US4627923A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus and method of filtering solids from a liquid effluent
Assignee: US Filter Zimpro Inc
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Filing: 1984-09-20
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Granted: 1986-12-09
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Expires: 2004-09-20
Abstract
Abstract There is provided an improvement in a waste effluent filter of the type including a tank, a generally flat fine mesh screen over the lower portion of the tank to define an underdrain cavity below the screen and a filter bed of particulate material having an upper surface and a lower general surface adjacent the underdrain cavity. The particle size of the particulate material being greater than the size of the apertures in the fine mesh screen. The filter improvement includes a jet creating grid for creating a plurality of upwardly directed hydraulic jets evenly distributed throughout the filter bed during the filtering of the effluent through the bed wherein the jet creating grid includes a plurality of nozzles in the bed itself substantially below the upper surface of the bed and above the fine mesh screen a selected distance to retain the lower layer of the bed undisturbed. As a further improvement a plurality of horizontal liquid jets are created as a network over the upper surface of the sand bed to scour the media surface during filtering. A further improvement in the filter is the creation of a plurality of hydraulic cleaning jets usable during backwashing along with a vertical flushing action through the screen from the underdrain cavity. Yet a further improvement in the filter is the provision of a chemical cleaning feature utilizing two separate and distinct chemicals injected into the bed for cleaning the filter bed. Preferably, the chemical injection uses the two sets of vertically displaced jets.
Inventors
- 👤 David S. Ross
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 05:34
CPC Classifications
B; B01; B01D; B01D24/00; B01D24/02; B01D24/20; B01D24/22; B01D24/38; B01D24/40; B01D24/42; B01D24/46; B01D24/4605; B01D24/4621; B01D24/4631; B01D24/4642; B01D24/48; B01D24/4869; B01D2201/00; B01D2201/08; B01D2201/085; B01D2201/44
Claims Analysis
Total Claims: 52
Claim 1
Independent Claim
226 words
Method of operating a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface; a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh elements; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity, said method comprising the steps of: (a) allowing liquid in said tank to increase to a level substantially above said upper surface during filtering; and, (b) during such filtering, periodically regenerating said upper surface by folding filtered material at said upper surface into said filter bed by directing a plurality of evenly distributed hydraulic jets upwardly through said filter bed from a position in said bed and above said flat fine mesh element a given distance whereby a lower filtering layer of said bed remains undisturbed between said jets and said fine mesh element while said upper surface is regenerated.
Claim 2
Dependent Claim
226 words
Method of operating a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface; a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh elements; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity, said method comprising the steps of: (a) allowing liquid in said tank to increase to a level substantially above said upper surface during filtering; and, (b) during such filtering, periodically regenerating said upper surface by folding filtered material at said upper surface into said filter bed by directing a plurality of evenly distributed hydraulic jets upwardly through said filter bed from a position in said bed and above said flat fine mesh element a given distance whereby a lower filtering layer of said bed remains undisturbed between said jets and said fine mesh element while said upper surface is regenerated.
Claim 3
Dependent Claim
31 words
A method of operating a waste effluent filter as defined in claim 1 including the additional step of: (c) periodically directing a plurality of liquid jets horizontally across said upper surface.
Claim 4
Dependent Claim
25 words
A method as defined in claim 2 including the additional step of: (d) repeating steps (a) and (c) during filtering of effluent by said filter.
Claim 5
Dependent Claim
35 words
A method as defined in claim 2 including the additional steps of: (d) sensing a given level of liquid in said tank; and, (e) initiating steps (b) and (c) in response to said sensed level.
Claim 6
Dependent Claim
33 words
A method as defined in claim 1 including the additional steps of: (c) sensing a given level of liquid in said tank; and, (d) initiating step (b) in response to said sensed level.
