Kidney loop filtration of lube oil saves you money on component replacement

01.06.21 10:00 AM Comment(s) By John Fernandes

Water in lube oil accumulates during usage

Water is widely considered as the second most destructive contamination to a lube system, after particulate contamination.

Where does water come from?

Water in lubrication systems can originate from the environment, such as rain or moisture in the air. Leakage, damaged gasket on reservoir covers, underperforming air breathers, or a damaged wiper on a hydraulic cylinder are also possible sources. Condensation of air in oil reservoirs due to temperature difference between day and night will turn any moisture in the air into water droplets, mixing with the oil. A damaged water-based cooling system in a steam application is another potential water source.

How does water exist in oil?

Water in oil can exist in three stages: dissolved, emulsified and free. Below saturation level, the molecules of water are dispersed alongside oil molecules, resulting in water in the oil that is not visible. This is known as dissolved water, the least dangerous water state to a lube system. When the amount of dissolved water exceeds the saturation point, the oil is no longer able to absorb more water molecules, resulting in emulsified water. This is characterised by a hazy or cloudy appearance of the oil. 

Further increments of water content in oil will result in separate levels between oil and water forming. This state is known as free water. Due to its higher density, the water forms the lower layer, settling at the bottom of the sump, with the oil floating on top. However, emulsified water will also be present in an intermediate phase, continuing to circulate in the lube system.

The saturation level of the oil is important, as it determines the amount of water that can be held before an emulsion will develop. Saturation level depends on base oil type, additive package, temperature and pressure. A highly refined mineral oil with minimum additive level has a saturation level of about 100 parts per million (ppm) at 70°F, whereas ester-based hydraulic fluids can have saturation levels of more than 3000 ppm at 70°F.

What type of damage can water do?

The effect of water in oil is two fold, destroying both the beneficial physical and chemical properties and characteristics of the oil. This can lead to machine component damage. For optimal protection of machine components the water content should not exceed 30% of the saturation point. Emulsions of water/oil occur mainly due to shear forces in machinery e.g. in pumps, gears and valves.

The problems caused by emulsified water are similar to those of free water i.e. corrosion, cavitation, micro-pitting and oil degradation. Degraded oil only separates water poorly, because the oxidation products (acid, aldehydes, ketones) are polar and encapsulate water droplets, hindering merging of drops and separation by gravitation.

During equipment operations lubricants are contaminated by wear debris, water and oil residues such as sludge or varnish depending on severity and operating conditions. Kidney loop filtration if employed, can remove these contamination efficiently and economically using absolute filters.