HD hydraulic oils are applied in modern hydraulic systems operating under moderate load and at relatively constant temperatures. Lower viscosity grade HD oils are used as hydraulic media for power transfer in high-precision low-power machines (spindles, grinding spindles, precision machine tools). Medium viscosity HD oil grades are used in medium-power-pressure-and-load hydraulic systems (presses, cranes, machine tools). Besides that, they are suitable for lubrication of medium-pressure toothed gear pumps and rotary piston pumps. Higher viscosity grade HD oils are used in high-temperature-and-load operating conditions.