Being around hydraulic systems for any amount of time causes side-effects – and one of the nastier ones is knowing just how distressing murky oil can be. Most technicians in the field know that cloudy oil means contaminants have found their way into your fluid – and the main culprit is one we’ll never be completely rid of as long as we live on Earth — water. Of course, all hydraulic oil contains trace amounts of water, but too much water can mean increased internal corrosion and eventual hydraulic failure or inefficiency. Today, we’ll discuss methods of removing the water stockpile in your system’s oil and how that might benefit you and your machines in the long term.
Understanding The Saturation Level
Since there will always be water in your hydraulic oil (you can never be COMPLETELY rid of it) it’s important to know how much is too much. Technicians use the term “saturation level” to refer to the amount of water a given mineral hydraulic oil will dissolve into its molecular chemistry. This level determines the amount of water a particular system can let on before experiencing significant performance issues. Generally, the saturation level rests somewhere between 200 ppm (parts-per notation) and 300 ppm at a system operational temperature of 68°F (20°C). Given this general figure, we can guess that any cloudy oil has water levels that reach upwards of 200-300 ppm. Beyond this level, water begins to become a contaminant, rather than an integral part of the system. And so, we make moves to remove it. To do that, we could use:
Polymeric Filters
These are great for removing small amounts of water from a system. They work by employing a super-absorbent polymer which swells on contact with water. The polymer is imbedded within a media which is able to trap the water and allow for manual removal later. Keeping water within certain limits (whether they be set by the operator or by the manufacturer) is what polymeric filters do best, and they should be used only when the risk of water contamination is determined to be low.
Vacuum Distillation
Making use of vacuum and heat might seem the obvious go-to for getting rid of water, in general, but the distillation process is delicate and requires precise attention to temperature monitoring and control. Given a sample of 25 inches Hg, water boils beginning at 133°F – anything less and the water will remain in the system, anything (excessively) more and the oil may begin to change state or the structure of the system may be warped or altered. If precise temperatures can be maintained with help from a mechanism, vacuum distillation can be used to remove much of the unwanted water from your system. In addition, other unwanted high vapor-pressure contaminants such as solvents, refrigerates, or fuels can be effectively removed from a system by vacuum distillation.
Headspace Dehumidification
By forcing water vapor into the reservoir headspace, it can be easily removed by a dehumidifier. This method is particularly useful when dealing with pressure sensitive systems. Vapor is much more simple to remove from a system, especially since – in the gaseous state – the water is separated from the oil on the molecular level. The dehumidication process itself is relatively inexpensive and removes much of what you want gone – such as emulsified, free, and dissolved water.
Of course, being rid of water is only a secondary concern in the hydraulic world. The always-present risk of air contamination and filter failure will likely occupy the majority of any hydraulic operator’s allocated repair and service time. But, certainly, methods of addressing this sort of contamination should always be fresh in your mind. The time will come when you’ll need that knowledge – be sure and mark the day when it does.