Claim 7
Dependent Claim
75 words
A method as defined in claim 5 including the additional steps of: (e) sensing a maximum level of liquid above said upper surface; (f) backwashing said filter by forcing liquid through said bed from said lower surface to said upper surface at a rate to fluidize said bed; (g) creating a plurality of hydraulic jets extending from said fine mesh element through said fluidized bed during backwashing whereby said undisturbed layer is agitated during backwashing.
Claim 8
Dependent Claim
260 words
Method of chemically cleaning a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity; said method comprising the steps of: (a) stopping filtering cycle of said filter; (b) forcing a liquid surfactant or wetting agent directly into said bed from a plurality of jets separate from said underdrain; (c) forcing a liquid oxidizing agent directly into said bed from a plurality of jets separate from said underdrain; (d) allowing said bed to soak while said agents react in said bed; (e) directing hydraulic jets upwardly through said filter bed whereby said bed is agitated; (f) expanding said bed by upwardly traveling liquid to create an upper level for said expanded bed; and, (g) overflowing liquid from said tank from above said upper level of said expanded bed as said agents are removed by said upwardly traveling liquid until said agents are substatially removed from said expanded bed.
Claim 9
Dependent Claim
260 words
Method of chemically cleaning a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity; said method comprising the steps of: (a) stopping filtering cycle of said filter; (b) forcing a liquid surfactant or wetting agent directly into said bed from a plurality of jets separate from said underdrain; (c) forcing a liquid oxidizing agent directly into said bed from a plurality of jets separate from said underdrain; (d) allowing said bed to soak while said agents react in said bed; (e) directing hydraulic jets upwardly through said filter bed whereby said bed is agitated; (f) expanding said bed by upwardly traveling liquid to create an upper level for said expanded bed; and, (g) overflowing liquid from said tank from above said upper level of said expanded bed as said agents are removed by said upwardly traveling liquid until said agents are substatially removed from said expanded bed.
Claim 10
Dependent Claim
37 words
A method as defined in claim 7 including the additional step of: (h) blowing a gas upwardly through said filter bed after said bed is expanded and generally before said agents are forced into said filter bed.
Claim 11
Dependent Claim
210 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, backwash means for directing filtered effluent from said underdrain cavity, the improvement comprising: jet creating means for selectively creating a plurality of upwardly directed hydraulic jets evenly distributed throughout said filter bed during filtering of said effluent through said filter bed to regenerate said upper surface periodically, said jet creating means including a plurality of nozzles evenly distributed in said bed, substantially below said upper surface and above said flat fine mesh element a selected distance to retain a lower layer of said bed generally undisturbed during surface regeneration by operation of said hydraulic jets.
Claim 12
Dependent Claim
210 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, backwash means for directing filtered effluent from said underdrain cavity, the improvement comprising: jet creating means for selectively creating a plurality of upwardly directed hydraulic jets evenly distributed throughout said filter bed during filtering of said effluent through said filter bed to regenerate said upper surface periodically, said jet creating means including a plurality of nozzles evenly distributed in said bed, substantially below said upper surface and above said flat fine mesh element a selected distance to retain a lower layer of said bed generally undisturbed during surface regeneration by operation of said hydraulic jets.
Claim 13
Dependent Claim
17 words
The improvement as defined in claim 9 wherein said undisturbed distance is at least about 2.0 inches.
Claim 14
Dependent Claim
38 words
The inprovement as defined in claim 9 wherein said jet creating means includes means for intermittently energizing said hydraulic jets whereby filtered matter on said upper surface is periodically folded into said bed during filtering of said effluent.
Claim 15
Dependent Claim
43 words
The improvement as defined in claim 11 including level sensing means for sensing a preselected level of liquid above said upper surface and means for energizing said jet creating means when the level of said liquid is sensed by said level sensing means.
Claim 16
Dependent Claim
58 words
The improvement as defined in claim 12 including an hydraulic means for creating a plurality of horizontal liquid jets at a given location above said upper surface of said bed and evenly distributed across said bed and means for energizing said hydraulic means when liquid above said filter bed exceeds a given level higher than said given location.
