Your oil is wet. No, I didn’t skip 8th grade science class, where you learn how oil and water don’t mix. Okay, so it mixes a bit, if you agitate it enough, but then separates nicely with oil floating atop water. Your hydraulic fluid likes water as much as olive oil likes a bottle of Tapwater Springs, but in only the rarest of circumstances does enough free water intrude upon your hydraulic system to create lakes in your reservoir.

Wet hydraulic oil is the same as damp air, in that the water molecules are partially dissolved in the oil, like humidity in the air. For the most part, “damp” hydraulic oil is no real concern. Most of the time, the saturation level of water is low enough to cause little concern. But in some cases, excessive water contamination does occur, where the “humidity” of the oil reaches the saturation point. When water saturation reaches 100%, droplets can “rain” out of the oil—causing pools, puddles or other areas of localized water.

Water in your oil can cause a few problems to your hydraulic system. The most common problem with humid oil is that the increased water content accelerates the oxidation rate of the fluid, lowering its life expectancy. Not only does water increase the oxidation rate of the oil itself, but you may have noticed the majority of hydraulic pumps, valves and actuators are made from iron and steel, both of which oxidize quickly in the presence of water. Not only does this cause corrosion of the internal hydraulic components, but also the corrosion itself its a form of contamination when it is released into the system.

Should water saturation levels become so high that you experience free water, you’re in for a world of hurt. When water struts around your hydraulic system acting like it owns the joint, it displaces oil everywhere it exists. Water makes a terrible lubricator, and everywhere there is no oil, you are risking rapid metal-to-metal wear. And where water loiters, such as in localized, um … locations, the corrosion rate is further exacerbated. In the worst of cases, pooled water can freeze, and subsequently damage components.

As you can imagine, it’s best just to avoid water contamination. The bad news is that water can be the most difficult contamination to control. You can purchase inexpensive water-absorbing filter elements, but they’re typically terrible filters that happen to suck up only free water. They can’t do anything to dry out the oil and remove humidity. If you are in the need for water absorbing elements, you’re already in a world of hurt, because you’ve let it go too far, like a viral Twitter party. That being said, throwing a few $50 filters at the problem could be cheaper than replacing a few grand worth of hydraulic oil.

I’m not going to patronize you by pointing out you simply should avoid getting water into your hydraulic system. But should you accidentally contaminate your expensive oil with water, aside from from changing it entirely, I’m going to tell you about the most effective way to remove water. The solution involves going back to science class, so have a seat and pay attention.

We know water will boil at a hundred degrees Celsius, or about 212° F. I’ll concede, you probably shouldn’t heat your hydraulic oil up to this intensity (as explained earlier), but we do we remember from class? Well, if you live in Denver, your boils almost 10° cooler. This occurs because air pressure is lower, and it takes less heat energy for the molecules to break their bond, evaporating the water sooner than at sea level.

Bonus points for observing that lower ambient pressure means lower boiling point. So what if we could take advantage of this effect, and lower the boiling point of water that is saturated within oil? It’s probably asking too much to bring your machine to Denver just to dry your oil, so what if we can lower the pressure surrounding the oil? Most of you have a vacuum in your home, which is a great device for lowering pressure. This is where the vacuum dehydrator comes in; it’s a machine that subjects oil to a vacuum, and then heats it up a bit. Less heat is required to cause the saturated oil to boil away its water, and a side bonus is that the vacuum sucks away all the humid air.

The problem with vacuum dehydrators is they’re expensive, some in the realm of twenty large. Most often, your best bet is to rent them, which you can do at your local fluid power distributor. They’re the most effective way to remove saturated water (although your best bet is still to avoid water altogether). If you can’t get your hands on a dehydrator, you can always pack up shop and move to Denver.

Also, check out “What is hydraulic fluid conditioning – part 1.”

Also, check out “What is hydraulic fluid conditioning – part 2.”