Spray gun with pressure operated valve

Claim 1

A spray gun comprising a housing, nozzle means on said housing, means for supplying coating material under pressure to said nozzle means, a piston operating in said housing, a coating material valve mounted on an end of said piston within a first cylinder chamber for controlling the flow of such material through said nozzle means, a source of pressure fluid, an additional cylinder in said housing, a differential servo pistonhead connected to said piston at an end opposite to said coating material valve, said piston having an intermediate stem portion thereon sealing but slidably guided in said housing, said differential servo pistonhead being movable in said additional cylinder to perform alternately opening and closing strokes therein under the action of pressure fluid from said source for controlling said coating material valve, said differential servo pistonhead dividing said additional cylinder in a second cylinder chamber around said stem and a third cylinder chamber adjacent to said second cylinder chamber, a passage connected between said second and third cylinder chambers, a one-way valve means arranged in said passage for controlling the flowing of pressure fluid only in the direction from said third cylinder chamber into said second cylinder chamber, means for flowing pressure fluid from said source into said third cylinder chamber and from thence through said one-way valve means into said second cylinder chamber, a maneuvering valve, and means controlled by said maneuvering valve for either supplying pressure fluid from said source to said third chamber for producing said closing stroke of said servo piston head against the action of said pressure fluid in said first and second chambers, or relieving the pressure fluid in said third chamber for releasing said servo piston head for said opening stroke thereof under the action of pressure fluid in said first and second chambers.