Claim 17
Dependent Claim
58 words
The improvement as defined in claim 9 including an hydraulic means for creating a plurality of horizontal liquid jets at a given location above said upper surface of said bed and evenly distributed across said bed and means for energizing said hydraulic means when liquid above said filter bed exceeds a given level higher than said given location.
Claim 18
Dependent Claim
45 words
The improvement as defined in claim 14 including means for sensing a preselected level of liquid above said upper surface and above said given location and means for energizing said hydraulic means when the level of said liquid is sensed by said level sensing means.
Claim 19
Dependent Claim
42 words
The improvement as defined in claim 14 including level sensing means for sensing a predetermined level of liquid above said upper surface and control means for intermittently energizing said jet creating means and said hydraulic means when said predetermined level is sensed.
Claim 20
Dependent Claim
60 words
The improvement as defined in claim 14 including backwash means for forcing filtered liquid into said underdrain cavity, through said fine mesh element, through said filter bed from said lower surface to said upper surface at a flow rate sufficient to expand said filter bed to provide said bed with a second expanded upper level and then from said tank.
Claim 21
Dependent Claim
37 words
The improvement as defined in claim 17 including means for actuating said hydraulic means during operation of said backwashing means and means for locating said hydraulic means to create said horizontal jets above said expanded upper level.
Claim 22
Dependent Claim
56 words
The improvement as defined in claim 17 including means below, but at, said fine mesh element for creating a plurality of evenly distributed hydraulic cleaning jets from said fine mesh element through said lower layer of said bed during operation of said backwash means whereby said hydraulic cleaning jets extend upwardly through said bed during backwashing.
Claim 23
Dependent Claim
32 words
The improvement as defined in claim 19 wherein said means for creating the hydraulic cleaning jets includes a plurality of nozzles facing toward said bed from immediately below said fine mesh element.
Claim 24
Dependent Claim
18 words
The improvement as defined in claim 20 wherein said fine mesh element is a generally flat metal screen.
Claim 25
Dependent Claim
18 words
The improvement as defined in claim 19 wherein said fine mesh element is a generally flat metal screen.
Claim 26
Dependent Claim
18 words
The improvement as defined in claim 14 wherein said fine mesh element is a generally flat metal screen.
Claim 27
Dependent Claim
47 words
The improvement as defined in claim 14 wherein said filtered effluent directing means includes a conduit connecting said underdrain cavity with a receptacle having an overflow plate and means for adjusting the vertical position of said overflow plate to control the minimum liquid level in said tank.
Claim 28
Dependent Claim
18 words
The improvement as defined in claim 9 wherein said fine mesh element is a generally flat metal screen.
Claim 29
Dependent Claim
106 words
The improvement as defined in claim 9 wherein said backwash means includes an elongated gullet extending in said underdrain cavity and generally across said tank, said gullet including a recessed channel having two spaced side walls, a central conduit with a first end, side walls located laterally inwardly of said gullet side walls and with apertures facing said gullet side walls and means for forcing filtrate into said conduit at said first end whereby said filtrate flows outwardly against said gullet side walls and then into said underdrain cavity and wherein said lateral side walls of said conduit converge in a direction from said first end.
Claim 30
Dependent Claim
24 words
The improvement as defined in claim 26 including at least one adjustable energy dissipating vane in said conduit and spaced from said first end.
Claim 31
Dependent Claim
19 words
The improvement as defined in claim 27 including means external of said filter for adjusting said energy dissipating vane.
Claim 32
Dependent Claim
108 words
The improvement as defined in claim 9 wherein said backwash means includes an elongated gullet extending in said underdrain cavity and generally across said tank, said gullet including a recessed channel having two spaced side walls, a central conduit with a first end, side walls located laterally inwardly of said gullet side walls and with apertures facing said gullet side walls and means for forcing filtrate into said conduit at said first end whereby said filtrate flows outwardly against said gullet side walls and then into said underdrain cavity and further including at least one adjustable energy dissipating vane in said conduit and spaced from said first end.
