a dispensing apparatus is provided for mixing and spraying a and b components of urethane foam plastic whereby urethane foam plastic may be sprayed in place . the gun includes structure whereby a solvent for the a and b components may be readily utilized to thoroughly flush the a and b component valves , the mixing chamber and the mixer for the discharge nozzle and is further constructed in a manner whereby the material handling valves will not be distorted by the materials handled thereby and the gun may be temporarily shutdown for short periods or overnight without the need to turn the flow selectors for the components a and b to the off positions thereof . further , the gun is constructed in a manner whereby the control valves are simultaneously actuatable and the flow selectors and the rotation limiting slots thereof may be lubricated to prevent drying out of the a and b components during an overnight shutdown of the gun preventing the flow selectors from being turned . still further , the gun has been designed in a manner to enhance durability , lessen the need for extensive maintenance and to enhance smoothness of operation .