904 F.2d 1571 (Fed. Cir. 1990), 89-1596, Envirotech Corp. v. Westech Engineering Inc.

Docket Nº:89-1596.
Citation:904 F.2d 1571
Party Name:15 U.S.P.Q.2d 1230 ENVIROTECH CORPORATION d/b/a Eimco Process Equipment Company, Plaintiff-Appellant, v. WESTECH ENGINEERING INCORPORATED, James V. Larsen and Lowell L. Palm, Defendants-Appellees.
Case Date:June 05, 1990
Court:United States Courts of Appeals, Court of Appeals for the Federal Circuit

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904 F.2d 1571 (Fed. Cir. 1990)

15 U.S.P.Q.2d 1230

ENVIROTECH CORPORATION d/b/a Eimco Process Equipment

Company, Plaintiff-Appellant,



L. Palm, Defendants-Appellees.

No. 89-1596.

United States Court of Appeals, Federal Circuit

June 5, 1990

Rehearing Denied July 2, 1990.

Suggestion for Rehearing In Banc Declined Aug. 28, 1990.

Gordon L. Roberts, Parsons, Behle & Latimer, Salt Lake City, Utah, argued for plaintiff-appellant. With him on the brief were Raymond J. Etcheverry, David G.

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Mangum, C. Kevin Speirs. Also on the brief were William S. Britt and Thomas J. Rossa, Trask, Britt & Rossa, Salt Lake City, Utah, of counsel.

Earl D. Tanner, Sr., Tanner, Bowen & Tanner, Salt Lake City, Utah, argued for defendants-appellees. With him on the brief was Richard F. Bojanowski, Salt Lake City, Utah.

Before ARCHER, MAYER and PLAGER, Circuit Judges.


MAYER, Circuit Judge.

Envirotech Corporation appeals the judgment of the United States District Court for the District of Utah, 713 F.Supp. 372, 11 USPQ2d 1804 (1989), holding U.S. Patent No. 4,391,705 (Cook) invalid under 35 U.S.C. Sec. 102(b) (1982). We reverse and remand.


The patented invention is a ballasted digester cover for use in wastewater treatment plants. Dubbed a "hydroballaster" by its inventors, Envirotech employees Lynn Cook and David Brown, the invention is a floating (as opposed to fixed) cover-type digester consisting of a circular steel top with cylindrical sidewalls that slide up and down telescopically inside a large cylindrical steel tank. The tank contains sewage sludge that, when digested by microorganisms, supplies a large volume of methane and other gases on which the cover "floats." Appropriately ballasting the lower rim of the cover enables it to maintain these gases at a predetermined and constant design pressure, making the gas available to fuel other components of the treatment facility.

Archimedes' Principle--that an object wholly or partially submerged in fluid is buoyed up by a force equal to the weight of the fluid displaced--dictates the ballast design of all floating cover digesters. The Cook invention implements this principle by attaching tub-shaped concrete blocks to the bottom of the cylindrical sidewalls of the floating cover. When submerged, these "hydroballast" blocks displace the same amount of sludge and therefore weigh the same as traditional, solid concrete blocks composed of an equal volume of concrete. Thus, because pressure is directly proportional to weight, the Cook invention achieves the same gas operating pressure as a traditionally ballasted digester when their respective ballasts are submerged. However, when a hydroballast block is emerged it outweighs an equal volume traditional block by the weight of the sludge filling the block cavity. Accordingly, the Cook invention can achieve a specified gas operating pressure using significantly less concrete than--or, conversely, attain a higher gas operating pressure using the same amount of concrete as--a cover ballasted only with traditional blocks when their respective ballasts are emerged.

It is principally the Cook invention's ability to attain a higher pressure differential between its submerged and emerged positions that makes it superior to a traditionally ballasted digester. Prior to the Cook invention, engineers using traditional ballast blocks resorted to various techniques to increase the achievable pressure differential. One technique was to construct the blocks of low-density concrete: the additional concrete volume necessary to equal the weight of an emerged, traditional density block displaced proportionately more sludge when submerged, thereby creating a larger weight differential between the emerged and submerged blocks and, thus, a larger pressure differential. A second technique, relevant here, combined traditional ballast blocks with an air-filled steel buoyancy ring. This technique allowed a higher pressure differential because of the increased buoyant force the ring provided when submerged.

Envirotech Corporation (Envirotech) is engaged in the design and sale of ballasted digester covers for use in municipal wastewater treatment plants. In response to a December 1979 invitation to bid on an addition to the Nine Springs Wastewater Treatment Plant in Madison, Wisconsin (Madison project), Envirotech submitted proposals for a digester cover to all general contractors

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bidding the mechanical portion of the project. In these February 21, 1980 proposals, Envirotech offered to provide for $205,000 a digester cover constructed in accordance with the plans and design specifications of the consulting engineer on the Madison project, CH2M-Hill (Hill). To achieve the desired gas operating pressure, the Hill design specified the use of traditional solid concrete ballast blocks together with an air-filled buoyancy ring constructed of steel.

For reasons not relevant here, Hill decided not to award the mechanical portion of the Madison project...

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