What Are the Effects of Water in Hydraulic Oil?

There are a number of potentially detrimental effects commonly associated with any amount of water in hydraulic oil, including surface corrosion and the accelerated fatigue of metal components. Since water present in hydraulic oil can exist in three distinct states, the specific effects can depend on factors such as the water concentration, the type of oil, and the working temperature. Water that is fully dissolved in hydraulic oil is not typically associated with surface corrosion, but high levels of dissolved water can result in accelerated metal fatigue. The existence of water in hydraulic oil may also change the physical characteristics of the oil, resulting in reduced viscosity, or may even cause components to become jammed if ice crystals form under especially cold working conditions.

Hydraulic oils are a class of substances that are used to transfer power in various types of hydraulic machinery. In addition to functioning as a power transfer medium, hydraulic oil can also perform a number of other tasks. These oils are often used to lubricate, transfer heat, and act as a sealing medium. Some hydraulic oils are also designed specifically to be fire or radiation resistant. The ability of hydraulic oil to carry out these tasks is typically reduced by the presence of any water, though the specific effects of water in hydraulic oil depend on a number of factors.

When water contaminates hydraulic oil, there are three distinct states that it can exist in. Relatively small levels of water can be completely dissolved in large amounts of hydraulic oil, in which case the effects are typically minimal. Surface corrosion typically does not occur due to small amounts of dissolved water, though metal components within the system may suffer from accelerated fatigue. Studies have shown that a reduction of dissolved water levels from 400 parts per million (PPM) to 25 PPM can allow some components to last about five times longer.

Each type of hydraulic oil can contain a limited amount of water in a dissolved state. After that saturation point is reached, the results are either free water or an emulsion. Large amounts of free water in hydraulic oil typically result in a lot of surface corrosion, and very high levels often cause component failures. When the water in hydraulic oil is mixed into an emulsion, the result is typically a distinct change in the physical characteristics of the oil. That can result in hydraulic oil that has a different viscosity or compressibility, which can adversely affect the ability of the oil to transfer power.