Dispensing gun for mixing and dispensing reactable fluent materials. A cylinder is slidable within a bore in response to a piston sliding within the cylinder. When the cylinder moves away from a discharge opening, orifices in the wall of the cylinder become aligned with supply passages in the bore allowing the reactable fluent materials to mix in the cylinder and be dispensed from the discharge opening. The cylinder, piston and orifices are cleaned by a cleaning solvent at the end of each dispensing operation. Movement of the piston towards the discharge opening draws the cleaning solvent through the orifices into the interior of the cylinder. The dispensing gun is particularly useful for mixing organic resins and polyisocyanates to dispense polyurethane foam.
