Hydraulic fluids are considered as the lifeblood for any hydraulic system. Then what will happen when you choose water as a hydraulic fluid? In my opinion, water is considered as the worst fluid for any hydraulic application. Water has all properties of fluid but we can’t able to select them due to the risk of corrosion and less lubricating value. Also, the continuous flow of water will increase the temperature and hence it will damage the system components.
We discussed the reasons for not selecting water as a hydraulic fluid. But, what will happen if water is already present in your hydraulic oil? This article deals with the effects of water in hydraulic oil, hydraulic oil-water separator, methods to identify the presence of water in oil, etc.
The ability of a fluid to release water content is called demulsibility property. Not all fluids will have this property. But before choosing a fluid for your application, check this property and the effect on your system performance.
Water can present in the hydraulic oil in 3 forms: emulsified, dissolved and free. The presence of water in hydraulic oil will destroy both the physical and chemical properties. Increased viscosity and decreased load carrying capacity are the effect on physical properties. Aeration, reduced dielectric strength, and hydrolysis are the effects on chemical properties. The destruction of both these chemical and physical properties will create corrosion, wear, filter plugins, and cavitation to the hydraulic system.

There are different methods for hydraulic oil-water separation. Some are listed below

Gravity Separation

Gravity separation is an environmentally friendly, traditional approach that relies on the specific gravity. This is a cheaper approach that doesn’t require much temperature or chemicals. This is preferred when the water present in hydraulic fluid is free. In most of the cases, water will have more specific gravity than oil. So, they will settle down at the bottom of the reservoir when the fluid was kept still for a specific time period.

Centrifugal Separation

This is another method for separating free water from the oil. Centrifugal separation is more effective than gravity separation. This technique will magnify the difference between the specific gravity of fluid and water by spinning the fluid. To improve the centrifugation process a small amount of coagulant salt is added.

Also, Read: Hydraulic Fluid Properties

Coalescing Separation

Coalescing separation is an ideal solution for removing water from low viscosity oils. Coalescing means joining together. This separator will combine small water droplets to form larger ones which can be removed easily. This method is widely used in petroleum refining, petrochemicals and fine chemicals, parts cleaning facility, etc.

Absorbent Polymer Separation

Small amount of both free and emulsified water can be eliminated using this method. The water containing oil is passed through a polymeric filtration system. The water content gets trapped in the filter and this will cause the polymer to swell. This system is not adapted for applications that contain high water content.

Also, Read: Functions of Hydraulic Fluid

Vacuum Distillation

Free, emulsified, and dissolved water can be removed using this method. This technique includes heating, vaporization, condensation and cooling of vapours. It will remove not only water but also other contaminants like refrigerants, solvents and fuels.

Headspace dehumidification

This is another method used for removing free, emulsified and dissolved water. The operation involves removing air from the headspace of a sump. This is a filterless approach that uses the concept of equilibrium.