Abstract:
A control valve for a fluid dispensing device comprises a valve stem, a valve body, a cap and an adjustment mechanism. The elongate valve stem has a flange. The valve body comprises a valve bore in which the elongate valve stem is configured to translate, and a flow path intersecting the valve bore and into which the valve stem penetrates. The cap is joined to the valve body to receive the valve stem such that the flange is positioned between the valve body and the cap. The adjustment mechanism changes a position of the cap with respect to the valve body to vary a distance between the cap and the flange which adjusts the force, and thereby the pressure at which the valve opens.

Description:
BACKGROUND 
     The present invention is related to liquid dispensing systems. In particular, the present invention relates to airless sprayers for dispensing paints, varnishes and the like. 
     Paint sprayers are well known and popular for use in painting of surfaces, such as on architectural structures, furniture and the like. Airless paint sprayers provide a high quality finish due to their ability to finely atomize liquid paint. These airless paint sprayers are typically coupled to a paint source, include a pumping mechanism that draws in the paint, and include a small, shaped orifice through which the paint is discharged. The pumping mechanisms are typically driven by an electric motor, which is operator actuated by a trigger. Airless paint sprayers are capable of pressurizing liquid paint to upwards of 3,000 psi [pounds per square inch] (˜20.7 MPa). Due to these high pressures, paint sprayers often include a relief valve positioned between the pumping mechanism and the discharge orifice. 
     A conventional relief valve comprises a simple spring-biased valve that opens at an overpressure condition. Additionally, the valve can be manually actuated to prime the pumping mechanism and to relieve pressure and drain paint after operation is completed. 
     Some airless sprayers have complex, separate pressure control devices, such as an electronic transducer, a bourdon tube, or a spring-loaded pressure-actuated piston, to activate an electrical switch to turn on/off the motor. For example, fluid delivery systems have been outfitted with Bourdon tubes to provide a visual indication of pressure. In other designs, a bourdon tube, or other pressure transducer, is provided that automatically turns the drive motor off when a threshold pressure level is exceeded, such as described in U.S. Pat. No. 5,292,232 to Krohn et al, which is assigned to Graco Inc. Spraying is thus interrupted while pressure within the system rebalances as the motor turns off and on, resulting in varying system pressure, potentially diminishing the quality of the sprayed finish. There is, therefore, a need for improving control over spray parameters in airless sprayers; in particular, one providing essentially continuous control of pressure without costly and/or complex components, and light in weight for hand-held applications. 
     SUMMARY 
     The present invention is directed to a control valve for a fluid dispensing device. The control valve comprises an elongate valve stem, a valve body, a cap and an adjustment mechanism. The elongate valve stem has a flange. The valve body comprises a valve bore in which the elongate valve stem is configured to translate, and a flow path intersecting the valve bore and into which the valve stem penetrates. The cap is joined to the valve body to receive the valve stem such that the flange is positioned between the valve body and the cap. The adjustment mechanism changes a position of the cap with respect to the valve body to vary a distance between the cap and the flange which adjusts the spring force, and thereby the pressure at which the valve opens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of the main components of an airless fluid dispensing device in which a control valve of the present invention may be used. 
         FIG. 2  shows a side perspective view of a handheld sprayer embodiment of the dispensing device of  FIG. 1  including a control valve of the present invention. 
         FIG. 3  shows an exploded view of the handheld sprayer of  FIG. 2 , showing a housing, a spray tip assembly, a fluid cup, a pumping mechanism, a drive element and the control valve. 
         FIG. 4  shows an exploded view of the pumping mechanism and drive element of  FIG. 3 . 
         FIG. 5  shows a cross-sectional view of an assembled pumping mechanism and drive element. 
         FIG. 6  shows a cross-sectional view of a control valve used in the pumping mechanism of  FIGS. 3-5 . 
         FIG. 7A  shows an exploded view of the control valve of  FIGS. 2-6  from an exterior perspective. 