Claim 33
Dependent Claim
19 words
The improvement as defined in claim 29 including means external of said filter for adjusting said energy dissipating vane.
Claim 34
Dependent Claim
47 words
The improvement as defined in claim 9 wherein said filtered effluent directing means includes a conduit connecting said underdrain cavity with a receptacle having an overflow plate and means for adjusting the vertical position of said overflow plate to control the minimum liquid level in said tank.
Claim 35
Dependent Claim
177 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity, the improvement comprising: an hydraulic means for creating a plurality of horizontal liquid jets at a given location above said upper surface of said bed and evenly distributed across said bed and means for energizing said hydraulic means when liquid above said filter bed exceeds a given level higher than said given location.
Claim 36
Dependent Claim
177 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity, the improvement comprising: an hydraulic means for creating a plurality of horizontal liquid jets at a given location above said upper surface of said bed and evenly distributed across said bed and means for energizing said hydraulic means when liquid above said filter bed exceeds a given level higher than said given location.
Claim 37
Dependent Claim
45 words
The improvement as defined in claim 32 including means for sensing a preselected level of liquid above said upper surface and above said given location and means for energizing said hydraulic means when the level of said liquid is sensed by said level sensing means.
Claim 38
Dependent Claim
60 words
The improvement as defined in claim 32 including backwash means for forcing filtered liquid into said underdrain cavity, through said fine mesh element, through said filter bed from said lower surface to said upper surface at a flow rate sufficient to expand said filter bed to provide said bed with a second expanded upper level and then from said tank.
Claim 39
Dependent Claim
37 words
The improvement as defined in claim 34 including means for actuating said hydraulic means during operation of said backwash means and means for locating said hydraulic means to create said horizontal jets above said expanded upper level.
Claim 40
Dependent Claim
56 words
The improvement as defined in claim 35 including means below, but at, said fine mesh element for creating a plurality of evenly distributed hydraulic cleaning jets from said fine mesh element through said lower layer of said bed during operation of said backwash means whereby said hydraulic cleaning jets extend upwardly through said bed during backwashing.
Claim 41
Dependent Claim
32 words
The improvement as defined in claim 36 wherein said means for creating the hydraulic cleaning jets includes a plurality of nozzles facing toward said bed from immediately below said fine mesh element.
Claim 42
Dependent Claim
268 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface, a lower layer of particulate material immediately above said fine mesh element and substantially below said upper surface, and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity, backwash means for forcing filtered liquid into said underdrain cavity, through said fine mesh element, through said filter bed from said lower surface to said upper surface at a flow rate sufficient to expand said filter bed and then from said tank, the improvement comprising: means separate from said backwashing means and below said fine mesh element for creating a plurality of evenly distributed hydraulic cleaning jets separate from said backwashing means, initiated at said fine mesh elements, extending upwardly through said fine mesh element and passing through said lower layer of said bed during operation of said backwash means whereby said separate hydraulic cleaning jets and forced filtered liquid separately flush said lower layer from said fine mesh element while said filter is being backwashed.
Claim 43
Dependent Claim
268 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface, a lower layer of particulate material immediately above said fine mesh element and substantially below said upper surface, and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity, backwash means for forcing filtered liquid into said underdrain cavity, through said fine mesh element, through said filter bed from said lower surface to said upper surface at a flow rate sufficient to expand said filter bed and then from said tank, the improvement comprising: means separate from said backwashing means and below said fine mesh element for creating a plurality of evenly distributed hydraulic cleaning jets separate from said backwashing means, initiated at said fine mesh elements, extending upwardly through said fine mesh element and passing through said lower layer of said bed during operation of said backwash means whereby said separate hydraulic cleaning jets and forced filtered liquid separately flush said lower layer from said fine mesh element while said filter is being backwashed.
Claim 44
Dependent Claim
18 words
The improvement as defined in claim 38 wherein said fine mesh element is a generally flat metal screen.
