MadSci Network: Physics |
Either your professor was wrong or you misunderstood him/her. Water is a good hydraulic fluid from a physics standpoint, but not necessarily good from an engineering (practical) standpoint.
Water is almost incompressible, though it can actually be compressed. At a tremendous pressure of 1000 kg per square centimeter (which isn't strictly a pressure, but is listed that way in Smithsonian Physical Tables) water compresses by only 2.5% at 50 degrees C.
Water actually can be used as a hydraulic fluid in situations where it doesn't matter that it evaporates easily, if the components of the hydraulic system don't corrode easily, and if the temperatures in the system are low enough that the water won't boil. Due to these material considerations (volatility, corrosion, and temperature) most hydraulic systems use oils of various kinds.
John Link, MadSci Physicist
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