixing chamber through at least one of the mixing chamber fluid inlets at a constant flow rate. This continuously provides the first reactant fluid in proper proportion to a second one of the reactant fluids despite any differences between the two fluids such as viscosity and/or density. 
     According to another aspect of the invention, the reactant fluid dispenser is configured to supply the first and second reactant fluids to the applicator gun mixing chamber through the respective mixing chamber fluid inlets at constant respective flow rates. 
     According to another aspect of the invention, the reactant fluid dispenser includes a first reactant fluid source configured to dispense the first reactant fluid and a second reactant fluid source configured to dispense the second reactant fluid. A first metering unit is connected between and in fluid communication with the first reactant fluid source and the applicator gun and configured to move the first reactant fluid at a constant predetermined flow rate. A second metering unit is connected between and in fluid communication with the second reactant fluid source and the applicator gun and is configured to move the second reactant fluid at a constant predetermined flow rate. A driver is drivingly connected to the metering units and configured to drive the metering units at a constant speed. 
     According to another aspect of the invention, the reactant fluid dispenser is configured to maintain a constant ratio between the flow rates of the reactant fluids. 
     According to another aspect of the invention, the metering units of the reactant fluid dispenser are configured to move their respective reactant fluids using positive piston displacement. The ratio between the flow rates of the reactant fluids is changeable by replacing a piston of at least one of the metering units with a piston of different size. 
     According to another aspect of the invention, the driver includes a hydraulic cylinder connected to the metering units and a pressure compensated flow control valve connected to the hydraulic cylinder and configured to control driver speed. 
     According to another aspect of the invention, the reactant fluid dispenser includes first and second reactant fluid sources configured to dispense the first and second reactant fluids. A first metering unit is connected between and is in fluid communication with the first reactant fluid source and the applicator gun. A second metering unit is connected between and is in fluid communication with the second reactant fluid source and the applicator gun. A driver is connected to the first and second metering units and is configured to move the reactant fluids at constant respective flow rates. The driver is adjustable to alter the ratio between the respective flow rates of the reactant fluids. 
     According to another aspect of the invention, the driver includes two hydraulic cylinders, each cylinder being drivingly connected to one of the metering units. The driver includes two proportional directional flow control valves, each valve connected to and configured to control the movement of one of the hydraulic cylinders. 
     According to another aspect of the invention, the reactant fluid dispenser includes fluid pre-heaters disposed upstream from the respective metering units and configured to heat the respective reactant f luids before they enter the metering units. 
     According to another aspect of the invention, the reactant fluid dispenser includes two fluid post-heaters, each post-heater disposed downstream from one of the metering units. The dispenser also includes two heat sensors, each one of which is disposed in one of the reactant fluids and configured to monitor reactant fluid temperature. A controller is connected to the post-heaters and the heat sensors and is configured to control reactant fluid temperatures by adjusting heat output of the respective post-heaters in accordance with fluid temperature information fed back to the controller from the respective heat sensors. 
     According to another aspect of the invention, the controller includes a programmable logic controller configured to monitor and send signals to adjust the temperature, pressure, volume and flow rate of the reactant fluids. 
     According to another aspect of the invention, the cross-sectional areas of the mixing chamber fluid inlet openings are different. This allows the gun applicator to mix reactant fluids in proper proportions despite differences in viscosity. A forward edge of each fluid inlet opening is aligned in the direction of a longitudinal axis of the mixing chamber to expose each fluid inlet opening at the same time for proper reaction of the components. 
     According to another aspect of the invention, a method is provided for applying the multi-component foamable fluid plastic material. According to the method a heater is provided adjacent the support body structure. The support body structure is then heated by energizing the heater and a flow of the reactant fluids is provided through the mixing chamber fluid inlets and into the mixing chamber. Once mixed, the reactant fluids are dispensed from the mixing chamber. 
     According to another aspect of the inventive method, the support body structure is heated to a temperature generally equal to that of an optimum temperature for reaction of the reactive fluids. 
     According to another aspect of the inventive method, at least one heating element is provided in the support body structure adjacent the mixing chamber fluid inlets. The heating element is energized to transfer heat energy into the support body structure. 
     According to another aspect of the inventive method, a gun temperature control system is provided that includes a temperature sensor configured to monitor support body structure temperature. Heater temperature is controlled based on temperature sensor inputs received from the temperature sensor. 
     According to another aspect of the inventive method, a gun temperature control system is provided that includes two temperature sensors configured to monitor body structure temperature at respective locations adjacent the respective mixing chamber fluid inlets. Two heating elements are provided on the support body structure, each heating element disposed adjacent one of the mixing chamber fluid inlets. The temperatures of the two heating elements can then be controlled separately based on temperature sensor inputs received from the respective temperature sensors. 
     According to another aspect of the invention, an additional method is provided for applying the multi-component foamable fluid plastic material in which a second one of two reactant fluids has a relatively low viscosity. According to this method an applicator gun is provided that includes a first fluid inlet opening disposed in a flat portion of a wall of the sleeve that is disposed parallel to the flat portion of the interior surface of the sleeve receptacle, and a seal that is disposed around the first fluid inlet opening between the flat portions of the sleeve and the sleeve receptacle. 
     According to another aspect of the inventive method, an applicator gun apparatus is provided that includes a second fluid inlet opening disposed in a second flat portion of the interior surface of the sleeve receptacle generally opposite the first fluid inlet opening, and in which a second flat portion of the sleeve wall is disposed parallel to and adjacent the second flat portion of the interior surface of the sleeve receptacle. A second seal is disposed around the second mixing chamber fluid inlet between the second flat portions of the sleeve receptacle and of the sleeve. A flow of the second reactant fluid of relatively low viscosity is then provided into the mixing chamber through the second fluid inlet opening. 
     According to another aspect of the invention, a method is provided for applying a multi-component foamable fluid plastic material that includes providing a reactant fluid dispenser configured to supply the reactant fluids to an applicator gun mixing chamber through mixing chamber fluid inlets at respective constant flow rates. The reactant fluid dispenser is connected to the applicator gun, the reactant fluids are provided in the reactant fluid dispenser, the ratio between fluid flow rates is adjusted to supply the reactant fluids to the applicator gun mixing chamber at predetermined constant respective optimum flow rates for proper mixing, the reactant fluid dispenser is actuated to supply the reactant fluids to the applicator gun mixing chamber, and the applicator gun is actuated to dispense the resulting plastic material foam from the mixing chamber. 
