The maintenance requirements of the pure gravity filling system are relatively simple. The filler components must be kept clean and well lubricated, and the bearings, bushings, O-rings, and springs must be replaced when they wear excessively. The consistency of the product and the free movement of all moving parts are critical for smooth operation. Underfill may be caused by constriction of the Overflow Port by failure of sufficient product to move into the container during the time period it is under the filler head