Claim 45
Dependent Claim
242 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity through said bed during backwashing, the improvement comprising: a first set of upper nozzles in said bed and spaced only slightly above said fine mesh element and evenly distributed throughout said filter bed, a second set of lower nozzles near to, but below, said fine mesh element and also evenly distributed through said filter bed, said second set of nozzles being separate from said filtered effluent directing means, means for periodically forcing liquid through said upper nozzles whereby the upper surface of said bed is periodically regenerated at least during filtering and means for forcing liquid through said separate, lower nozzles during backwashing of said filter by liquid filtrate from said underdrain cavity whereby said bed is agitated.
Claim 46
Dependent Claim
242 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity through said bed during backwashing, the improvement comprising: a first set of upper nozzles in said bed and spaced only slightly above said fine mesh element and evenly distributed throughout said filter bed, a second set of lower nozzles near to, but below, said fine mesh element and also evenly distributed through said filter bed, said second set of nozzles being separate from said filtered effluent directing means, means for periodically forcing liquid through said upper nozzles whereby the upper surface of said bed is periodically regenerated at least during filtering and means for forcing liquid through said separate, lower nozzles during backwashing of said filter by liquid filtrate from said underdrain cavity whereby said bed is agitated.
Claim 47
Dependent Claim
27 words
The improvement as defined in claim 40 including means for forcing chemical cleaning substance through at least some of said nozzles during cleaning of said filter bed.
Claim 48
Dependent Claim
246 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface of said bed and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity through said bed for backwashing during times between filtering by said bed, the improvement comprising: a first network of upwardly facing nozzles evenly spaced throughout said bed, substantially below said upper surface of said bed and above said flat fine mesh element a selected distance to retain a lower layer of said bed generally undisturbed when jets are directed through the upper portion of said bed above said nozzles, means for forcing filtered effluent through said nozzles of said first network in a series of bed surface regenerating cycles during filtering by said bed between backwashing of said total bed by a means for forcing liquid from said underdrain upwardly through said total bed including said retained lower layer.
Claim 49
Dependent Claim
246 words
In a waste effluent filter including a tank having a lower portion; a generally flat fine mesh element supported adjacent said lower portion and having a multitude of apertures; an underdrain cavity adjacent said lower portion and under said fine mesh element and generally coextensive with said fine mesh element; a filter bed of particulate material having an upper surface, a parallel lower surface on said generally flat fine mesh element, a generally uniform depth between said fine mesh element and said upper surface of said bed and an effective particle size at least greater than the size of said apertures of said fine mesh element; means for directing effluent into said filter above said upper surface; and, means for directing filtered effluent from said underdrain cavity through said bed for backwashing during times between filtering by said bed, the improvement comprising: a first network of upwardly facing nozzles evenly spaced throughout said bed, substantially below said upper surface of said bed and above said flat fine mesh element a selected distance to retain a lower layer of said bed generally undisturbed when jets are directed through the upper portion of said bed above said nozzles, means for forcing filtered effluent through said nozzles of said first network in a series of bed surface regenerating cycles during filtering by said bed between backwashing of said total bed by a means for forcing liquid from said underdrain upwardly through said total bed including said retained lower layer.
Claim 50
Dependent Claim
45 words
The improvement as defined in claim 42 including a second network of upwardly facing nozzles evenly spaced throughout said bed below said fine mesh element and means for forcing filtered effluent through said nozzles of said second network while said filter bed is being backwashed.
Claim 51
Dependent Claim
21 words
The improvement as defined in claim 43 wherein said nozzles of said second network are generally against said fine mesh element.
Claim 52
Dependent Claim
18 words
The improvement as defined in claim 44 wherein said fine mesh element is a generally flat metal screen.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-12-08 | 1990-06-09 | 1990-12-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-12-08 | 1994-06-09 | 1994-12-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-12-08 | 1998-06-09 | 1998-12-09 | $7700.00 | Window Closed / Lapsed |