The present piston pump conveys concrete mixes through, for example, two pump cylinders located in a frame structure so that the cylinder axes extend substantially in parallel to each other. The pump cylinders cooperate with scavenging chambers also installed in said frame structure. To facilitate the assembly and disassembly of said pump cylinders in said frame structure without disassembling the entire frame structure, releasable, form locking connecting elements are operatively arranged between the frame structure and the scavenging chambers whereby the latter may be axially shifted in the frame structure for removing the pump cylinders from their sockets in the frame structure, for example, for maintenance work. Upon insertion of the cylinders into the frame structure, the connecting elements are tightened whereby the pump cylinders are held in position in the frame structure by the connecting means through said scavenging chambers.