PURPOSE: To make a wear ring replaceable simply and easily from a flushing opening part beneath a valve casing by installing this wear ring slidable contact with the pump cylinder side, in a valve body, in a concrete pump which is made so as to rock this valve body and to interconnect a pair of pump cylinders to a discharge pipeline in an alternate manner.

CONSTITUTION: A valve body 11 is rockably installed in a valve casing having a flushing opening part 15 beneath, and a pair of pump cylinders 2 and 2 are made so as to be mutually interconnected to a discharge pipeline by dint of a rocking motion of the valve body 11. In addition, a wear ring 24 in slidable contact with the side of these pump cylinders 2 and 2 is installed in the valve body 11 while this wear ring 24 is clamped with a half-form holddown member 28 or part of the valve body 11 at a lower part of the wear ring 24, and this holddown member 28 is removed beneath from the opening part 15 whereby the wear ring 24 is made so as to be replaceable in design.