an injection molding apparatus which includes a check valve assembly mounted at the forward end of a feed - screw , the valve assembly having forward and rearward valve seat surfaces which co - act in a first position to allow a plasticized polymeric material to enter and flow through the valve into an injection chamber and which co - act in a second position to stop any additional material from entering the valve assembly . the second valve position is effected by a feed - screw injection stroke which generates a back pressure to close the valve , the back pressure moving a check ring of the valve assembly into a position to block entry into the valve . part of the valve seat surfaces are covered with a plurality of ceramic disks and other valve seat surfaces are covered with a metal alloy which effectively increases the abrasion resistance of the valve seat surfaces and thus also increases the wear service life of the check valve assembly . other wear surfaces of the valve assembly may also be coated for abrasion resistance .