Compressibility of Hydraulic Fluids

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Compressibility of Hydraulic Fluids

Compressibility of Hydraulic Fluid. Compressibility is a measure of the amount of volume reduction due to pressure. Compressibility is sometimes expressed by the bulk modulus, which is the reciprocal of compressibility. Petroleum fluids are relatively incompressible, but volume reductions can be approximately 0.5 percent for pressures ranging from 6900 kPa (1000 lb/sq in) up to 27,600 kPa (4000 lb/sq in). Compressibility increases with pressure and temperature and has significant effects on high-pressure fluid systems.

Problems directly caused by compressibility include the following: servos fail to maintain static rigidity and experience adverse effects in system amplification or gain; loss in efficiency, which is counted as power loss because the volume reduction due to compressibility cannot be recovered; and cavitation, which may cause metal fracture, corrosive fatigue, and stress corrosion.