Can Water Replace Hydraulic Oil in Hydraulic Machines?

In recent years, there has been an increased tendency of industries to move away from depending on oil and its by-products and using on alternative fuel instead of oil. Research has shown that in hydraulic equipment where there is the continuous use of hydraulic oil for its operation, a potential substitute of the oil can be water. But the question is how effective water will be as a substitute for hydraulic oil. All hydraulic machines use oil to power the pumps, valves, and cylinders that are the heart of this type of industrial machine. The hydraulic oil when is under pressure powers the cylinders, which exerts force and perform the task for which they were produced. This is a simple technology but can water exerts the same force and power? In the past, hydraulic equipment powered by water has been in use, especially when the application called for a fire-resistant or fire-proof hydraulic machine. Water based hydraulic machines were required in foundries and other industries where there is always high level of flame or fire use in the manufacturing processes. But, it is seen that in all these water based hydraulic machines, there was also the use of some kind of additive with water to create the lubrication factor, usually 95% water, 5% additive.

It was almost 10 years back, the first ever line of hydraulic components to operate with pure water, without additives was introduced. This was done by a leading hydraulic equipment company by the name of Danfoss. The new hydraulic machine was fireproof and also 100% green. Following that example, many industries produced an entire line of components to provide a complete water hydraulic system, that perform at levels much higher than oil is presently capable of. Besides the water hydraulic systems, in any equipments, where water is used as the pressure medium, these new components can be used. In some equipment, it is possible to use the water to power the hydraulics, as well as spraying that same water for cleaning or fire suppression.

Advantages of Water Hydraulics

Water is not flammable like oil.

Water is more friendly to the environment compared to oil. It is an obvious applications in fire safety.

Water also has a lower viscosity than oil. This implies that water has a lower pressure drop when applied at the same flow rate as oil.

With all factors equal, water can transmit power more efficiently than oil, and that too within a smaller space. The main benefit is a water-based system holds a potential for a higher power density than any oil-based system.

Water can also transfer heat more efficiently than oil.

When water is used in hydraulic system, a smaller heat exchanger is required compared to the one used in oil, thereby saving space and money for smaller technology.

Disadvantages of Water Hydraulics

Due to low viscosity of water, it poses a greater challenge to sealing components. Leaks from a pipe, rod or shaft may not be a great problem like oil would, but it is a matter of concern for lower volumetric efficiency. To solve this problem, nonmetallic seals will have to be used and extremely hard materials are needed to make the moving surfaces, with very smooth finishes, as there is lower lubrication factor.

The lines drawing the water through the pump will have to be pressurized to compensate for water's higher vapor pressure. Water hydraulic systems will not be able to operate within certain temperatures, simply because water freezes faster than oil. The lines of components that will have to be fabricated for some of the simplest machinery may not, in the long run, make water a viable substitute for oil.