Abstract: A pumping and spraying system for heavy filled viscous primary fluid material comprised of a pump for such materials that will pump the primary fluid without cavitation and a plural component spray gun that will spray the material on demand and automatically divert the heavy filled primary fluid material back to a supply source when a trigger is released. The plural component spray gun is provided with generous size primary fluid conduit passageways through a chamber having a primary fluid valve which controls the flow of the primary fluid to a spray nozzle for delivery with a secondary fluid. An open diversion conduit connected perpendicular to the chamber has smaller passageways that divert the primary fluid back to the supply source whenever the primary fluid valve is closed to control and prevent static back pressure. This permits spraying of a heavy filled viscous primary fluid on demand without separation of the fluid components (i.e. packing-out), or clogging of fluid passageways or the spraying tip.