Patent ID: 7125434

Claim:
A deep gradient-density filter device having a depth of at least approximately 0.5 inch (1.27 cm.) and capable of filtering a fluid containing a distribution of particles in the range of approximately 25 microns to approximately 0.2 micron, the deep gradient-density filter device comprising in order: (a) a pre-filtration zone comprising layers of filtration material, said pre-filtration zone capable of retaining particles in the range of approximately 25 microns to approximately 1 micron, (b) a primary filtration zone comprising filtration material, said primary filtration zone capable retaining particles in the range of approximately 1 micron to approximately 0.3 micron, and (c) a polishing zone comprising layers of filtration material, said polishing zone capable of retaining particles in the range of approximately 0.3 micron to approximately 0.2 micron; and wherein the retention capabilities of the pre-filtration zone, the primary filtration zone, and the polishing zone, as recited in (a), (b), and (c) respectively, are established at a fluid velocity of at least approximately 100 cm/hr and an initial hydraulic permeability of greater than approximately 10 cm/hr/psi.