| CPC F16K 1/2261 (2013.01) | 18 Claims |

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1. A valve disc for a butterfly valve, the valve disk comprising: a disc body, wherein the disc body comprises: first and second faces; an outer periphery; at least one engagement means configured to receive a shaft for coupling the valve disc to a valve body of the butterfly; a main groove suitable for receiving a seal element, wherein the main groove extends along the outer periphery to form a continuous groove; and an introduction groove, wherein the introduction groove has a centreline (CL2) and extends from a groove mouth opening in one of the faces of the disc body to an intersection with the main groove; wherein the main groove is shaped so that the seal element can only be inserted into or removed from the main groove via the introduction groove; wherein a cross-section of the main groove in a plane perpendicular to the direction in which the main groove extends (CL1) is a shape such that the seal element cannot be pulled out of the main groove other than in a direction along the centreline (CL2) of the introduction groove.
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