     According to another aspect of the inventive method, the step of providing a reactant fluid dispenser includes providing a driver drivingly connected to first and second metering units and configured to move the respective first and second reactant fluids at constant predetermined flow rates, the metering units being configured to move their respective reactant fluids using positive piston displacement. The fluid flow ratio is adjusted by changing the flow rate of one the reactant fluids by replacing a piston of one of the metering units with a piston of different size. 
     According to another aspect of the inventive method, a driver is provided that includes a hydraulic cylinder drivingly connected to the metering units and a pressure compensated flow control valve connected to the hydraulic cylinder and configured to control driver speed. The fluid flow ratio adjusted by adjusting the flow rates of the reactant fluids by adjusting the flow control valve. 
     According to another aspect of the inventive method, a reactant fluid dispenser is provided that includes a driver connected to first and second metering units and configured to move the reactant fluids at constant respective flow rates, the driver being adjustable to alter the ratio between the respective flow rates of the reactant fluids. The flow rates of the first and second reactant fluids are adjusted by adjusting the driver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational side view of the preferred embodiment of the present invention, showing the optional trigger handle; 
     FIG. 2 is a front end view of the preferred embodiment, without the optional trigger handle, partially in cross section; 
     FIG. 3 is a rear end view of the preferred embodiment, without the optional trigger handle; 
     FIG. 4 is a bottom view of the preferred embodiment of the present invention, partially broken away; 
     FIG. 5 is a cross sectional view taken along lines  5 — 5  of FIG. 2 showing a valve needle of the invention in a rearward open position; 
     FIG. 6 is a cross sectional view similar to FIG. 5 showing an alternate embodiment showing the valve needle in a forward closed position; 
     FIG. 7 includes front, side and back elevational views of one half of the mix head of the embodiment of FIG. 6; 
     FIG. 8 is a cross-sectional view taken along lines  8 — 8  of FIG. 7; 
     FIG. 9 is a schematic view of the entire apparatus for applying a foamable material; 
     FIG. 9 a  is a schematic view of the reactant fluid delivery system of the present invention; 
     FIG. 9 b  is a schematic view of an alternate reactant fluid delivery system according to the present invention; and 
     FIG. 10 is a side elevational view of the reactant fluid delivery system of FIG. 9 b.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An apparatus for dispensing and applying a multi-component foamable fluid plastic material is generally shown at  10  in the Figures. The embodiment shown in FIG. 1 shows an applicator gun generally indicated at  12 . The applicator gun  12  may include an optional trigger handle  14 . Opening and closing of the gun is controlled by an electronic controller in a manner described below. The electronic controller is shown in the form of a control panel at  128  in FIG.  9 . The optional trigger handle  14  is used as an alternate means to send an electronic signal to the electronic controller  128  which, in turn, sends a signal to selectively operate a hydraulic cylinder assembly, generally indicated at  16  and thereby open and close the gun  12 . It will be appreciated, however, that use of the optional trigger handle assembly  14  is not necessary to the operate of the gun. 
     The controller  128  controls all aspects and functions of every part of the dispenser system and gun  12 . The system can be used in one of two ways: “manual” mode or “automatic” mode. When manual mode is utilized, the dispenser system and gun will respond to manual inputs to dispense foam, i.e., via a signal from the optional trigger handle  14  or the pressing of a dispense button on a touch screen of the electronic controller  128 . When in manual mode, robot or automation signals generated by the controller  128  are disregarded. 
     When the automatic mode is selected, the metering system and gun will respond only to the signals sent via the electronic controller  128  to dispense foam, i.e., via a discrete signal from a robot controller or some other automation control or a signal sent over a network such as a remote I/O or “data highway plus” or RS 232 . When in automatic mode, manual inputs are disregarded. Therefore, the optional trigger handle  14  is a means for a user to send a dispense signal to the dispenser controller within the electronic controller  128  when the system is used in manual mode. 
     The trigger handle  14  can be likened to a dispense signal that a robot controller would send to a dispense control in the electronic controller  128  when the system is used in automatic mode. Thus, the dispenser control within the electronic controller  128  controls the applicator gun  12 . The trigger handle  14  or robotic controller can request that a preprogrammed/preselected shot be dispensed from the gun  12  by sending a signal to the controller  128 , but nothing happens unless and until the electronic controller  128  causes it to happen. 
     It is to be appreciated that the gun  12  is always opened and closed by a signal sent by the electronic controller  128 . The trigger handle  14  merely provides an alternate means to send a dispense signal to the electronic controller  128  which responds by controlling the opening and closing of the gun  12 . When the trigger handle  14  is not used, the opening and closing of the gun  12  is robotically controlled by the electronic controller  128 . 
     As best seen in FIG. 5, the hydraulic cylinder assembly  16  includes a hydraulic cylinder body  18  connected to a hydraulic cylinder head  20  in any suitable manner. An appropriate seal, such as an O-ring seal  21  is disposed between the hydraulic cylinder body  18  and hydraulic cylinder head  20 . A hydraulic piston  22  reciprocates within a bore  24  in the hydraulic cylinder body  18 . A pair of hydraulic lines is in fluid communication with the bore  24 . The hydraulic lines enter through openings  25   a ,  25   b  (FIG. 1) in the hydraulic cylinder assembly  16 . One of the hydraulic line openings  25   a  is positioned such that it allows hydraulic fluid to flow into and out of the bore  24  forward of the piston  22 . The second hydraulic line opening  25   b  is positioned such that it allows hydraulic fluid to flow into and out of the bore  24  rearward of the piston  22 . In this manner, hydraulic actuation of the piston  22  is controlled in a normal manner, well known in the art. A plurality of suitable seals  26 , such as O-ring energized lip seals are disposed about the piston  22  to prevent the flow of hydraulic fluid around the piston  22  within the bore  24 . A solenoid directional valve is used to control the hydraulic cylinder assembly  16  to open and close the gun  12 . 
