Dealing With Water In Your Hydraulic Oil

If your hydraulic oil looks cloudy or milky, it’s usually a sign of water contamination. This reduces efficiency, accelerates wear, and can significantly shorten the life of key components — from your hydraulic pump to critical valves such as Cetop 7 solenoid valves.

Why does hydraulic fluid become cloudy?

A small amount of water in hydraulic oil may not immediately cause visible issues. However, once the amount of water exceeds the oil’s saturation level, the oil becomes cloudy.

The saturation level is the amount of water that can be dissolved in oil before it separates and becomes noticeable. For common mineral hydraulic oil, this level is typically 200–300 ppm at around 20°C.

What cloudy oil means

If your oil appears cloudy, it likely contains at least 200–300 ppm of water. At this point, contamination is no longer minor — it is actively affecting performance and protection.

Why is water contamination bad for a hydraulic system?

Water in hydraulic oil can severely damage both the system and its individual components. Key risks include:

Additive depletion & corrosion: Water depletes protective additives and reacts to form corrosive by-products that attack metal surfaces — including pumps, tanks, and valves such as Cetop 7 solenoid valves.
Reduced lubrication strength: Water weakens the oil’s lubricating properties, leaving critical internal surfaces vulnerable to wear and corrosion.
Filter blockage: Water contamination can clog filters, potentially leading to dangerous pressure build-up.
Increased air entrainment: Water raises the likelihood of air entering the system.
Cavitation risk: Increased chances of cavitation and other damaging hydraulic events.

Why quick action matters

Left untreated, water contamination can dramatically shorten component life and increase maintenance costs. Early detection and correction are essential.

How can I remove water from my hydraulic system?

There are three common methods used to remove both free and dissolved water:

1) Polymeric filters

These resemble conventional filters but use a super-absorbent polymer material. The polymer absorbs water, swells, and traps it within the filter.

Best for: removing smaller volumes of water and maintaining contamination below a set threshold.

2) Vacuum distillation

This method uses heat and vacuum. At approximately 25 inches Hg, water boils at around 56°C, allowing it to be removed without damaging the oil or its additives.

Best for: systems with higher levels of contamination.

3) Head space dehumidification

This method circulates and dehumidifies air in the reservoir head space. Moisture migrates from the oil into the dry air and is gradually removed.

Prevention is always better

Preventing water ingress is far more cost-effective than removing it. Good sealing practices, proper storage, and regular fluid checks help protect all hydraulic components — including sensitive valves like Cetop 7 solenoid valves.