         FIG. 7B  shows an exploded view of the control valve of  FIGS. 2-6  from an interior perspective. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a block diagram of portable airless fluid dispensing device  10  in which the control valve of the present invention may be used. In the embodiment shown, device  10  comprises a portable airless spray gun comprising housing  12 , spray tip assembly  14 , fluid container  16 , pumping mechanism  18 , drive element  20  and control valve  22 . In various embodiments of the invention, spray tip assembly  14 , fluid container  16 , pumping mechanism  18 , drive element  20  and control valve  22  are packaged together in a portable spraying system. For example, spray tip assembly  14 , fluid container  16 , pumping mechanism  18 , drive element  20  and control valve  22  can each be mounted directly to housing  12  to comprise an integrated handheld device, as described with respect to  FIGS. 2 and 3 . However, in other embodiments, any type of spraying system may be used with control valve  22 . 
     Spray gun  10  comprises an airless dispensing system in which pumping mechanism  18  draws fluid from container  16  and, with power from drive element  20 , pressurizes the fluid for atomization through spray tip assembly  14 . Pumping mechanism  18  comprises, in different embodiments, a gear pump, a piston pump, a plunger pump, a vane pump, a rolling diaphragm pump, a ball pump, a rotary lobe pump, a diaphragm pump or a servo motor having a rack and pinion drive. Drive element  20  comprises, in different embodiments, an electric motor, an air-driven motor, a linear actuator or a gas engine which can be used to drive a crankshaft, cams, a wobble plate or rocker arms. In various embodiments, pumping mechanism  18  generates orifice spray pressure, or running pressure, from about 360 pounds per square inch [psi] (˜2.48 MPa) up to about 3,000 psi (˜20.7 MPa), or higher. Control valve  22  of the present invention permits an operator to adjust pressures and flow rates generated by pumping mechanism  18  independent of the speed of pumping mechanism  18 . 
       FIG. 2  shows a side perspective view of spray gun  10  having housing  12 , spray tip assembly  14 , fluid container  16 , pumping mechanism  18  ( FIG. 3 ), drive element  20  ( FIG. 3 ) and control valve  22 . Control valve  22  includes lever  23  and knob  24 . Spray gun  10  also includes trigger  25  and battery  26 . Spray tip assembly  14  includes guard  28 , spray tip  30  and connector  32 . Drive element  20  and pumping mechanism  18  are disposed within housing  12 . Housing  12  includes integrated handle  34 , container lid  36  and battery port  38 . 
     Fluid container  16  is provided with a fluid that is desired to be sprayed from spray gun  10 . For example, fluid container  16  is filled with a paint or varnish that is fed to spray tip assembly  14  through coupling with lid  36 . Battery  26  is plugged into battery port  38  to provide power to drive element  20  within housing  12 . Trigger  25  is connected to battery  26  and drive element  20  such that upon actuation of trigger  25  a power input is provided to pumping mechanism  18 . Pumping mechanism  18  draws fluid from container  16  and provides pressurized fluid to spray tip assembly  14 . Connector  32  couples spray tip assembly  14  to pump  18 . Tip guard  28  is connected to connector  32  to prevent objects from contacting high velocity output of fluid from spray tip  30 . Spray tip  30  is inserted through bores within tip guard  28  and connector  32  and includes a spray orifice that receives pressurized fluid from pumping mechanism  18 . Spray tip assembly  14  provides a highly atomized flow of fluid to produce a high quality finish. Control valve  22  of the present invention permits an operator to, among other things, open pumping mechanism  18  to atmospheric pressure using lever  23 , and adjust the maximum spray pressure of spray gun  10  using knob  24 . 
       FIG. 3  shows an exploded view of spray gun  10  having housing  12 , spray tip assembly  14 , fluid container  16 , pumping mechanism  18 , drive element  20  and control valve  22 . Spray gun  10  also includes trigger  25 , battery  26 , clip  40 , switch  42  and circuit board  44 . Spray tip assembly  14  includes guard  28 , spray tip  30 , connector  32  and barrel  46 . Pumping mechanism  18  includes suction tube  48 , return line  50  and valve  52 . Drive element  20  includes motor  54 , gearing assembly  56  and wobble drive assembly  58 . Housing  12  includes integrated handle  34 , container lid  36  and battery port  38 . 
