This paper addresses the question of the relative amounts of liquid removed during filtration and expression as a function of cake compressibility. As liq uid flows through a porous cake, the accumulative drag collapses the particulate structure, thereby increasing the solid content and displacing the liquid. The use of pump pressure in filtration represents the simplest hydraulic deliquoring process. In expression operations, pistons, membranes, rollers or belts are employed to squeeze the particulate cake after filtration is complete.
Filtration followed by expression at constant pressures ranging from 0.6 to 24.7 MPa (6.1-243.6 atm) was investigated theoretically and experimentally. During filtration and the early stages of expression, the flow rate and average liquid content of highly compressible attapulgite were virtually unaffected by increasing pressure in the range investigated.