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The short answer: Cost effectiveness.
The long answer: Employing water as a hydraulic fluid is entirely possible for many applications, but produces several additional challenges which will dramatically and likely prohibitively raise the price of the apparatus. For most applications, the higher costs will represent an unmarketable product.
The issues include:
Viscosity: Water has a much lower viscosity and higher specific gravity than hydraulic oil. This results in at least 3 other issues. First, the piston and cylinder materials (usually steel) will erode much quicker due to the resulting higher velocity and more turbulent flow. Second, the use of special valves will be required to prevent the mechanical shock caused by abrupt fluid flow stoppage inherent to water. Third, the lower viscosity also means it will be more difficult to prevent leaks, requiring more stringently machined parts with much finer tolerances.
Bacteria: A closed water system can provide a breeding ground for all kinds of microorganisms. This can result in clogged lines, filters and a potentially unsafe/unhealthy condition in the event of a leak.
Corrosion: Oxygen in the water as well as sulfurous by-products from bacteria can potentially corrode component materials.
Temperature Range: Water freezes at 32 degrees Fahrenheit. If freezing occurs, and due to the non-compressible nature of ice, it will almost certainly damage or destroy hydraulic parts. Anti-freeze agents will need to be utilized at the cost of the inherent environmental and toxicity concerns of such substances.
Lubricity: Water's comparatively low lubricity will lead to increased contact friction and resulting wear of components.
All of these issues can be addressed and overcome, with the disadvantage of dramatically higher cost vs. hydraulic oil.
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Can you put water in a hydraulic jack?
you can but you'll be buying a new one very shortly afterwards. Use hydraulic fluid. Brake fluid works well also
What energy isolating devices is most likely associated with hydraulic systems?
outer screw-in yoke
Which one is dangerous hydraulic or pneumatic?
Pneumatic systems are inherently more dangerous than hydraulic systems at the same pressures. Most states have laws governing the construction of compressed air systems for just this reason. The ASME Code section 8 specifies rules for construction of air tanks (unfired pressure vessels). There are less regulations on constructing hydraulic systems. An overpressure on an air tank could result in the explosive destruction of the tank, whereas a cracked hydraulic tank would result in just a leak.
Why are aircraft hydraulic power supplies colour coded?
I think they decided that it was just more user friendly and more fool proof than numbers. (747's hydraulic systems are numbered) The color coding of the hydraulic lines is a European practise. The Boeing designs and most US designed a/c have their hdraulic systems numbered. The color code is really just a way to Identify the separate systems in the documentation and the cockpit procedure as well as physically on the hydraulic tubing.
What happens if oils are used insteat of water in hydraulic jacks?
Most jacks use oil and not water so nothing adverse would happen.