     Pumping mechanism  18 , drive element  20 , gearing  56 , wobble drive assembly  58  and valve  52  are mounted within housing  12  and supported by various brackets. For example, gearing  56  and wobble drive assembly  58  include bracket  60  which connects to housing  62  of pumping mechanism  18  using fasteners  64 . Valve  52  is threaded into housing  62 , and connector  32  of spray tip  30  is threaded onto valve  52 . Spray tip  30 , valve  52 , pumping mechanism  18  and drive element  54  are supported within housing  12  by ribs  66 . Switch  42  is positioned above handle  34  and circuit board  44  is positioned below handle  34  such that trigger  25  is ergonomically positioned on housing  12 . Switch  42  includes terminals for connecting with drive element  20 , and battery  26  is supported by port  38  of housing  12  in such a manner so as to connect with circuit board  44 . Battery  26  may comprise a Lithium battery, a Nickel battery, a Lithium-ion battery or any other suitable rechargeable battery. In one embodiment, battery  26  comprises a 18 VDC battery, although other lower or higher voltage batteries can also be used. Fluid container  16  is threaded into lid  36  of housing  12 . Suction tube  48  and return line  50  extend from pumping mechanism  18  into fluid container  16 . Clip  40  allows gun  10  to be conveniently stowed such as on a belt of an operator or a storage rack. 
     To operate spray gun  10 , fluid container  16  is filled with a liquid to be sprayed from spray tip  30 . Trigger  25  is actuated by an operator to activate drive element  20 . Drive element  20  draws power from battery  26  and causes rotation of a shaft connected to gearing  56 . Gearing  56  causes wobble drive  58  to provide an actuation motion to pumping mechanism  18 . Pumping mechanism  18  draws liquid from container  16  using suction tube  48 . Air in the pump, or fluid flow greater than needed, is returned to container  16  through control valve  22  and return line  50 . Pressurized liquid from pumping mechanism  18  is provided to valve  52 . Once a threshold pressure level is achieved, valve  52  opens to allow pressurized liquid into barrel  46  of spray tip  30 . Barrel  46  includes a spray orifice that atomizes the pressurized liquid as the liquid leaves spray tip  30  and gun  10 . Barrel  46  may comprise either a removable spray tip that can be removed from tip guard  28 , or a reversible spray tip that rotates within tip guard  28 . Control valve  22  is inserted through access flange  67  and connected to pumping mechanism  18  to provide 1) a priming valve, 2) a rapid depressurization valve, 3) a safety valve and 4) a pressure adjustment valve. 
       FIG. 4  shows an exploded view of pumping mechanism  18  and drive element  20  of  FIG. 3 . Pumping mechanism  18  includes housing  62 , fasteners  64 , inlet valve assembly  68 , outlet valve assembly  70 , first piston  72  and second piston  74 . Drive element  20  includes drive shaft  76 , first gear  78 , first bushing  80 , second gear  82 , shaft  84 , first bushing  86 , third bushing  88 , third gear  90 , fourth bushing  92  and fourth gear  94 . Wobble drive mechanism  58  includes connecting rod  96 , bearing  98 , rod  100  and sleeve  102 . First piston  72  includes first piston sleeve  104  and first piston seal  106 . Second piston  74  includes second piston sleeve  108  and second piston seal  110 . Inlet valve  68  includes inlet valve cartridge  112 , seal  114 , seal  116 , inlet poppet valve  118  and inlet spring  120 . Outlet valve  70  includes outlet valve cartridge  122 , seat  124 , outlet poppet valve  126  and outlet spring  128 . 
     Drive shaft  76  is inserted into bushing  80  such that gear  78  rotates when drive element  20  is activated. Bushings  86  and  88  are inserted into a receiving bore within bracket  60 , and shaft  84  is inserted into bushings  86  and  88 . Gear  82  is connected to a first end of shaft  84  to mesh with gear  78 , and gear  90  is connected with a second end of shaft  84  to mesh with gear  94 . Sleeve  102  is inserted into a receiving bore within housing  62  and rod  100  is inserted into sleeve  102  to support wobble drive mechanism  58 . Bearing  98  connects rod  100  to connecting rod  96 . Connecting rod  96 , which comprises a ring with a stud, couples with first piston  72 . First piston  72  and second piston  74  are inserted into piston sleeves  104  and  108 , respectively, which are mounted within pumping chambers within housing  62 . Valve seals  106  and  110  and sleeves  104  and  108  seal the pumping chambers. Fasteners  64  are inserted through bores in housing  62  and bushings  130  and threaded into housing  60 . Inlet valve cartridge  112  is inserted into a receiving bore in bracket  62 . Inlet spring  120  biases poppet valve  118  against cartridge  112 . Similarly, outlet valve cartridge  122  is inserted into a receiving bore in housing  62  such that outlet spring  128  biases poppet valve  126  against seat  124 . Seals  114  and  116  prevent fluid from leaking out of valve  68 , and seat  124  prevents fluid from leaking out of valve  70 . Control valve  22  is inserted into receiving bore  132  in housing  62  to intersect fluid flow from pistons  72  and  74  and to intersect vent  133 . Vent  133  can be positioned on an underside of housing  62  for coupling to return line  50  as shown in  FIG. 3 . Control valve  22  is adjustable to permit an operator to manually set the maximum pressure that will be generated within pumping mechanism  18 . 
