## Facts

- Amstar owned U.S. Patent No. 3,523,889, directed to processes and apparatus for removing suspended solids from a liquid–solid slurry, including clarification in sugar manufacturing.
- Amstar sued Envirotech Corporation and Envirotech’s customer/user, Energy Fuels Nuclear, Inc., alleging infringement by Envirotech’s “Enviro-Clear” clarifier systems.
- The patented clarifier, as construed by the courts, relied on controlled flow patterns and gravity separation to maintain a sludge blanket, without an internal mechanically driven stirring element.
- Envirotech’s accused clarifier included a mechanically driven mixer/agitator in the sludge blanket region, actively stirring solids to maintain slurry uniformity and improve settling.
- After trial, the district court upheld validity but found no infringement, concluding that the mechanical mixer was not within the claims and represented a meaningful operational difference.

## Issues

1. Whether Envirotech’s clarifier systems literally infringed the asserted claims when the accused systems used a mechanically driven mixer not present in the claimed invention as construed.
2. Whether Envirotech’s clarifier systems infringed under the doctrine of equivalents despite the addition of a mechanical mixer that altered the clarifier’s operation.
3. Whether the district court’s technical fact-findings concerning the function and significance of the mixer required affirmance on appeal.

## Decision

- The Federal Circuit affirmed the judgment of noninfringement.
- The court held there was no literal infringement because the properly construed claims did not cover a clarifier incorporating an internal mechanical mixer in the sludge blanket region.
- The court held there was no infringement under the doctrine of equivalents because the mixer was a substantial structural and functional change that altered the mode of operation.
- The court relied on, and did not disturb, the district court’s technical findings comparing how the patented and accused systems maintained and circulated solids.

## Legal Principles

- Literal infringement requires the accused device to fall within the claims as properly construed in view of the specification and prosecution history.
- Claim scope may be limited by the patent’s disclosure when the asserted construction would extend the claims beyond the described principle of operation.
- The doctrine of equivalents does not extend to an accused device that adds a structurally significant component producing a materially different way of achieving the result.
- Appellate review gives deference to trial-court technical fact-findings that are based on detailed comparisons and expert testimony.

## Conclusion

The Federal Circuit affirmed noninfringement because the accused clarifier’s mechanically driven mixer was a material structural feature that changed how the system operated, placing it outside both the literal scope of the claims and the permissible reach of the doctrine of equivalents.


Amstar Corp. v. Envirotech Corp., 730 F.2d 1476 (Fed. Cir. 1984)