3-piston alternating volumetric pumps for use on cleaning units and industrial systems. Hollow shaft version pump with included flange for gasoline engine ø 1″SAE J609a. Pump body and cover in die-cast aluminium alloy. Side cover incorporate oil sight glass. Oil level on pump body. Rear cover with oil drain outlet. Pistons driven by crank-connecting rod mechanism. Pump shaft in pressed high-strength steel. Oversize friction bearings. Connecting rods in bronze. One-piece ceramic pistons. Pump head in nickel-plated brass. Double gasket sealing system. Intake and delivery valves have plugs for easier maintenance.