       FIG. 5  shows a cross-sectional view of pumping mechanism  18  assembled with drive element  20 . Drive element  20  comprises a mechanism or motor for producing rotation of drive shaft  76 . In the embodiment shown, drive element  20  comprises a DC (direct current) motor that receives electrical input from battery  26 , or another electrical power source. In other embodiments, drive element comprises an AC (alternating current) motor that receives electrical input from a power outlet or a pneumatic motor that receives compressed air as an input. Pumping mechanism  18  comprises a dual piston pump. In other embodiments, pumping mechanism  18  may comprise a double-displacement single piston pump, a gerotor (generated rotor), a gear pump or a rotary vane pump. 
     First gear  78  is fit over drive shaft  76  and is held in place by bushing  80 . Bushing  80  is secured to shaft  76  using a setscrew or another suitable means. First gear  78  meshes with second gear  82 , which is connected to shaft  84 . Shaft  84  is supported in bracket  60  by bushings  86  and  88 . Gear  90  is disposed on a reduced diameter portion of shaft  84  and secured in place using bushing  92 . Bushing  92  is secured to shaft  84  using a setscrew or another suitable means. Gear  90  meshes with gear  94  to rotate rod  100 . Rod  100  is supported by sleeve  102  and bushing  134  in housings  62  and  60 , respectively. Gears  78 ,  82 ,  90  and  94  provide a gear reduction means that slows the input to rod  100  from the input provided by drive element  20 . 
     Rotation of rod  100  produces linear motion of ball  138  of connecting rod  96  through wobble of hub  139 . Ball  138  is mechanically connected to socket  140  of piston  72 . Thus, connecting rod  96  directly actuates piston  72  in both advanced and retracted positions. Piston  72  advances and retracts within piston sleeve  104  in housing  62 . As piston  72  retreats from the advanced position, fluid is drawn into valve  68 . Valve  68  includes stem  142  to which suction tube  48  connects. Suction tube  48  is submerged within a liquid inside fluid container  16  ( FIG. 3 ). The liquid is drawn into pumping chamber  144  around poppet valve  118  and through inlet  146 . Poppet valve  118  is biased against valve cartridge  112  by spring  120 . Seal  116  prevents fluid from passing between cartridge  112  and poppet valve  118  when poppet valve  118  is closed. Seal  114  prevents fluid from passing between cartridge  112  and housing  62 . Valve stem  118  is drawn away from cartridge  112  by suction produced by piston  72 . As piston  72  advances, fluid within pumping chamber  144  is pushed through outlet  148  toward valve  70 . 
     Fluid pressurized in chamber  144  is pushed into pressure chamber  150  around poppet valve  126  of valve  70 . Poppet valve  126  is biased against seat  124  by spring  128 . Seat  124  prevents fluid from passing between poppet valve  126  and housing  62  when valve  126  is closed. Poppet valve  126  is forced away from housing  62  as piston  72  moves toward the advanced position, as spring  120  and the pressure generated by piston  72  closes valve  68 . Pressurized fluid from pumping chamber  144  fills pressure chamber  150 , comprising the space between cartridge  122  and housing  62 , and pumping chamber  152 . The pressurized fluid also forces piston  74  to the retracted position. The volume displaced by the advance of piston  72  is larger than the displacement of piston  74 . As such, a single stroke of piston  72  provides enough fluid to fill pumping chamber  152  and maintain pressure chamber  150  filled with pressurized fluid. Additionally, piston  72  has a large enough volume to push pressurized fluid through outlet  154  of housing  62 . 