     A connecting rod  28  is secured to the piston  22  in any suitable manner. In the preferred embodiment, the connecting rod  28  is fixed to a piston washer  30  that is retained in the piston  22 . The piston washer  30  moves with the piston  22 , thereby moving the connecting rod  28 . Suitable seals  32 , such as O-ring seals are disposed between both the piston washer  30  and piston  20  and between the piston washer  30  and connecting rod  28 . The hydraulic cylinder head  20  includes a bore  34  for receiving the connecting rod  28 . Further, a hydraulic seal  36  is disposed about the connecting rod  28  and retained within the hydraulic cylinder head  20 . The hydraulic seal  36  prevents the flow of hydraulic fluid about the connecting rod  28  and into the bore  34  in the hydraulic cylinder head  20 . A rod wiper  37  is also disposed about the connecting rod  28  in the hydraulic cylinder head  20  to wipe debris from the connecting rod  28 . 
     The hydraulic cylinder assembly  16  is connected to a support body structure in the form of a gun body, generally indicated at  38  in FIGS. 1-6. The gun body  38  includes a longitudinally extending bore, shown at  40  in FIG. 5, for receiving the connecting rod  28  (and valve needle as described below). 
     The gun body  38  includes a fluid inlet manifold shown at  42  in FIGS. 1-4. The fluid inlet manifold  42  is mounted on the gun body  38  to allow the respective components of the foamable plastic material to flow into the gun body  38  (as best seen in FIGS.  2  &amp;  3 ). The fluid inlet manifold  42  includes at least a pair of openings  44 . Each opening  44  is adapted to receive a valve assembly generally indicated at  46  in FIGS. 1-3. The valve assembly  46  includes a valve stem  48  that is maintained within the opening  44  by a retainer  50 . The retainer  50  is secured within the opening  44  in any suitable manner. The valve stem  48  is preferably threadedly retained within the retainer  50 . Suitable seals  52 , preferably O-ring seals, are disposed between the retainer  50  and the gun body  38 , and between the valve stem  48  and retainer  50  to prevent the flow of fluid therepast. 
     As is best shown in FIG. 2, the valve assembly  46  further includes a valve  54  and a valve washer  56 . A screw  58  is disposed within the valve  54  and valve washer  56 . The screw  58  is threadedly received within a bore in the valve stem  48 . The screw  58  connects the valve  54  and valve washer  56  with the valve stem  48 . The valve  54  has a tapered end  60  that seats against the fluid inlet manifold  42  when the valve assembly  46  is in the closed position to prevent reactant fluid flow into the gun. When the valve assembly  46  is in the normally open position, the tapered end  60  is unseated from the gun body and allows reactant fluid to flow therepast. The valve assembly  46  is moved between the closed and normally open positions by turning the valve stem  48 . Rotation of the valve stem  48  causes respective movement of the valve  46 . By allowing for manual shut off of the reactant fluid flow at the valve assembly  46 , the flow of reactant fluid into the gun body can be manually controlled to allow servicing of the gun  12  or the like. 
     The gun body  38  includes a fluid inlet or fluid inlet passage, generally indicated at  62  in FIGS. 1-3 and  5  and at  62 ′ in FIG. 6 (a prime designation is used to denote similar components having modified structures among the embodiments), connected to each of the openings  44 . While the inlet passage  62 ,  62 ′ may take any suitable configuration, in the preferred embodiment, each fluid inlet passage  62 ,  62 ′ comprises three passage components  64 ′;  65 ,  65 ′ and  66 ,  66 ′. An inlet passage component  64 ′ is disposed in the fluid inlet manifold  42 . The reactant fluid hose attaches to the fluid inlet manifold  42  at the rear thereof, where the inlet passage component  64 , commences (FIG.  3 ). The inlet passage component  64 ′ terminates in the opening  44 . A transverse passage component  65 ,  65 ′ is disposed within the fluid inlet manifold  42  and is oriented transverse to the longitudinal direction of the gun body  38  and traverse to the inlet passage component  64 ′. This transverse passage component  65 ,  65 ′ is in fluid communication with the opening  44 . The tapered end  60  of the valve  54  is oriented at the top of the transverse passage component  65 ,  65 ′ and seals the top end when valve assembly  46  is in the closed position. The bottom end of the transverse passage component  65 ,  65 ′ is connected to a longitudinal passage component  66 ,  66 ′. The longitudinal passage component  66 ,  66 ′ extends generally in the longitudinal direction of the gun body  38 . 
     As shown in FIGS. 5 and 6, the longitudinal passage component  66 ,  66 ′ includes a ball check assembly generally indicated at  68  therein. The ball check assembly  68  can be of any type well known in the industry. As shown, the ball check assembly  68  primarily includes a ball  70  connected to a pin  72 . The pin  72  is operatively connected to a spring  74 . A ball seat  76  is also operatively associated with the spring  74 . In operation, the ball  70  is normally biased by the spring  74  against the ball seat  76  such that fluid cannot flow past. As fluid is introduced through the fluid passage  62 ,  62 ′ fluid flows through the longitudinal passage component  66 ,  66 ′ and forces the ball  70  out of engagement with the ball seat  76  to allow reactant fluid flow toward the mixing chamber, as will be described below. The ball check assembly  68  prevents the flow of fluid in the opposite direction, by the action of the ball  70  with the ball seat  76 . A suitable seal  78 , such as an O-ring seal may be disposed between the ball seat  76  and mix head  82  adjacent the ball seat  70 . 
     The longitudinal passage component  66 ,  66 ′ of the fluid inlet passage is connected to a mixing chamber fluid inlet  80 ,  80 ′. That is, the longitudinal passage component  66 ,  66 ′ and the mixing chamber fluid inlet  80 ,  80 ′ are in fluid communication. The mixing chamber fluid inlet  80  is downstream of the ball check assembly  68 . 
     The mixing chamber fluid inlet  80 ,  80 ′ preferably extends generally transverse to the longitudinal component  66 ,  66 ′ of the fluid inlet. A cap  81  closes the mixing chamber fluid inlet  80 ,  80 ′ in one direction to prevent fluid flow outward of the gun  12 . In the embodiments shown, the mixing chamber fluid inlet  80 ,  80 ′ tapers from a generally wider top portion connected to the longitudinal passage component  66 , to a generally narrower bottom portion that is connected to the mixing chamber at an orifice or fluid inlet opening. 
