Drum Filters

Rotary Drum Filters (RDF) operate under a high vacuum, rotating a drum into a “pan” or 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).

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.

BWF's developmental efforts have been in designing and developing needled felts to replace the older technology woven fabrics. As in other liquid filtration processes, the goals remain the same: as high a separation rate as possible while maintaining flow and achieving low solids loss. Although cloth life and durability is secondary to the primary goals, the long life normally achieved by the heavier, more durable felts, is always a plus. Felts also reach equilibrium more rapidly and are able to more readily adapt to changes in process conditions and feed solids.

BWF America has been a leader in the development of unique felts for liquid filtration with variable permeabilities and efficiencies, smooth surfaces for cake release and special treatments to improve overall performance. For an analysis as to which BWF product might meet your needs in liquid filtration, contact your field sales engineer or us directly on the internet.