     As piston  72  retreats to draw additional fluid into pumping chamber  144 , piston  74  is pushed forward by connecting rod  96 . Piston  74  is disposed within piston sleeve  108  in housing  62 , and piston seal  110  prevents pressurized fluid from escaping pumping chamber  152 . Piston  74  advances to evacuate fluid pushed into pumping chamber  152  by piston  72 . The fluid is pushed back into pressure chamber  150  and through outlet  154  of housing  62 , but is prevented by valve  70  from entering chamber  148 . Piston  72  and piston  74  operate out of phase with each other. For the specific embodiment shown, piston  74  is one-hundred eighty degrees out of phase with piston  72  such that when piston  74  is at its most advanced position, piston  72  is at its most retracted position. Operating out of phase, pistons  72  and  74  operate in synch to provide a continuous flow of pressurized liquid to pressure chamber  150  while also reducing vibration in spray gun  10 . Pressure chamber  150  acts somewhat as an accumulator to provide a more constant flow of pressurized fluid to outlet  154  such that a continuous flow of liquid can be provided to valve  52  and spray tip assembly  14  ( FIG. 3 ). Receiving bore  132  ( FIG. 4 ) of housing  62  extends to intersect pressure chamber  150 . Control valve  22  is inserted in receiving bore  132  and is configured to automatically open when pressures generated by pumping mechanism  18  in pressure chamber  150  exceed a threshold level set by control valve  22  or when manually actuated. 
       FIG. 6  shows a cross-sectional view of control valve  22  used in pumping mechanism  18  of  FIGS. 3-5 . Control valve  22  includes housing  202 , plunger  204 , spring  206 , cap  208 , ball  210 , gasket  212 , seat  213 , O-ring seal  214  and backup ring  215 . Body  202  comprises base  216 , cup  218 , spring bore  219 , inlet bore  220 , stem bore  221 , outlet bore  222  and body threads  224 . Plunger  204  comprises flange  228 , stem  229  with non-conductive coating  229 A, seal seat  230 , ball guide  232  and lever bore  234 . Cap  208  comprises cap threads  235 , outer sleeve  236 , scalloped rim  238 , inner sleeve  240 , which defines valve bore  242 , and end wall  244 . 
     Using body threads  224 , annular valve body  202  is threaded into receiving bore  132  ( FIG. 4 ) of housing  62  to intersect pressure chamber  150  ( FIG. 5 ). Inlet bore  220  is fluidly coupled to pressure chamber  150  and is therefore exposed to the fluid pressure generated by pumping mechanism  18 . Outlet bore  222  extends through body  202  to align with a vent, such as vent  133 , in housing  62  to receive return line  50  ( FIG. 3 ), which extends into fluid container  16  ( FIG. 3 ). As such, a complete circuit is formed between fluid container  16 , suction tube  48 , pumping mechanism  18 , pressure chamber  150 , relief valve  22  and return line  50 . 
     Plunger  204  is inserted into stem bore  221  through cup  218  such that flange  228  is disposed within spring bore  219  and stem  229  extends through and out of cup  218 . Spring bore  219  comprises a larger diameter extension of stem bore  221 . Seat  213  is disposed between housing  62  and body  202  within inlet bore  220 . Gasket  212  is pushed into inlet bore  220  to maintain assembly of seat  213  and ball  210  within valve body  202 . When control valve  22  is fully assembled, ball guide  232  of plunger  204  holds ball  210  against seat  213  to prevent fluid from pressure chamber  150  from passing through inlet bore  220  and into outlet bore  222 . O-ring seal  214  is positioned within seal seat  230  between body  202  and plunger  204  to prevent fluid within bore  222  from entering bore  219  when plunger  204  is retraced from seat  213 . Backup ring  215 , which comprises a split ring or washer, is positioned around valve stem  229  to prevent extrusion of o-ring  214  into stem bore  221 . Spring  206  is positioned within bore  219  to push against flange  228  and cap  208 . Cap threads  235  on outer sleeve  236  of cap  208  are threaded into bore  219  on cup  218  such that stem  229  extends into inner sleeve  240  and through end wall  244 . Cap  208  comprises a spring retainer that puts spring  206  in compression to bias plunger  204  toward seat  213  and housing  62 . As discussed below, knob  24  and lever  23  (shown in  FIGS. 2 ,  7 A and  7 B) are slipped over valve stem  229 . Knob  24  engages scalloped rim  238  and lever  23  couples to lever bore  234 . 
