A clack valve assembly comprising: a valve seat comprising an opening; a bearing comprising a recess with a base, a mouth, and a pair of side walls between the base and the mouth; a lid comprising a lid plate and a shaft, the shaft being received in the recess of the bearing; and a shaft retaining member which closes the mouth of the recess in the bearing, thus retaining the shaft within the recess. The shaft and the lid plate are integrally formed elements of a single part. The shaft can rotate within the recess to enable the lid to rotate from a closed position in which the lid engages the valve seat and covers the opening, to an open position in which the lid lifts away from the valve seat enabling fluid to flow through the opening in the valve seat.