apparatus for continuously filtering a flow of melted plastic which includes means for purging the filter without interrupting continuous operation . a filter assembly consists of a trap plate and breaker plate between which filters are disposed . the trap and breaker plates each defines triangularly shaped openings diposed in a circular array , each of which is subdivided into smaller passages for filtering larger contaminants . individual filters also of triangular configuration are sandwiched between registering openings between the trap and breaker plates , each filter consisting of a fine and coarse screen . a collector head is rotatably disposed for selective registration with each of the openings of the trap plate , and an indexing mechanism is included for stepping the collector head for stationary registration with each opening . the collector head communicates with a contaminant discharge passage that is open and closed in timed sequence with movement of the collector head . when the contaminant discharge passage is opened , a part of the filtered plastic downstream of the filter assembly reverses its flow through the opening registering with the collector head , purging the filter screens by carrying collected contaminants . the contaminant - filled flow initially passes into a purge chamber of predetermined volume having a pressurized piston . after a predetermined volume has entered the chamber forcing the piston to retract , a valve breaks communication between the discharge passage and purge chamber , simultaneously establishing communication between the purge chamber and a contaminant discharge outlet , enabling the piston to evacuate the purge chamber and discharge the contaminants .