     Valve  22  provides priming means for pumping mechanism  18 . Upon initiating a new use of spray gun  10 , before fluid has filled pumping mechanism  18 , it is necessary to purge air from within spray gun  10  before buildup of pressure is possible. Lever  23  ( FIG. 1 ;  FIGS. 7A &amp; 7B ), which is connected to stem  204  by a pin at bore  234 , can be pushed or pulled by an operator to withdraw plunger away from seat  212  via cam action with face  252  which causes ball  210  to disengage from seat  213 . Thus, upon activation of pumping mechanism  18 , air from within spray gun  10  is displaced by fluid from container  16  and purged from spray gun  10  through vent  133 . Likewise, as fluid begins to flow from container  16 , control valve  22  re-circulates the fluid back to container  16 . When lever  23  is released, valve  52  ( FIG. 3 ) will open upon appropriate fluid pressure to keep fluid pressure to spray tip  14  consistent. 
     Valve  22  also provides a means for rapidly depressurizing spray gun  10  after use. For example, after operation of spray gun  10  when drive element  20  has ceased operating pumping mechanism  18 , pressurized fluid remains within spray gun  10 . It is, however, desirable to depressurize spray gun  10  such that spray gun  10  can be disassembled and cleaned. Thus, displacement of lever  23  opens valve  22  to drain pressurized fluid within pumping mechanism to container  16  and to release any stored potential energy within spray gun  10 . 
     Valve  22  also comprises a safety valve to prevent pumping mechanism  18  from becoming over-pressurized. Depending on the preload setting of spring  206 , plunger  204  will be displaced when pressure within pressure chamber  150  reaches a desired threshold level. At such level, pressure chamber  150  is fluidly connected to bore  222  to allow liquid within pressure chamber  150  to travel into vent  133 . Thus, the liquid is returned to container  16  and can be recycled by pumping mechanism  18 . 
     Notably, this response also allows the valve to be used as a control for the spraying pressure delivered to tip  14 . Here, cap  208  of valve  22  comprises an adjustment mechanism that permits variation of the compression induced in spring  206 , thereby changing the maximum pressure that can be generated by pumping mechanism  18 . In the embodiment shown, cap threads  235  on outer sleeve  236  engage internal threads on cup  218  to permit cap  208  to be rotated to adjust its position relative to base  216  and flange  228 . In other embodiments, other mechanisms can be used, such as a bimodal button mechanism that adjusts the compression of spring  206  between two settings. In one embodiment, valve  22  can be configured to open up anywhere between 1,000 psi (˜6.9 MPa) and 3,000 psi (˜20.7 MPa). In the described embodiment, knob  24  ( FIG. 1 ; FIGS.  7 A &amp;  7 B) is adjusted to rotate outer sleeve  236  within cup  218  to adjust the spring compression. 
       FIG. 7A  shows an exploded view of control valve  22  of  FIGS. 2-6  from an exterior perspective.  FIG. 7B  shows an exploded view of control valve  22  of  FIGS. 2-6  from an interior perspective.  FIGS. 7A and 7B  are discussed concurrently. Control valve  22  comprises body  202 , plunger  204 , spring  206 , cap  208 , ball  210 , gasket  212 , seat  213 , O-ring seal  214  and backup ring  215 . Body  202  comprises base  216 , cup  218 , spring bore  219 , inlet bore  220 , outlet bore  222  and body threads  224 . Plunger  204  comprises flange  228 , stem  229 , seal seat  230  and lever bore  234 . Cap  208  comprises cap threads  235 , outer sleeve  236 , scalloped rim  238 , inner sleeve  240 , which defines valve bore  242 , and end wall  244 . Knob  24  comprises end face  252 , stem bore  254 , scalloped ring  256 , pliable fingers  258  and dial  260 . Dial  260  includes grips  262  and indicator  264 . Valve body  202  includes faceted surface  266 . 
