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 sedrum filterwing, Velcro, clipper lacing or zippers (or a combination of those methods).
In all cases above, the original materials used were woven fabrics, ranging from lightweight multi-filaments to heavy mono-filaments weighing up to 40 oz/yd2 or 1350 g/m2. Depending on the type of filter, the discharge system, the product and the process, a very wide range of textiles have been used in these filters with life varying from a few weeks to multiple years.