Rotary Drum Filters (RDF) operate under a high vacuum, rotating a drum into a vat of slurry, dewatering and drying as the drum rotates out of solution and over to the cake discharge side. The filter media is caulked onto the drum and stays in the same place. De-watered and dried filter cake is discharged on the back side using gravity, air blow back, doctor blade or counter-revolving roll. Of these, the doctor blade can cause the most wear on the cloth.

Rotary Vacuum Drum Filters (RVDF) also operate under high vacuum with a drum which rotates in a pan. However, in this design filter, the filter cloth comes off the drum and travels to a discharge system such as a doctor blade, cooch (helix) roll or gravity. After backwash, the cloths return to the pan to repeat the process. The RVDF filter cloth is held on the drum with edge guides using rope, coil springs or molded rubber (PIP) edging. Typical cloth closures are manual sewing, Velcro, clipper lacing or zippers (or a combination of those methods).