     Outer sleeve  236  of cap  208  is threaded into cup  218  of valve body  202 . Knob  24  is coupled to cap  208  via a spline connection that permits relative axial movement, but that prevents relative rotational movement. Specifically, scalloped ring  256  of end face  252  slide into engagement with scalloped rim  238  of cap  208 . As such, knob  24  is locked into circumferential engagement with cap  208 . With ring  256  and rim  238  engaged, pliable fingers  258  are pushed across cup  218  and over faceted surface  266 . Pliable fingers  258  deflect radially outwardly to hug the radially outer perimeter of faceted surface  266 . However, sufficient force can be used to overcome the force of pliable fingers  258  to rotate fingers  258  circumferentially across surface  266 , or to remove knob  24  axially from cap  208 . Specifically, pliable fingers  258  can be situated into a plurality of preset positions along faceted surface  266 , as discussed below. Axial movement of knob  24  is limited by the retention of the pin  270  and lever  23 . 
     Pliable fingers  258  provide tactile indications of the position of cap  208  such that an operator can move knob  24  in even increments. In the embodiment shown, faceted surface  266  comprises a hexagonal cross-sectional area providing six flat surfaces and six edges against which pliable fingers  258  engage. Specifically, the interior facing surfaces of pliable fingers  258  include crenellations that are shaped to engage the edges of faceted surface  266 . In the embodiment shown, eight pliable fingers  258  include sixteen crenellations plus an additional eight spaces between the fingers that produce a total of twenty-four positions of pliable fingers  258  relative to faceted surface  266 . In such an embodiment, however, knob  24  is restricted to rotating 270 degrees such that eighteen adjustments, thus, nineteen positions are provided. Indicator  264  provides a visual indication to an operator of the position of cap  208  relative to valve body  202 . Indications can be provided on housing  12  ( FIG. 1 ) to provide a visual representation of the position of knob  24 , of pressure or of flow. 
     With ring  256  and rim  238  fully seated, the shoulders in tabs  268  abut the end of cup  218  to provide a solid base for the actuation of lever  23 . Spring  206  is compressed between flange  228  and end wall  244  to push ball  210  into seat  213  in inlet bore  220 . Valve stem  229  extends through valve bore  242  on cap  208  and bore  254  on knob  24 , and pin  270  is used to secure lever  23  at bore  234 . Dial  260  of knob  24  is spaced from pliable fingers  258  to permit access flange  67  ( FIG. 3 ) from housing  12  to be inserted therebetween to provide a coarse seal. 
     As discussed above, outer sleeve  236  of cap  208  can be rotated to adjust the engagement of external threads  235  with internal threads of cup  218 . Unscrewing of cap  208  retracts end wall  244  away from flange  228  and base  216 , thereby relieving compression of spring  206 . Dial  260 , through the scalloped engagement of rim  238  and ring  256 , is provided for an operator to easily rotate cap  208 . Specifically, dial  260  includes grips  262  to enable knob  24  to be easily rotated, such as when wet. When knob  24  is rotated such that cap  208  is fully threaded into cup  218 , spring  206  is compressed to its maximum level. As such, a greater amount of pressure must be generated within pressure chamber  150  to open control valve  22 . When knob  24  is rotated such that cap  208  is fully retreated from cup  218 , spring  206  is compressed to its minimum level. As such, a lesser amount of pressure must be generated within pressure chamber  150  to open control valve  22 . Any pressure generated within pressure chamber  150  greater than the force generated by spring  206 , will retract ball  210  away from seat  213 , causing fluid to pass through vent  133  and into return line  50  and fluid container  16 . Thus, spraying from spray gun  10  can continue without interruption below the threshold level determined by control valve  22 . At the minimum level, more fluid will be recycled to container  16  then at the maximum level for any given over-pressure condition. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. For example, there are other ways knob  24  could be elastically held so it provides tactile feedback to the person adjusting control valve  24 , and to help knob  24  resist inadvertent repositioning, including features which provide interaction with sprayer housing  12 . Also, the scallops of knob  24  and cap  208  work together such that rotations of knob  24  are translated to cap  208 . This radial connection between these parts could instead be axial features, such as pins and sockets; matching and opposing pins, cogs, dogs; matching radiating facets; etc. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.