Best Methods to Remove Water Contamination from Hydraulic Oil

How to Remove Water Contamination from Hydraulic Oil

Water contamination in hydraulic oil is a serious and common issue that can cause corrosion, cavitation, pump damage, and valve failure. Once detected, immediate action is required.

The correct water removal method depends on the severity of contamination, system type, and operating conditions.

Basic Principles for Treating Water-Contaminated Hydraulic Oil

1. Immediate Shutdown

If oil appears milky, emulsified, or heavily turbid, stop the system immediately to prevent component damage.

2. Identify and Eliminate the Water Source

Common causes include:

• Oil cooler leakage

• Damaged seals or pump shafts

• Poor or missing desiccant breathers

• Condensation from temperature changes

Always remove the root cause before oil treatment.

3. Assess the Degree of Contamination

Hydraulic Oil Water Removal Methods

1. Settling (Gravity Separation)

Suitable for: Free water only

• Use a conical-bottom or settling tank

• Heat to 60–70°C (within oil limits)

• Settle for 24–48 hours, then drain water

Limitation: Cannot remove dissolved or emulsified water

2. Vacuum Dehydration (Most Effective)

Principle: Oil is heated under vacuum (50–80°C) to evaporate free, dissolved, and emulsified water.

Advantages:

• Removes all water forms

• Preserves oil properties

• Can operate online

• Restores cleanliness to NAS 6–8

Applications: Precision systems, power plants, large hydraulic systems

3. Centrifugal Separation

• Separates oil, water, and solids by density

• Effective for high water and particle content

• Limited performance on strong emulsions and high cost

Common use: Marine and metallurgical systems

4. Coalescing Filtration

• Coalescing filters merge small water droplets for separation

• Effective for moderate emulsification

• Filter elements require regular replacement

5. Adsorption Dehydration

• Uses silica gel or molecular sieves

• Suitable for trace moisture removal

• Requires close monitoring to prevent secondary contamination

Post-Treatment Testing and Recovery

1. Oil Quality Verification

• Water content: Karl Fischer

  • Target <500 ppm (precision systems <200 ppm)

• Cleanliness: Particle counting

• Viscosity & acid number: Confirm no severe oxidation

2. System Cleaning

• Flush tanks and pipelines if oil was heavily emulsified

• ｒｅｐｌａｃｅ all hydraulic filter elements

Prevention Measures

• Conical-bottom oil tanks with regular drainage

• Desiccant breathers on reservoirs

• Routine seal inspection

• Maintain lower water-side pressure in oil coolers

• Install online moisture or dew-point sensors

Important Warnings

• Do not operate long-term with water-contaminated oil

• Do not heat oil above 80°C

• Use proper safety and explosion-proof equipment

For severely contaminated or complex systems, professional on-site oil purification using mobile vacuum dehydration units is recommended.
For critical equipment, permanent online dehydration systems provide the most cost-effective long-term solution.