Case 28: Graver Tank & Mfg. Co. v. Linde Air Products Co. (1950)

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Linde Air accused Graver of infringing their patent for electric welding processes and the flux used in them. The District Court held some claims invalid and others valid and infringed; the CAFC ruled the invalid claims were valid, but this decision was overruled by the Supreme Court and the original decision of the District Court was reinstated. The Supreme Court's sole decision was whether the four flux claims were valid and infringed.

If the accused matter is clearly contained within the claims, then it infringes. But if patents only cover their literal definitions, then copyists could make minor, insignificant changes and avoid infringement. This form of piracy is most common; outright infringement is dull and useless. To combat this, the courts instituted the doctrine of equivalents. This doctrine means that a feature of an accused device infringes a claim "if it performs substantially the same function in substantially the same way to obtain the same result."