A high pressure sea water pump has been developed for variable ballast system of 6,000m deep submersible and for high pressure sea water power source of under water working machine system. To develop the very high delivery pressure, small, lightweight, high operating speed and high efficiency pump, the axial plunger type is adopted in this sea water pump. To minize the wear and corrosion caused by the siltcontaminated sea water, and to enable the pumping by a close clearance sealing with high speed, ceramic materials are used for cylinders and plungers. Various tests, such as friction tests of cylinder and plunger, performance tests and endurance tests of sea water pump etc. are carried out, and good performances are obtained. From test results, outlet flow is 6.4 l/min, Volumetric efficiency is 81% and overall pump efficiency is 87.4% (for 2,000rpm operating speed, 630kgf/cm^2 delivery pressure).
