eli5: If water is non-compressible, then why not use it in hydraulic machines instead of hydraulic oil?
In: 1817
Also, water can be compressed, as can any liquid. It just takes an insane amount of force compress a liquid even a tiny bit.
Water has a couple of problems that are particularly important when thinking about machinery
– It freezes below 0°, and boils at 100°. That’s a very specific temperature, and its performance will vary within that range. If it gets too cold, your machine is almost certainly broken because of ice expansion. If it gets too hot, it can cease to be a liquid; your hydrolyic machine just became pneumatic.
– Water is corrosive. Extremely so. It’s known as the universal solvent for a reason; This stuff tears down mountains, and reduces the ocean floor to loose sand.
The main reason water is unsuitable for modern hydraluic applications is because modern systems run at high pressures and high temperatures. Under the conditions most modern hydraulics run, water would cavitate (convert to a gas). Once there is gas in a hydraulic system it can not function.
A lot of London was powered by high pressure water mains. Tower bridge was powered that way. As a child I was taken to see the steam engines presurising the system. Now the same hydraulic actuators in the bridge are fed with pressurised oil.
Water IS compressible. That’s a common misconception. It’s not VERY compressible, but there’s some wiggle room in there.
Won’t be weighing in on the rest because idfk lol
Valves in water systems use water as a working fluid in hydraulic cylinders all the time. It helps when you don’t care about minor leakage and have a relatively infinite supply
While there are a lot of good comments here talking about why water isn’t used, I want to point out that using water as a working fluid is increasing in popularity, though it still suffers from major drawbacks.
The biggest benefits of using water as the working fluid in a hydraulic system are cost of fluid and cost of disposal. Water is obviously pretty cheap most places and earth and fairly easy to purify, but the real cost savings come when your system starts to leak fluid everywhere or just when it comes time to replace the fluid. Water is safe to dump pretty much anywhere. If your hydraulic oil leaks everywhere you have a major environmental issue if you don’t clean it up properly and promptly, which can be pretty expensive. If your hydraulic water system leaks you just have some presumably clean water getting into the environment and the plants don’t care. Cleanup, if it’s even needed, is super cheap because you just need some normal pumps and can just dump the water in the nearest river.
The downsides to water systems mostly come down to temperature range and corrosion/lubrication issues. The temperature thing can be mitigated somewhat by the use of antifreeze additives, but those reduce the cost savings and environmental benefits of using a water system. The corrosion and lubrication issues can be fixed by increasing maintenance, which also increases costs, but many places where temperature isn’t an issue, such as mines, the increased maintenance costs are less than the costs savings on fluid and disposal or the potential costs of a spill of hydraulic oil.
Water is compressible, otherwise the speed of sound in water would be infinite. It’s hard to compress water and the speed of sound is very high, but it’s not infinite.
how are we going to drink the water if it’s inside of a hydraulic machine being utilised in the place of hydraulic oil!!
Many of the answers here are good. However in the 1980’s there was a push to use water based fluids in the Industrial Hydraulics Industry. Think inside a heated factory. The fluids were called 95/5 as they were 95% water and 5% additives designed to combat the negative affects noted by others. While there was some success the lower lubricity caused problems most manufacturers had trouble overcoming. The faults were shorter life of the components. When I left the industry in the mid 1990’s most companies had abandon the development of water based hydraulics.
This development never made headway in the mobile industry. Think excavators and outdoor machinery for the reasons many have noted here.
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