R. h. dual media filter

Claim 2

A filter in accordance with claim 1 wherein said coarse-granulation bed consists of gravel of grain size 1.5 to 6 mm and said fine-granulation bed consists of filtering sand having a grain size of about 0.6 - 1.3.

Claim 3

A filter in accordance with claim 1 further comprising means for conducting backwash water and air after passing through said fine-granulation bed to said coarse-granulation bed, and means for conducting additional backwash water and air to said coarse-granulation bed whereby a greater quantity of backwash per square foot of bed area can pass through said coarse-granulation bed than said fine-granulation bed.

Claim 4

A filter in accordance with claim 4 further comprising pipe means passing through said fine-granulation bed connecting said space above said fine-granulation bed to the space below said coarse-granulation bed; whereby an additional portion of backwash water and air can be conducted directly to said coarse-granulation bed without passing through said fine-granulation bed so that a greater quantity of backwash can pass through said coarse-granulation bed than through said fine-granulation bed.

Claim 5

A filter in accordance with claim 15 wherein the depth of said fine-granulation bed is greater than the depth of said coarse granulation bed.

Claim 6

A filter in accordance with claim 6 wherein said first draining device is located within said fine-granulation bed and means to feed pre-filtered water from said coarse-granulation bed simultaneously to the upper and lower surfaces of said fine-granulation bed whereby the water to be filtered flows in counterflow downwardly through the upper portion of said fine-granulation bed and upwardly through the lower portion of said bed to said first draining device.

Claim 7

A filter in accordance with claim 2 wherein said fine-granulation bed has an upper surface approximately twice as great as the upper surface of said coarse-granulation bed.

Claim 8

A filter in accordance with claim 8 wherein said coarse-granulation bed and said fine-granulation bed are side-by-side within said housing.

Claim 9

A filter adapted for filtering water and subsequent back washing with water and air comprising: a horizontally extending housing; a coarse-granulation bed in said housing located at one side of said housing, means to support said coarse-granulation bed, having a space therebeneath, said coarse-granulation bed having a space thereabove extending to the top of said housing; a fine granulation bed in said housing located at the other side of said housing, said fine granulation bed having a greater surface area than said coarse granulation bed, means to support said fine-granulation bed having a space therebeneath, said fine granulation bed having a space thereabove extending to the top of said housing; a first vertical plate extending downwardly from the top of said housing to a point slightly above the bottom thereof below said coarse-granulation bed support means, said plate forming the inner side wall of said coarse granulation bed; a second vertical plate extending upwardly from the bottom of said housing to a point slightly below the top thereof and above said fine granulation bed upper surface, said plate forming the inner side wall of said fine granulation bed; said first and second vertical plates being separated from one another to form a passageway area therebetween connecting a space below said coarse granulation bed with a space above said fine granulation bed; and inlets and outlets above said coarse granulation bed and below said fine granulation bed.

Claim 10

A filter in accordance with claim 10 wherein the position of said first and second vertical plates are adjustable whereby the relative surface areas of said coarse and fine granulation beds can be controlled.

Claim 11

A process for filtering raw water comprising passing said raw water downwardly through a coarse-granulation bed of a filter and thence through a separate fine-granulation bed of said filter, continuing said passing of raw water through the filter until backwashing is required, then stopping the passing of raw water, passing backwash water and air first through said fine-granulation bed and thence upwardly through said coarse-granulation bed, and passing an additional amount of air only through said coarse-granulation bed.

Claim 12

A process according to claim 12 wherein the water after passage downwardly through said coarse-granulation bed is divided and a first portion is passed downwardly from the upper surface through said fine-granulated bed and a second portion is passed upwardly from the lower surface through said fine-granulation layer with the combined portions of filtered water being removed from a central portion of said fine-granulated bed.

Claim 13

A process for filtering a liquid comprising passing said liquid downwardly thru a coarse granulation bed of a filter and thence thru a separate fine-granulation bed of said filter, continuing said passing of liquid through the filter until backwashing is required, then stopping the passing of liquid, passing backwash water and air first upwardly thru said fine-granulation bed and thence upwardly thru said coarse-granulation bed, and passing a greater rate of flow per sq. ft. of bed surface of backwash water and air thru said coarse-granulation bed than thru said fine-granulation bed.

Claim 14

A process for filtering according to claim 14 wherein after the passing of backwash water and air is discontinued, additional rinsing water is passed in the same direction as said backwash, and then the filtration step is started again.

Claim 15

A process for filtering a liquid in a dual filter having a separate coarse granulation bed supported on a plate overlying a separate fine granulation bed supported on a plate comprising passing said liquid downwardly thru said coarse granulation bed to obtain a pre-filtered stream; separating said pre-filtered stream into two parts and passing one part downwardly from the top of said fine granulation bed and the other part upwardly from the bottom of said fine granulation bed; collecting both filtered streams at an intermediate portion of said fine granulation bed and withdrawing it; when backwashing is required, stopping the passing of said liquid; passing backwash water and air upwardly thru said entire fine granulation bed and thence upwardly thru said coarse granulation bed, the rate of flow per sq: ft. of bed surface being maintained greater thru said coarse-granulation bed than thru said fine-granulation bed.

Claim 16

A process for filtering a liquid in a dual filter having a separate coarse granulation bed supported on a plate and fine-granulation bed supported on a plate in side-by-side relationship, comprising passing said liquid downwardly through said coarse granulation bed and thence downwardly through said fine-granulation bed, continuing said passing of liquid thru the filter until backwashing is required, then stopping the passing of said liquid, passing backwash water and air upwardly through said fine-granulation bed and thence upwardly through said coarse-granulation bed, the rate of flow per sq. ft. of bed surface being maintained greater thru said coarse-granulation bed than thru said fine-granulation bed.