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 and cover in die-cast aluminium alloy. Side cover may be blind or incorporate oil sight glass. Rear cover with oil drain outlet and sight glass. Pistons driven by crank-connecting rod mechanism. Pump shaft in pressed high-strength steel. Oversized friction bearings. Connecting rods in die-cast special low-friction zinc-aluminium alloy. One-piece ceramic pistons. Pump head in pressed brass. Double gasket sealing system. Intake and delivery valves have plugs for easier maintenance.