Rotary Vacuum Drum Filter (RVDF) Sizing Calculator

In precoat filtration (diatomaceous earth / perlite), as the cake passes into the drying zone, rapid air draw can desiccate compressible cakes, causing deep radial shrinkage cracks. Ambient air immediately short-circuits through the cracks into the drum internal pipes. Drum vacuum drops from 65 kPa to below 15 kPa, stopping filtration instantly across the entire drum submerged zone.

Coarse or heavy mineral slurries ($d_p > 45 ext{ μm}, ho > 2500 ext{ kg/m}^3$) settle within seconds. If the oscillating vat pendulum rake agitator has insufficient sweep or suffers mechanical linkage failure, solids compact into a dense sediment bed at the vat bottom. The rotating drum wedges against the solid bed, stalling the drum drive motor or snapping the circumferential drive chain.

Precoat filters require an automated micrometer knife advance ($10-50 ext{ μm}$ per revolution) to shave off the blinded slime layer. Setting the knife advance rate unnecessarily high burns through an expensive 100 mm precoat bed in 4 hours instead of 16 hours, quadrupling diatomaceous earth consumption costs and wasting thousands of dollars per shift in filter aid.

The stationary rotary vacuum valve on the drum trunnion separates form vacuum, dry vacuum, atmospheric cake discharge, and reverse blow air using sacrificial phenolic or bronze wear plates. Abrasive slurry fines leaking into the valve face score deep grooves across the bridge seals. Compressed blow air leaks directly into the vacuum chambers, destroying cake formation and blowing slurry back into the vat.

When filtering hot saturated slurries (ammonium sulfate, potash, gypsum), the evaporative cooling of air pulled through the cake drops the liquor temperature inside the cloth pores below its saturation limit. Salt crystals nucleate inside the twisted multifilament cloth yarns, petrifying the flexible cloth into an impermeable board that no knife scraper or air blow can clear.