Getting excessive good product into the reject container is a common concern of many rotary sieve users. In almost all cases, the problem can be traced back to operational misuse. When a high rate of "overs" occurs, the first place to check is the screen. Is the screen the proper size? Is the screen tensioned correctly? Improper screen size will limit the yield of good product. An improperly tensioned screen will limit passage of good product through the screen. Always refer to your maintenance manual for tips on proper screen tensioning.
Another reason for excessive "overs" can be traced to product over-feed. In normal operation, about two-thirds of the screen area should be used. The additional one-third can handle small product surges. If the feed rate is too high and all of the screen is being used under normal operation, the screen cannot handle the surges, and this additional product is pushed into the "overs" container.