     A mix head  82  is connected to the forward portion of the gun body  38 . The mix head  82  is secured to the gun body  38  with suitable fasteners, such as cap screws  84  (FIG.  2 ). The mixing chamber fluid inlet  80 ,  80 ′ is contained within the mix head  82 . 
     The mix head  82  contains a sleeve receptacle in the form of a longitudinal bore  86  extending through the mix head  82 . The longitudinal bore  86  houses a sleeve  88 ,  88 ′. The sleeve  88  is maintained in the bore  86  by including an outer annular flange  89 . The outer annular flange  89  engages the mix head  82  to prevent axial movement of the sleeve  88 ,  88 ′ outwardly of the gun  12 . 
     The sleeve  88 ,  88 ′ also has a longitudinal bore therethrough, which defines the mixing chamber  90 . The mixing chamber fluid inlet  80 ,  80 ′ also passes through the wall of the sleeve  88 ,  88 ′ in a direction generally transverse to the longitudinal axis of the sleeve  88 ,  88 ′. The mixing chamber fluid inlet  80 ,  80 ′ is thus in fluid communication with the mixing chamber  90  to allow reactant fluid to enter the mixing chamber  90 . 
     The mixing chamber  90  includes an outer end  91  through which the reacted fluid exits the gun  12 . Thus, reactant fluid enters the mixing chamber  90  through the inlets  80 ,  80 ′ and the mixed reacted fluid exits the mixing chamber  90  through the outer end  91 . 
     As shown in FIG. 5, the fluid passage  62  and mixing chamber fluid inlets  80  have generally the same diameter for each of the fluid inlet openings. This works well when standard reactants are used as described above, having comparable ratios of the volumes of the inlet fluids needed for the reaction, and comparable viscosities of the reactant fluids. 
     As shown in FIG. 6, the fluid passages  62 ′ may have different diameters. Furthermore, the diameters of the respective mixing chamber fluid inlets  80 ′ and fluid inlet openings may be different. This becomes important when the ratio of the volume of the reactant materials varies and/or the viscosity of one of the reactant materials is substantially different than the viscosity of the other reactant material, such as, for example, when using the no or low isocyanate reactant as described above. The mixing chamber fluid inlets  80 ′ are machined to sizes that will provide respective desired fluid pressures for a given viscosity and flow rate. In addition, as shown in FIG. 6, the portion of the mixing chamber fluid inlet  80 ′ passing through the sleeve  88 ′ to the fluid inlet opening, may be slightly angled. This allows the reactant fluid to be more evenly dispersed over the reactant fluid stream entering from the opposite side of the mixing chamber  90 . In this manner, better mixing of the reactant fluid stems is achieved to achieve a more complete reaction. 
     In addition, as shown in both FIGS. 5 &amp; 6, two inlet passages  62 ,  62 ′ are shown. It will be appreciated that any number of inlet passages  62 ,  62 ′ may be used within the scope of the present invention depending on the number of reactant streams necessary for a proper reaction. It is preferred, however, that the forward edges of the mixing chamber fluid inlets  80 ,  80 ′ be aligned in the direction of the longitudinal axis of the sleeve  88 . This is important because when mixing commences, as will be described below, each mixing chamber fluid inlet  80 ,  80 ′ preferably is exposed at the same time for proper reaction of the components. 
     The gun  12  further includes a valve needle  92 . The valve needle  92  is disposed for reciprocating movement within the mixing chamber  90 . The valve needle  92  is removably connected to the connecting rod  28  at the end of the connecting rod opposite that connected to the piston  22 . 
     In the embodiments shown, the removable connection between the connecting rod  28  and valve needle  92  is as follows. The end of the connecting rod  28  includes an annular flange  29 . Similarly, the valve needle  92  includes an annular flange  94  at one end. A coupler generally indicated at  96  has two halves  98 ,  100 . The coupler assembly  96  surrounds each of the annular flanges  29 ,  94 . When the two halves  98 ,  100  are placed around the flanges  29 ,  94  a retainer sleeve  101  is placed about the coupler  96  to secure the halves  98 ,  100  together. The retainer sleeve  101  comprises cylindrical tubing. A pair of O-rings  102  then snap into grooves (in the outer surface of the halves  98 ,  100 ) to hold the sleeve  101  and prevent sliding movement of the sleeve  101  relative to the halves  98 ,  100 . As shown in FIG. 5, each of the halves  98 ,  100  includes a leg  103  at each end to engage the respective flanges  29 ,  94 . With the coupler  96  secured in this manner, the valve needle  92  is secured to the connecting rod  28 . 
     To disconnect the valve needle  92  from the connecting rod  28 , the user must simply remove each of the O-rings  102  from each of the halves  98 ,  100 . The sleeve  101  is then removed from the halves  98 ,  100 . The halves  98 ,  100  can then be separated and the valve needle  92  can be removed from the connecting rod  28 . A quick connect/disconnect coupler  96  of the type shown in the Figures allows the valve needle  92  to easily be removed from the mixing chamber  90  to allow cleaning of the mixing chamber  90 , or similar service on the gun. While one type of coupler  96  has been shown, it will be appreciated that any type of coupler that allows for relatively quick connection/disconnection between the valve needle  92  and connecting rod  28  falls within the scope of the present invention. 
     The coupler  96  can be engaged/disengaged with no more tools than one small screwdriver. The coupler  96  allows for axial and radial misalignment between the valve needle  92  and the hydraulic cylinder connecting rod  28 . The coupler  96  can be engaged/disengaged with the gun stuck in either the open or closed position. 
     The sleeve  88  extends outwardly of the mix head  82  in the forward direction. The sleeve  88  has an outer surface that includes male threaded position forward of the mix head  82 . A lock collar  104  is disposed about the end of the sleeve  88  that protrudes from the mix head  82 . The lock collar  104  has a female threaded position that engages the male threaded portion of the sleeve  88 . Thus, the lock collar  104  is threaded onto the male threaded position to thereby secure the lock collar  104  with the sleeve  88  and prevent axial movement of the sleeve  88  through the mix head  82  in the direction toward the gun body  38 . Thus, the sleeve  88  is prevented from axial movement outward of the gun  12  by the annular flange  89  engaging the mix head  82 , and is prevented from axial movement inward of the gun  12  by the threaded connection between the sleeve  88  and the lock collar  104 . 
