3-piston alternating volumetric pumps for use on cleaning units and industrial systems. Can be coupled to various types of motors, directly or with flexible joint. Pump body in die-cast aluminium alloy with oil drain outlet. Rear cover with oil sight glass. Pistons driven by crank-connecting rod mechanism. Pump shaft in pressed high-strength steel. Oversized friction bearings. Connecting rods in bronze. One-piece ceramic pistons. Pump head in pressed brass. Double gasket sealing system. Intake and delivery valves have plugs for easier maintenance.