eli5: If water is non-compressible, then why not use it in hydraulic machines instead of hydraulic oil?

Question

eli5: If water is non-compressible, then why not use it in hydraulic machines instead of hydraulic oil?

In: 1817

Answer 1

Oil is a lubricant itself, water machinery tends to have short lived seals in moving parts because water makes them seize by washing away the lubricants.

Water freezes, that’s something you really don’t want in a system.

Water is corrosive to certain metals.

Water boil sooner than oil, making problems to hot machinery.

Water boiling point is very low if you reduce the pressure below atmospheric one, this leads to vapors in some parts of the system, and a lot of cavitation in the pumps, cavitation is predominant in low life expectancy for valves and pumps, it’s the biggest factor in the deterioration of those. This doesn’t mean you can’t avoid cavitation, it’s that preventing cavitation requires more complex machinery.