     In the embodiment of FIG. 5, the sleeve  88  and the mix head  82  are accurately machined to provide a very close fit between the respective parts. Both the exterior wall of the sleeve  88  and interior wall of the mix head  82  are generally cylindrical. It is important that the sleeve  88  and mix head  82  are in very close proximity. That is, the dimensional tolerance between the sleeve  88  and mix head  82  is very small, as is known in the art. If the space between the sleeve  88  and mix head  82  is too great, the reactant fluids may seep about the periphery of the sleeve  88  and react in the longitudinal bore  86  and outside of the mixing chamber  90 . Of course, this is undesirable. The components using the standard reactants defined above allow for the sleeve  88  and mix head  82  to be machined to a close fit without the need to further seal the mixing chamber fluid inlet  80  at the connection of the sleeve  88  and mix head  82 . Notwithstanding the close fit that prevents fluid flow about the exterior of the sleeve  88 , suitable seals  108 , such as O-ring seals may be placed between the sleeve  88  and mix head  82  forward and rearward of the mixing chamber fluid inlet  80 . 
     Similarly, the valve needle  92  and interior surface of the sleeve  88  are accurately machined to provide a very close fit between the respective parts. Both the valve needle  92  and interior surface of the sleeve  88  are cylindrical. It is important that the valve needle  92  and the interior surface of the sleeve are in very close proximity. This is because the valve needle  92  serves two important functions. First, when the needle  92  is in a forward closed position (shown in FIG. 6) it covers the mixing chamber fluid inlets  80 , 80 ′ so as to act as a valve and prevent the flow of the reactant fluids into the mixing chamber  90 . As the valve needle  92  moves to the rearward or open position (As shown in FIG.  5 ), the valve needle  92  moves past the mixing chamber fluid inlets  80 ,  80 ′, exposing them to the mixing chamber  90  at the same time. 
     After the desired amount of reacted material has exited the mixing chamber  90 , the valve needle  92  moves from the open to the closed position. The second important function of the valve needle  92  takes place during this movement. Specifically, the valve needle  92  acts to clean the mixing chamber  90  of residual reactant and reacted fluids by scraping the wall of the mixing chamber  90 . This movement causes the remaining fluid in the mixing chamber  90  to be purged from the mixing chamber  90 . When the valve needle  92  is in the closed position, the end of the valve needle  92  is preferably even with the opening at the outer end  91  of the mixing chamber  90 , or the valve needle  92  extends slightly forwardly of the outer end  91  and out of the mixing chamber  90 . This aids in purging any reacted or remaining reactant fluids from the mixing chamber  90 . 
     As shown in FIG. 6, the valve needle  92  may also include a groove  110  to aid in scraping the wall of the mixing chamber  90 . The groove  110  scrapes the build up (sometimes referred to as varnishes) from the bore of the sleeve that defines the mixing chamber  90 . The groove  110  scrapes the bore as the valve needle  92  moves in both directions (that is while opening and closing the gun). Another function of the groove  110  is to minimize the contact area between the valve needle  92  and the sleeve wall. In this manner, the groove  110  also helps break the metal-to-metal bond that tends to form between the valve needle  92  and sleeve wall that can seize the gun. 
     In the preferred embodiment, the groove  110  is helical. A second helical groove (as shown in FIG. 6) may also be incorporated which is circumfrentially offset from the first helical groove. The helical grooves  110  should be oriented such that the groove  110  can not simultaneously expose the mixing chamber fluid inlets  80 ,  80 ′. That is, the two helical grooves cannot connect the mixing chamber fluid inlets  80 ,  80 ′ to the same groove  110 . As shown in FIG. 6, each different helix is connected to the different inlets  80 ,  80 ′. If only a single helix is used, its pitch must be such that it does not connect the inlets  80 ,  80 ′. 
     The valve needle  92  may also include a pair of annular grooves  112 . The annular grooves are disposed such that one of the annular grooves  112  is positioned forward of the mixing chamber fluid inlets  80 ,  80 ′ when the valve needle  92  is in the forward closed position. The second of the annular grooves  112  is positioned rearward of the mixing chamber fluid inlets  80  when the valve needle  92  is in the forward closed position. The annular grooves  112  serve to prevent reactant fluids from passing thereby. That is, any residual reactant fluid will collect in the annular groove  12  and react, thus creating a seal at that point between the valve needle  92  and the interior wall of the mixing chamber  90 . 
     In the alternate embodiment of the sleeve  88 ′, as shown in FIGS. 6 &amp; 7, and mix head  82 ′, as shown in FIG. 6, the exterior wall of the sleeve  88 ′ is generally rectangular at the area where it engages the sleeve receptacle of the mix head  82 ′. Similarly, the interior surface  86 ′ defining the sleeve receptacle of the mix head  82 ′ is rectangular to mate, in close proximity with, the exterior wall of the sleeve  88 ′. The mix head  82 ′ includes at least one recess  114  in a flat sidewall of the sleeve receptacle  86 ′. The recess  114  surrounds the mixing chamber fluid inlet  80 ′. Alternatively, the recess  114  could be placed in the exterior wall of the sleeve  88 ′. 
     It is preferred that, a recess  114  surrounds each mixing chamber fluid inlet  80 . A suitable seal  116 , such as an O-ring seal is disposed in the recess  114  and is compressed between the sleeve  88 ′ and the sleeve receptacle  86 ′ of the mix head  82 ′. The O-ring  116  prevents the reactant fluid from passing between the sleeve  88 ′ and the sleeve receptacle  86 ′ of the mix head  82 ′. This sealing arrangement is particularly effective when one or more of the reactant fluids are not relatively viscous, and could seep through the press fit arrangement of the previous embodiment of FIG. 4 as discussed above. Furthermore, when the sleeve  88 ′ having a generally rectangular configuration is used, it is preferred to make the mix head  82 ′ in two halves, one of which is shown in FIG.  7 . The halves are split in the longitudinal direction along the top and bottom surfaces. It is preferred that the split not be located on the sides including the recesses  114 . Furthermore, while the sleeve  88 ′ is preferably rectangular, it may take other configurations. It has been found, however, that a relatively flat interface between the sleeve receptacle  86  of mix head  82 ′ and the sleeve  88 ′, and the incorporation of a recess  114  to receive an O-ring  116 , provides a suitable sealing arrangement. 
