In accord with Darcy's law, the flow rate through a porous bed depends upon the pressure drop Δpc. In general, increasing Dpc leads to increased values of flow rate and average percentage solids in filtration operations. When cakes become super-compactible, their behavior undergoes an unexpected change in which both the flow rate and the percentage solids reach maximum values and thereafter are unaffected by increasing Δpc. The critical pressure drop ΔpcR is defined as that value at which the flow rate reaches 90% of its ultimate value. When Δpc is greater than DpcR and is doubled or tripled, the cake resistance approximately doubles or triples leaving the rate virtually unchanged. The super-compactibility problem is analyzed theoretically, and is verified by stepped pressure filtration experiments on different materials from Houston and Korea.

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