Unloader valve for spray guns

Abstract

An unloader type valve for spray guns supplied from pumps to limit operating pressures of the pump when the spray gun is stopped. The valve utilizes an adjustable spring to select pressure forces for opening the valve and a variable flow passage from the valve to an outlet when the valve is open, the allowing matching of the valve to the precise operating pressures and flow rates in spray gun and pumping system installations. UNLOADER VALVE FOR SPRAY GUNS

I claim: 
     
       1. An unloader valve defined by a hollow valve body having an inlet and an outlet leading to an interior working space in the body, a pressure operated piston movably mounted in the interior space of said body .Iadd.thereby subdividing said interior space into spaces on the opposite sides of said piston.Iaddend., said valve body having a valve seat of smaller cross-sectional area than said piston and formed around said inlet .[.passage.]. , said piston including a reduced portion adapted to engage said seat to close off flow through said body, said valve body including .Iadd.a fluid .Iaddend.passage .[.means.]. .Iadd.defined in said valve body .Iaddend.communicating the space between said seat and said piston, when said piston is away from said seat, with an outlet from said body, .Iadd.said fluid passage being the sole source of fluid communication between said inlet and said outlet, said passage being in communication with a lower face of said piston at one end and an upper face of said piston and said outlet at another end.Iaddend., adjustable means .Iadd.disposed in said passage between said lower face of said piston and said upper face of said piston .Iaddend.for varying the flow area through said passage .[.means.]. .Iadd.thereby providing variable control of the fluid pressures exerted on said faces of said piston under maximum fluid flow through said body.Iaddend., a spring positioned between said piston and an abutment in said valve body to exert closing forces on said piston, and means for adjusting the spring pressure to adjust the closing forces exerted by said spring on said piston to thereby vary the pressure force in said inlet .[.passage.]. necessary to move said piston away from said seat, the entire cross-sectional area of said piston being subjected to the pressure in said space when said piston is away from said seat to thereby hold the piston away from said seat as long as the total force due to pressure in said space exceeds the closing forces of said spring. 
     
     
       2. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 1 wherein said passage .[.means.]. is defined by a passage positioned laterally of said interior .[.space.]. .Iadd.spaces .Iaddend.and communicating with said space on opposite sides of said piston. 
     
     
       3. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 2 wherein said adjustable means for regulating flow is defined by a flow restricting element, and said element is variably positionable across a portion of said passage .[.means.]. by an adjusting screw carried by said body. 
     
     
       4. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 3 wherein said element is variably positionable across a portion of said passage .Iadd., said portion of said passage .Iaddend.extending transversely to the axis of said piston and said passage has a shoulder positioned over said portion and limiting movement of said element over said portion to a position providing a small flow space through said portion. 
     
     
       5. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 1 wherein said means for adjusting spring pressure includes a movable abutment engaging one end of said spring, said abutment being axially movable against said spring by a screw threaded in said body. 
     
     
       6. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 5 wherein said passage .[.means.]. is defined by a passage in said body and positioned laterally of said interior space, said outlet being defined by a bore opening into said .Iadd.interior .Iaddend.space on the side of said piston opposite to the inlet side, said passage communicating with said .Iadd.interior .Iaddend.space by a first bore positioned transversely of said passage and opening into said .[.working.]. .Iadd.interior .Iaddend.space on the inlet side of said piston and a second bore coaxial with said outlet bore and extending transversely of said passage. 
     
     
       7. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 6 wherein said adjustable means for varying the flow area is defined by an element positioned for movement axially of said passage and movable across said second bore to restrict flow therethrough, said valve including means for moving said element and stop means for limiting movement across said second bore to a position leaving a small flow space through said second bore. 
     
     
       8. The .[.structure.]. .Iadd.unloader valve .Iaddend.of claim 7 wherein said stop means is defined by a shoulder in said passage. 
     
     
       9. The .[.structure.].  .Iadd.unloader valve .Iaddend.of claim 7 wherein said means for moving said element is defined by a screw threaded in said body and carrying said element.