     The gun body  38  further includes at least one heating element  118 . The heating element  118  is positioned in the gun body  38  in proximity to the fluid passage  62 ,  62 ′ to maintain the reactant fluids at an elevated temperature necessary for proper reaction. The heating element  118  heats the gun body  38  sufficiently to allow the first shot of reacted material to be useful. In the preferred embodiment, two heating elements  118  are used. One heater  118  is placed next to each of the inlet passages  62 ,  62 ′. The use of two heaters  118  results in properly balanced heating of the gun  12 . 
     The heating element  118  heats the gun body  38  to a temperature to maintain the reactant fluids at a suitable reaction temperature. As described below, the reactant fluids are typically preheated to a suitable reaction temperature before being transmitted to the application gun  12 . Typically, at start-up, the gun body  38  is not at a suitable temperature for the foaming reaction to occur. In prior art assemblies, the heat energy contained in the reactant fluid streams, and the heat energy given off by the foaming reaction is used to heat the gun body and maintain it at a suitable reaction temperature. This is undesirable because the first shots of the reactant fluid existing the mixing chamber  90  are not useable. The heating element  118  is used to preheat the gun body  38  so that heat energy is not dissipated from the reactant fluid streams, thus maintaining the reactant fluid at a suitable reaction temperature so that the first shot emanating from the mixing chamber  90  is useable. The temperature of the gun body is monitored by a temperature sensor  119  (FIG.  1 ). The temperature sensor comprises a thermocouple feedback system that uses a heating control washer thermocouple  119 . The sensors  119  could also be RTD&#39;S. The sensors  119  provide a temperature feedback signal to the electronic controller  128  so that it can accurately control the gun temperature by controlling the power sent to the heating elements  118  in the gun  12 . 
     In the preferred embodiment, a pair of heating elements  118  is used. Each heating element  118  is preferably an electric cartridge heater. There are many other ways of heating the gun body  38 . For example, the heating element  118  may comprise coring inside the gun body  38  through which a heated liquid such as a water/glycol mixture is run. 
     The gun body  38  also includes a pair of proximity switches  120 ,  122  (FIG. 4) located on the bottom side thereof. The proximity switches  120 ,  122  may be mounted on a bracket  124 . The proximity switches  120 ,  122  detect the two positions of the gun  12 . The two switches  120 ,  122  are a gun closed switch  120  and a gun open switch  122 . The gun closed switch  120  detects when the gun  12  is closed and the gun closed switch  120  is on. The open switch  122  detects when the gun  12  is open and the open switch  122  is on. 
     The electronic controller  128  controls the entire dispensing system. The proper sequencing of the gun  12  is as follows. 
     When the electronic controller  128  receives a dispense signal (either in manual mode by the trigger handle  14  or push button, or in automatic mode via robot or automation control signal) and providing a shot type has been selected in the electronic controller  128  and providing the system  10  is ready to dispense (not refilling, at pressure at temperature, not faulted, etc.) the controller  128  begins the sequence. First, the controller  128  energizes a directional valve to send hydraulic fluid to the gun  12  to open it. As the gun  12  opens, the gun closed proximity switch  120  signal goes from “on” to “off.” When the signal goes off, the controller  128  causes the metering unit  130  to advance a predetermined amount (volume) at a predetermined rate (flow rate). When the gun open  122  proximity switch goes on, the controller  128  stops energizing the open gun directional valve which in turns stops hydraulic fluid flow to the gun  12  to stop the opening motion of the gun  12 . When the controller  128  has sensed (via a position feedback transducer) that the metering unit  130  has displaced the proper volume of reactants for the shot requested, the controller  128  energizes the closed gun solenoid directional valve (A three position, double solenoid valve) and causes the metering unit  130  to stop. When the gun-closed proximity switch  120  goes on, the controller  128  stops energizing the closed gun directional valve which in turn stops hydraulic fluid flow to the gun  12  trying to close it. The controller  128  then reports the success (or lack of) of the shot dispensed and whether or not it is ready for the next shot. 
     The gun  12  of the apparatus  10  has been described in detail above. The apparatus  10  also includes a reactant fluid delivery system or dispenser generally indicated at  126  in FIG.  9 . The reactant fluid dispenser  126  includes the electronic controller  128 , and hydraulic power unit  140  as will be hereinafter described. The reactant fluid dispenser  126  also includes a metering unit  130  and a reactant fluid heater generally indicated at  134 . 
     Preferably, the metering unit  130  is a fixed ratio positive displacement metering unit with constant flow rate control. (FIG. 9) The positive displacement metering unit  130  can be a single-acting piston displacement (lance type) metering assembly with positive shut-off (power) flow valves  150  on both the inlet  152  and outlet  154  of the meter assembly  130  with a driver  156 . (FIG. 9 a ) The driver  156  could include a heavy-duty hydraulic cylinder  158  or an electric servomotor with a ball screw actuator. 
     Alternatively, the metering unit  130  could include a precision tool steel gear pump with driver. The driver could be a hydraulic motor or an electric drive servomotor with gear reducer. 
     The constant flow rate of the metering unit  130  can be achieved in a number of ways. For example, a constant flow rate of the metering unit  130  can be achieved by using a hydraulic cylinder/motor. A pressure compensated flow control or proportional flow control valve  160  with hydrostat  162  is used to control the speed of the driver  156 . (FIG. 9 a ) By doing so, the load on the driver  156  (from the meter assembly  130 ) can vary because of pressure or viscosity changes of the fluid, but the driver  156  will hold speed because of the pressure compensated flow of the hydraulic fluid to the driver  156 . Thus, the flow of reactant fluid from the metering unit  130  is constant. Alternatively, the constant flow rate of the metering unit  130  can be achieved by using an electric drive servomotor with ball screw actuator or servomotor with a gear reducer. An amplifier that powers the servomotor is configured for velocity mode. By doing this, the servo drive will hold speed against a variable load because of the feedback circuit between the servomotor and its amplifier. 
