A butterfly valve, comprising a housing containing a through-opening; BUTTERFLY VALVESa butterfly disk which is opened or closed by rotation of the butterfly disk on a shaft connected to the housing so that contact between an outer periphery contact portion of the butterfly disk with a sealing surface of a seat ring mounted at the through-opening of the housing results in closure of the through-opening, Butterfly Valveswherein at least a first pair of notches are respectively formed on the contact portion adjacent each other in respect of contact with opposing faces of the disk and cooperating with each other so that the remaining sealing area between the notches is smaller than other sealing areas adjacent thereto on the contact portion, said first pair formed adjacent one end of the shaft and a second pair of notches, Butterfly Valvessubstantially identical to the first pair, formed at the other end of the shaft such that both said sealing areas between the respective notches are the smallest sealing areas on the contact portions to minimize the sealing area around the shaft and avoid disk abrasion, said notches each extending along the contact portion through about 90°.

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