Dry oil is happy oil, and because I have never seen a lottery-winning oil on anti-depressants while watching The Wizard of Oz, so I stand by my claim. When I say dry, I’m not referring to free standing water, as you can reel off without help from me the reasons metal components don’t like pools of water. Humidity is not just a quality of air, but also of oil.
Water vapor is the gas phase of H2O, and just like it is all around you as you read this, it is partially saturated within hydraulic oil as well. I say it is partially saturated, because a level of water within hydraulic oil at saturation point or above would cause free water. Free water in hydraulic oil can manifest itself as localized dew formations, or in extreme cases, emulsion with the oil which creates the easily recognizable milky appearance.
A little bit of humidity is okay for a hydraulic system. However, as the humidity within the oil increases, it not only increases the oxidation rate of the oil itself, but the oxidation rate of the metal components in the system. Oxidation of the oil decreases its tendency to provide benevolent qualities, like lubrication. Lubrication is good, mmm’kay.
So, water is bad, and we can all agree on that unless you’re running a system with oil emulsion or water-glycol; otherwise, water is still bad (mmm’kay). So what can you do to keep your oil dry? Some of you may put to use a water-removing filter element, and although they’re decent at removing free water, they have a harder time with humidity.
The best method of water removal, as far as I’ve seen and I’d love to hear about other ways, is with vacuum dehydration. The idea with vacuum dehydration is to heat the oil at the same time as a vacuum is applied. When water boils, it turns to vapor. Under a vacuum, water boils at a lower temperature. We can heat the oil under vacuum to a point where it is boiled off and removed without damaging the hydraulic oil. The best method of creating dry oil is in preventing it, but this method is a great method to save expensive oil should it become contaminated with water.