     Another method for achieving constant flow rate is to use any of the driver configurations listed above, but a position and velocity loop is closed between a servo control in the controller  128  and a position feedback transducer  164  in the metering unit. The position feedback transducer  164  may include a linear encoder when used for lance meters or may include a rotary encoder when used for gear pumps. 
     A schematic diagram for a reactant fluid dispenser  126  including a two component fixed ratio positive displacement constant flow metering unit  130  is shown in FIG. 9 a  as used on conventional foam production dispenser systems. The ratio of reactant fluid flow rates is fixed but is changeable by changing one or both of the meter assembly  130  pistons/rod diameters and packings. A position transducer  164  (in this example) is used for position control only. 
     FIG. 9 b  shows a two component, adjustable ratio, positive displacement constant flow rate dispenser  126   b  as used for the alternate reactants with no or low isocyanates. (Elements of dispenser  126   b  shown in FIGS. 9 b  and  10  that are the same or analogous to elements shown in FIGS.  9  and/or  9   a  bear the same reference numeral only with the suffix “b”.) The adjustable ratio dispenser system  126   b  allows adjustability of the reactant fluid flow rate ratio by changing the rates of one of the metering units  130   b  versus the rate of the other  130   b . A position transducer  164   b  in the form of a linear encoder is used with a servo control for more precise position and velocity control. The meter assemblies  130   b  are heated and controlled since fluid heaters (preheaters)  134   b  are included upstream of the inlets  152   b  of the meter assemblies  130   b  (as described below). This dispenser  126   b  thus meters heated fluid, which is more accurate than heating the fluid after it is metered. 
     The metering unit  130 , in the preferred embodiment, is a single acting unit. That is, the metering unit delivers reactant fluid in only one direction of the stroke of the unit. The metering unit  130  also preferably uses a heavy-duty hydraulic cylinder drive  156 . The metering unit  130  is in fluid communication with and draws reactant fluid from supply tanks  132 . The reactant fluid supply tanks  132  contain the reactant fluids used in the system. 
     Filling of the metering units  130  never occurs while the gun  12  is open. At startup, when commanded to, or whenever the controller  128  determines that there is insufficient reactant material resident in the meters  130  to deliver a shot (via a position transducer) and the system is not dispensing, the controller  128  causes the metering units  130  to refill. This sequence is as follows. The outlet valves on a metering unit  130  are held closed. Inlet valves are opened. A proportional directional valve is controlled to cause the hydraulic cylinder to retract. The retracting cylinder draws the meter rods upwardly and out of the meter assemblies. While refilling, the controller  128  monitors pressure in both meters to insure that the supply of reactant fluid can keep up. If pressure in either meter falls below a minimum set point, the refill halts and waits for the supply pressure to rebuild before resuming the refill cycle. This is to prevent cavitating meters. If the refill is halted for too long, the controller  128  declares a refill fault and sends the appropriate signal. Once the hydraulic cylinder is fully retracted, the refill cycle ends and the proportional directional flow control valve is centered and the inlet valve closed. 
     Once the refill cycle ends, the recharge cycle begins. This cycle is as follows. The inlet and outlet valves on the meters are held closed. The proportional directional flow control valve is controlled to cause the hydraulic cylinder to advance at a slow rate. While the cylinder is advancing, the controller  128  monitors hydraulic pressure at the driving end of the hydraulic cylinder. The controller  128  also monitors meter pressures to insure that both sides are primed with reactant fluid and that one or the other meter does not over-pressurize. When the hydraulic pressure (at the cylinder) is equal to or greater than a minimum set point (a recharge pressure) the recharge cycle ends. When the recharge cycle ends, the proportional directional flow control valve is centered and on the preferred embodiment, outlet valves are opened. If all other aspects of the system are satisfactory, the controller  128  issues the appropriate ready to dispense signal. 
     In the preferred embodiment as shown in FIG. 9 a , to achieve the fixed ratio displacement of the reactant fluid, one hydraulic cylinder  158  drives both metering unit pistons at the same time. A single hydraulic drive unit  156  is connected to each of the pistons in the metering unit  130  to dispense the reactant fluid. 
     Alternatively, as shown in the FIG. 9 b  embodiment, each of the metering units  130   b  is shown connected to its own hydraulic cylinder  158   b . Each cylinder  158   b  uses a separate high performance proportional directional flow control valve  160   b . That is, two separate drives  156   b  are shown for driving the respective metering unit pistons that deliver the respective reactant fluids. This system is utilized for the alternate reactants with no or low isocyanates. 
     Fluid heaters  134  are preferably located at the outlet end of the metering units  130 . As shown in the FIG. 9 a  embodiment, each of the metering units  130  is connected to two fluid heaters  134  in series. The first fluid heater  134  of each pair is a preheater and generally set at a lower temperature setting than the post (second) heater  134 . The preheater  134  feeds partially heated reactant fluid to the post heater  134 . The post heater  134  is more accurately controlled by the controller  128  using thermocouple feedback including a thermocouple that is disposed in the reactant fluid itself to monitor the temperature of the fluid and not the temperature of the heater block. A reactant fluid hose  136  is connected to the outlet of each fluid post-heater  134 . The other end of each reactant fluid hose  136  is connected to one of the inlet passages  64  on the applicator gun  12 . Although, in the preferred embodiment, two metering units  130  are provided as are two pairs of fluid heaters  134 , other embodiments may include only a single metering unit connected to a single pair of fluid heaters or a single fluid heater. It will be appreciated that any number of metering units  130 , fluid heaters  134  and hoses  136  may be utilized within the scope of the present invention. 
     An alternative heating arrangement is shown in FIGS. 9 b  and  10 . According to the embodiment of FIGS. 9 b  and  10 , fluid heaters  134   b  are located upstream of the respective metering units  130   b . (In other embodiments the metering units  130  themselves may be heated.) It will be appreciated that fluid heaters  134  can be either upstream of the respective metering units  130 , on the metering units themselves, or on the outlet sides of the metering units  130 . 
