Kohler Mira Limited v Norcros Group (Holdings) Limited

Patent claims are construed purposively and in the context of the invention described in the specification. A functional requirement such as flow being substantially unchanged may have an objective meaning when read by reference to the technical problem addressed by the patent.

Where a claimed component operates as part of a system, its configuration may be assessed in the context of that system. A patent is not insufficient merely because its boundary is imprecise, provided the skilled person can determine it using ordinary construction techniques and can perform the invention.

A prior disclosure does not anticipate unless it clearly and unambiguously discloses, and enables, every claimed feature. A simple solution may still involve an inventive step where it results from recognising and solving a problem that had remained unresolved in the art.

Kohler Mira Limited claimed infringement of GB 2,466,504, a patent concerning instantaneous water heaters and, particularly, dual-outlet electric showers. Norcros Group (Holdings) Limited denied infringement and counterclaimed for revocation on grounds of lack of novelty, obviousness and insufficiency.

The principal prior art was UK Patent Application No 2,274,985A (Deeley), read with its cross-reference to UK Patent No 2,219,497B (McMaster-Christie). The court also had to construe the expressions substantially unchanged and the diverter valve is configured so that in claim 1.

The issues were whether claims 1, 4 and 17 were valid and whether the defendant’s DuElec Range fell within claims 1 and 4.

1. Construction. The expression substantially unchanged was construed by reference to the patent’s technical purpose. It meant that, during changeover between outlets, any increase in temperature should not give rise to a real risk of scalding. The claim was directed to ablutionary installations involving potential user exposure to the outlet water, particularly electric showers, rather than closed installations such as dishwashers.
2. The requirement that the diverter valve be configured so that the flow rate was substantially unchanged concerned the operation of the valve in the context of the complete installation. It did not require the result to be produced solely by the diverter valve, considered in isolation.
3. Novelty. Under Patents Act 1977, section 2(1), anticipation required clear and unambiguous disclosure of every feature, together with enablement. Deeley disclosed a dual-outlet mixer shower. Its cross-reference to McMaster-Christie did not clearly or enablingly disclose an instantaneous water heater with a downstream diverter valve directing heated water between outlets. Deeley also taught reducing flow to a trickle and terminating it, contrary to the claimed substantially unchanged flow rate. Claims 1, 4 and 17 were therefore novel.
4. Inventive step. Applying section 3 of the Patents Act 1977, the inventive concept was the recognition that a diverter valve in a dual-outlet electric shower could create a scalding risk, together with the solution of configuring it to maintain substantially unchanged flow during changeover. The skilled person would regard mixer and electric showers as practically distinct fields requiring a different engineering mindset. Moving from Deeley to the claimed invention required more than routine work and was not obvious. The same conclusion applied over the common general knowledge alone. Claims 4 and 17 were also inventive.
5. Sufficiency. Section 72(1)(c) was not infringed. The claim boundary was capable of determination by purposive construction, and the risk of scalding was known and measurable. The evidence showed that the skilled person could make a suitable diverter valve without undue difficulty.
6. Infringement. The DuElec Range contained all the elements of claim 1. Although the diverter valve’s aperture varied during changeover, the valve operated with the other components of the system to maintain flow and avoid a scalding risk. The products therefore infringed claim 1 and, consequentially, claim 4. It was unnecessary to decide infringement by equivalence or the Formstein defence.