Hydraulic oil becomes cloudy when it is contaminated with water above its saturation level. That is the amount of water that can be dissolved in hydraulic oil and is typically 200 - 300 ppm for mineral hydraulic oil measured at 68°F (20°C).
Water in hydraulic fluid
● Reacts with some additives to form corrosive by-products which corrode some metals.
● Leaves critical surfaces vulnerable to wear and corrosion due to reduced lubrication film-strength.
● Clogs filters and reduces the filterability of the oil.
● Increases air entrainment.
● Increases cavitation occurrence.
Water removal methods
● Polymeric filters- H20 causes the polymer to swell, trapping water within the media. Best suited for removing small amounts of H20 or H20 contamination within allowable limits.
● Vacuum distillation - Water boils at 133°F (56°C) at 25 inches Hg. At this temperature water can be removed without damage to the oil or its additives.
● Headspace dehumidification- Circulating and dehumidifying air from the reservoir headspace causes water in the oil to migrate to the dry air. It is then removed by the dehumidifier.
● Changing out the oil - Depending on system size, changing the oil may be more cost-effective than using any of the above methods of water removal.
Prevention is best cure and is cheaper than removing H20 from the oil.
Standard breather caps on hydraulic reservoirs are a major source of H20 in hydraulic power units. Replacing the standard breather cap with a hygroscopic breather will eliminate the moisture ingress and keep contamination particles out of the reservoir.
Water in hydraulic fluid
● Reacts with some additives to form corrosive by-products which corrode some metals.
● Leaves critical surfaces vulnerable to wear and corrosion due to reduced lubrication film-strength.
● Clogs filters and reduces the filterability of the oil.
● Increases air entrainment.
● Increases cavitation occurrence.
Water removal methods
● Polymeric filters- H20 causes the polymer to swell, trapping water within the media. Best suited for removing small amounts of H20 or H20 contamination within allowable limits.
● Vacuum distillation - Water boils at 133°F (56°C) at 25 inches Hg. At this temperature water can be removed without damage to the oil or its additives.
● Headspace dehumidification- Circulating and dehumidifying air from the reservoir headspace causes water in the oil to migrate to the dry air. It is then removed by the dehumidifier.
● Changing out the oil - Depending on system size, changing the oil may be more cost-effective than using any of the above methods of water removal.
Prevention is best cure and is cheaper than removing H20 from the oil.
Standard breather caps on hydraulic reservoirs are a major source of H20 in hydraulic power units. Replacing the standard breather cap with a hygroscopic breather will eliminate the moisture ingress and keep contamination particles out of the reservoir.