     Each of the hoses shown at  136  in FIG. 9 includes a heating assembly  168 . Each hose preferably is wound with a heating element  170  to maintain the reactant fluid at its elevated temperature. The heating assembly  168  also includes a thermocouple feedback to the electronic controller  128 . Each of the heated hoses  136  is then wound together inside a bundler  138 . Preferably, the heating elements  170  on each of the hoses  136  are electric. All of the electric elements  170  around the hoses  136 , the hydraulic lines necessary for operation of the gun, and the electrical wiring between the gun and the electronic controller are similarly wrapped in the bundler  138 . 
     It will be appreciated, however, while the hoses  136  are preferably heated by electronic heating elements, other methods of heating the hoses  136  are within the scope of the present invention. For example, fluid lines can be placed around the hoses and a heated water/glycol system can be circulated through the system to maintain the hoses  136  at their elevated temperature. The bundler  138  is insulated to inhibit the loss of heat from the hoses  136 . 
     As stated above, the electrical control panel generally controls the temperature, pressure and volume (by controlling displacement of the fluid meter or the turning of a precision gear pump) and flow rate. The volume of the reactant fluid can be controlled independently of the flow rate which is controlled by the rate of advance of the piston within the metering unit or, alternatively, by the speed of a precision gear pump, depending upon which dispensing system is utilized. The control panel  128  is preferably a programmable logic controller that is used to monitor and send signals to adjust the temperature, pressure, volume and flow rate of the reactant fluids (as described above). The electrical control panel  128  is used to monitor the temperature of the gun heating element  118 . The electric control panel  128  monitors separate signals from PID temperature controllers to adjust the temperature. The electrical control panel  128  also controls the opening and closing of the gun  12 . 
     The hydraulic power unit  140  is in fluid communication with both of the metering units  130  and the gun  12  through the use of suitable hydraulic hoses and valving in any well-known manner. In the preferred embodiment, the hydraulic power unit comprises a double pump set up. First, a variable displacement piston pump is used for driving the metering unit  130  as set forth in detail above. A proportional directional valve controls the movement of the metering unit. A second pump, such as a vane pump or another variable displacement pump is also utilized to power and open and close the gun  12  via a directional solenoid valve as set forth in detail above. It is preferred that the hydraulic lines from the hydraulic power unit  140  to the gun  12  are also included within the heated bundler  138  as stated above. 
     In operation of the apparatus  10 , the electrical control panel  128  is energized, as is the hydraulic power unit  140 . The fluid heaters  134 , heated bundler  138  and heating elements  118  of the gun  12  are also energized to preheat these devices. The temperature of each of these is controlled by the electrical control panel  128 . Each of the fluid heaters  134 , heated bundler  138  and heating elements are allowed to reach a suitable reaction temperature. 
     Once the devices are at a suitable reaction temperature, and the metering units contain enough reactant fluid to deliver a shot, the electronic controller  128  sends a signal to open the gun  12 . As set forth above, as the valve needle is retracting, reactant fluids are delivered from the metering unit  130  to the gun  12 . It will be appreciated that no reactant fluid flow begins until the gun is switched to the open position and the unit is driving toward the open position as set forth above. When the valve needle  92  reaches the fully retracted position, the gun open switch senses the position of the valve needle  92  and signals the controller  128  to send a signal to the hydraulic actuator to stop movement of the valve needle  92 . An appropriate amount of reactant fluid is metered by the metering units  130 . The reactant fluid exits the respective fluid heater into the reactant fluid hoses  136  and passes through the hoses  136  in the bundler  138 . The hose  136  is maintained at a sufficient temperature to maintain the reactant fluid at the appropriate reaction temperature. The reactant fluid passes through the respective reactant fluid hose  136  to the respective inlet passage component  64 ′. The fluid then passes through the valve  54  into the fluid transverse passage  65 ,  65 ′. The reactant fluid passes through the transverse component  65 ,  65 ′ and into the longitudinal component  66 ,  66 ′ of the fluid passage  62 . The fluid then passes through the ball check assembly  68  and through the mixing chamber fluid inlet  80 ,  80 ′. Each of the reactant fluids is delivered to the mixing chamber  90  fluid inlets  80 ,  80 ′ as described above. 
     As the gun  12  moves to the open position and the valve needle  92  is drawn rearwardly under the actuation of the hydraulic cylinder assembly  16 , the mixing chamber fluid inlets  80  are exposed to the mixing chamber  90 . This allows the reactant fluid to enter the mixing chamber  90 . 
     The gun body  38  has been preheated as set forth above and remains heated by the heating elements  118  to maintain the gun body  38  and thereby the reactant fluids at the appropriate reaction temperature. Thus, reactant fluid at the appropriate reaction temperature enters the mixing chamber  90  and is allowed to react therein. The reacted fluid exits the mixing chamber  90  at its outward end  91 . Because the gun body  38  includes the heating element  118 , the first shot of the gun  12  is useable. When a sufficient amount of reacted material has been dispensed from the gun  12  (a shot), the controller  128  sends a signal to extend the valve needle  92  into the mixing chamber  90  under the actuation of the hydraulic cylinder assembly  16 , as set forth in detail above. 
     The valve needle  92 , as it passes through the mixing chamber  90 , pushes any remaining reacted fluid or reactant fluids out of the mixing chamber  90 . The helical groove  110  aids in scraping the sidewalls of the mixing chamber  90  to purge the mixing chamber of any remaining fluids. Once the valve needle  92  reaches its forwardmost position, the gun closed proximity switch  120  senses the position of the valve needle  92  and sends a signal to the electronic controller  128  which, in turn, sends a signal to the hydraulic unit to stop forward movement of the needle  92 . 
     The process can be repeated to deliver as many shots as are required for a particular application. Generally, the metering units are designed with enough capacity to dispense all the shots required for one job. The units will refill and recharge between jobs. If another shot is requested when the meter capacity is insufficient to displace it, the controller  128  causes the metering unit  130  to refill and recharge first before it responds to the request to dispense, as set forth above. This is one advantage of the gear pump type metering unit, that it never needs to refill. 
     The invention has been described in an illustrative manner, and is to be understood that the terminology that has been used is in the nature of description rather than of limitation. Obviously, many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced, otherwise as is specifically described.