Automatically backwashed gravity filter

Claim 2

In an automatically backwashed gravity filter including: a filter compartment containing a bed of filter media, a fluid inlet conduit vented to the atmosphere and connected to the filter compartment, an underdrain beneath the bed of filter media, a backwash storage compartment located at a higher elevation than the bed of filter media and connected to the underdrain by an open conduit, whereby filtered fluid accumulates in the backwash storage compartment, and means for initiating a backwash cycle when the inlet pressure in the filter compartment reaches a certain level; the improvement comprising: sensing means positioned on said backwash storage compartment for detecting changes in the fluid level in said backwash storage compartment, and means responsive to said sensinG means for increasing the rate at which unfiltered fluid is supplied to said fluid inlet conduit as the fluid level in said backwash storage compartment drops and decreasing the rate at which unfiltered fluid is supplied to said fluid inlet conduit as the fluid level in the backwash storage compartment rises.

Claim 3

A filter according to claim 1 wherein the sensing means for detecting changes in the fluid level in the backwash storage compartment comprises an automatic level controller.

Claim 4

A filter according to claim 2 wherein the means for increasing and decreasing the rate at which unfiltered fluid is supplied comprises an automatic control valve and means for opening and closing the valve in response to signals from the automatic level controller.

Claim 5

A filter according to claim 1 further comprising an outlet conduit through which filtered water is discharged while the backwash storage compartment is being filled.

Claim 6

In an automatically backwashed gravity filter including a filter compartment containing a bed of filter media, a fluid inlet conduit vented to the atmosphere and connected to the filter compartment, an underdrain beneath the bed of filter media, a backwash storage compartment located at a higher elevation than the bed of filter media and connected to the underdrain by an open conduit, whereby filtered fluid accumulates in the backwash storage compartment, a clearwell storage tank, and means for initiating a backwash cycle when the inlet pressure in the filter compartment reaches a certain level; the improvement comprising: an outlet conduit connected to said backwash storage compartment below the upper fluid level in said backwash storage compartment and connected to said clearwell storage tank below the upper fluid level in said clearwell storage tank; sensing means positioned on said clearwell storage tank above said outlet conduit for detecting changes in the fluid level in said clearwell storage tank and in said backwash storage compartment; and means responsive to said sensing means for increasing the rate at which unfiltered fluid is supplied to said fluid inlet conduit as the fluid level in said backwash storage compartment drops and decreasing the rate at which unfiltered fluid is supplied to said fluid inlet conduit as the fluid level in the backwash storage compartment rises.

Claim 7

In an automatically backwashed gravity filter including a filter compartment containing a bed of filter media, a fluid inlet conduit vented to the atmosphere and connected to the filter compartment, an underdrain beneath the bed of filter media, a backwash storage compartment located at a higher elevation than the bed of filter media and connected to the underdrain by an open conduit, whereby filtered fluid accumulates in the backwash storage compartment, a clearwell storage tank, and means for initiating a backwash cycle when the inlet pressure in the filter compartment reaches a certain level; the improvement comprising: an outlet conduit connected to said backwash storage compartment below the upper fluid level in said backwash storage compartment and connected to said clearwell storage tank below the upper fluid level in said clearwell storage tank; sensing means positioned on said clearwell storage tank above said outlet conduit for detecting changes in the fluid level in said clearwell storage tank and in said backwash storage compartment; and means responsive to said sensing means for increasing the rate at which unfiltered fluid is supplied to said fluid inlet conduit as the fluid level in said backwash storage compartment drops and decreasing the rate at which unfiltered fluid is supplied to said fluid inlet conduit as the fluid level in the backwash storage compartment rises.

Claim 8

A filter according to claim 5 wherein the sensing means for detecting changes in the fluid level in the clearwell storage tank and the backwash storage compartment comprises an automatic level controller.

Claim 9

A filter according to claim 6 wherein the means for increasing and decreasing the rate at which unfiltered fluid is supplied comprises an automatic control valve and means for opening and closing the valve in response to signals from the automatic level controller.