in line 124 ensures that the mixing chamber valves 46 and 48 will move to the open air supply position in which resin flows from the line 50 and line 56 to the mixer 54 and a curing agent flows from the line 52 and 58 to the mixer 54 prior to the opening of valves 32 and 34 thereby preventing a blocking of the pump discharge before the shifting of the resin supplying mixing chamber valves 46 and 48 a branch line 184 and the shuttle valve 156 operate to connect the air supply to the closing side of the ball valve actuator 150 to close the ball valve 84 and prevent the flow to or from the solvent tank as soon as the valve 115 is moved to the 34 in 34 position in which resin and hardener flow to the mixer 54 valves 132 and 134 lose their air supply and are deactivated so as to prevent the accidental injection of solvent or air into the resin mixture while spraying is in progress the resin and hardening agent are mixed in the static mixer 54 and discharged through the spray nozzles of the spray manifold 60 when spraying is completed or when it is necessary to interrupt the spray operation for any reason valve.