Water contamination in hydraulic oil can cause harmful effects. The water reduces the oil’s viscosity and lubricating function and water does not work in elastohydrodynamic lubrication. What’s worse, water in hydraulic oil will cause corrosion and metal fatigue and form sludge. Oxidation and hydrolysis shorten the oil’s lifespan. The negative consequences of water in a hydraulic oil leads to a shortened life span of pumps, valves and the oil itself.
Clean Oil Technology AB, a Swedish company, has developed the COT Oil Refiner System, a product that removes both free and bound water from hydraulic oils. The product, which is smaller and lighter in weight than competitive systems, can also save user costs. The COT Oil Refiner does not use filters or other materials, but the water is removed by energy alone—an evaporator operates at 75W.
A look at the various methods to eliminate water
Drainage: Many hydraulic and lubricating systems have large tanks to separate water and other contaminants. Air rises to the surface and water and other heavy contaminants sink to the bottom. Users can drain the free water through a valve at the lowest point of the tank.
Centrifugation: Water is separated from other oils by centrifugal power. The method removes part of the emulsified water (depending on the relative stability of the emulsion), but the centrifugation does not remove the bound water. Centrifugal separation is suitable for continuous decontamination of liquids with large amounts of water; the method requires water with good demulsibility (oil/water separation). The disadvantage is high capital and maintenance costs and a great power requirement.
Absorbent filters: These filters remove free and emulsified water through the absorbent polymers or cellulose materials. Absorbent filters are not well suited for large quantities of water and cannot remove bound water or heavily emulsified water. One advantage is that they also remove particles, such as varnish, which are produced through the oxidation of the oil.
Vacuum: Oils is “dried” by exposing it to a vacuum in combination with little heat. A low pressure (a great deal of vacuum) will lower the boiling point of liquids, and at a raised temperature the water is distilled (boiled) and eliminated.
What governs how much vacuum and what temperature are necessary are the oil’s properties and the risk that the distillation process might also remove certain necessary molecules, such as certain additives. The advantage of the vacuum is that it also removes redeemed air which is also harmful for oil and systems.
COT Oil Refiner
This method is based on optimising the heat addition (without the risk of oxidation) to the oil to remove water molecules in order to break up molecular oil/water bonds with the support of a controlled air flow. The COT Oil Refiners technology removes bound water from the oil—within 48 hours of operation, ppm levels of 100 pm and lower are obtained. There is no risk of oxidation as the oil is never allowed to exceed 60° C (for bio-oils 55° C), which unfortunately sometimes occur with methods that boil away water with high operating temperatures, creating oxidation. Therefore, temperature control is key to achieving optimal purification of hydraulic oil. COT’s preheating of hydraulic oil with its special technology ensures an optimal temperature without the risk of oxidation.
Another important parameter for removing harmful water is the control of air flow through the evaporator. With the evaporator’s air control technology, this air control can be adapted for each individual customer to achieve continuous steady removal of released water molecules. Properly controlling the direction/temperature/humidity and velocity of the airflow has a major impact on the outcome.
“The cellulose systems and other systems based on energization that are currently on the market are very large, heavy units, which excludes installation in most hydraulic systems for mobile machinery and vehicles,” said Stephan Larsson, COT AB’s Marketing Manager. “The investment cost and filter costs may be additional obstacles to the installation of these systems. It is not possible to keep the filtration levels below 400 ppm in continuous operation with cellulose filters.
Larsson said that in many mobile systems, operators deliberately run high temperatures to obtain water evaporation, but this leads to oxidation of the hydraulic oil—and hence reduced productivity of the hydraulic system.
“The customised particulate filters that customers can add can be supplied with various micron requirements, however, not fewer than 3 microns, because refined purification risks destroying the oil’s additive package and quickly clog most filters,” he said.
Clean Oil Technology AB