How to Remove Water from Hydraulic Oil: A Comprehensive Guide

Water in hydraulic oil is a big problem that can affect the performance and life of hydraulic systems. Whether due to condensation, leaks, or poor maintenance, water can cause corrosion, reduced lubrication, and wear on system components. To keep your system running at its best you need to remove water from hydraulic oil.

In this article we will go through 8 methods to remove water from hydraulic oil, each method’s specifications, effectiveness, and practical considerations. For a full system clean consider combining these methods with professional solutions like “Cleaning & Flushing a Hydraulic System” services and “Oil Flushing System” from INVEXOIL.

How to Remove Water from Hydraulic Oil?

There are 8 methods to remove water (dehydration) from hydraulic oil:

• Gravity Separation
• Heat Application
• Centrifugation
• Absorption Filters
• Vacuum Dehydration
• Coalescence Filters
• Absorbent Polymer Separation
• Membrane Separation

 

1. Gravity Separation

Method Type: Simple Physical Separation

Material/Equipment: Settling Tanks or Containers

Effectiveness: Low (suitable for minor contamination)

Time Required: Hours to Days

How Gravity Separation Works:

Gravity separation relies on the density difference between water and hydraulic oil. The contaminated fluid is left undisturbed in a container, water will settle at the bottom due to its higher density. Water can be drained from the bottom of the tank.

Before and After Hydraulic Oil Condition Using Gravity Separation Method:

• Before: Fluid appears milky or cloudy due to water contamination.
• After: Some water is removed, but emulsified water remains, and complete dehydration is not achieved.

Pros:

• Simple and cost-effective
• No specialized equipment required

Cons:

• Ineffective for emulsified water
• Time-consuming

 

2. Heat Application for Dehydrating Hydraulic Fluid

Method Type: Thermal Evaporation

Material/Equipment: Heat Gun, Hair Dryer, or Industrial Heater

Effectiveness: Moderate

Temperature: 100°C or Higher

How Heat Application Works:

Heat applied to hydraulic oil causes water to evaporate. The fluid is heated above water’s boiling point and moisture will turn into vapor and escape from the oil.

Before and After Hydraulic Oil Condition Using Heat Method:

• Before: Fluid contains visible water contamination.
• After: Reduced water content, but risks of damaging the oil properties remain if overheated.

Pros:

• Relatively simple process
• Can be done with basic equipment

Cons:

• Risk of overheating and damaging the oil
• Not suitable for large volumes

 

3. Centrifugation (Centrifugal Separators of Removing Water from Hydraulic Oil)

Method Type: Mechanical Separation

Material/Equipment: Centrifuge

Effectiveness: High for Free Water, Moderate for Emulsified Water

Speed: High Rotational Speeds

How Centrifugal Separator Works:

Centrifugation involves spinning the hydraulic fluid at high speed to separate water based on density difference. The centrifugal force pushes denser water particles outwards where they can be collected and removed.

Before and After Hydraulic Oil Condition Using Centrifugal Separators:

• Before: Fluid contains both free and emulsified water.
• After: Free water is effectively removed, but some emulsified water may remain.

Pros:

• Effective for removing free water
• Fast process

Cons:

• Requires specialized equipment
• Less effective for emulsified water

 

4. Absorption Filters for Dehydrating Hydraulic Fluid

Method Type: Absorptive Separation

Material/Equipment: Silica Gel, Molecular Sieves

Effectiveness: High for Moderate Water Levels

Capacity: Varies by Filter Size and Material

How Absorption Filters Work:

Absorption filters use absorbent materials to trap water molecules as the fluid passes through the filter. These filters can be installed inline for continuous water removal.

Before and After Hydraulic Oil Condition Using Absorption Filters:

• Before: Fluid with water contamination.
• After: Clear, dry fluid with improved performance and longevity.

Pros:

• Continuous operation
• Effective for moderate water levels

Cons:

• Filter replacement is required
• Less effective for high water volumes

 

5. Vacuum Dehydration for Dehydrating Hydraulic Fluid

Method Type: Vacuum-Induced Evaporation

Material/Equipment: Vacuum Dehydrator

Effectiveness: Very High

Vacuum Pressure: Low (e.g., 25-29 inHg)

How Vacuum Dehydrating of Hydraulic Oil Works:

Vacuum dehydration reduces water’s boiling point by creating a vacuum environment. The hydraulic fluid is exposed to this vacuum and water will evaporate at lower temperature, even below 100°C.

Before and After Hydraulic Oil Condition in Vacuum Dehydration Method:

• Before: Fluid contains free, dissolved, and emulsified water.
• After: Virtually all water is removed, resulting in clear, dry fluid.

Pros:

• Highly effective
• Safe for oil properties

Cons:

• Expensive equipment
• Requires professional setup

Related Article: What is Vacuum Dehydration Oil Purification Systems? Key to Oil Purity

6. Coalescence Filters to Remove Water from Hydraulic Oil

Method Type: Coalescent Separation

Material/Equipment: Coalescing Elements

Effectiveness: High for Free Water

Flow Rate: Depends on Filter Design

How Coalescence Filters Work:

Coalescence filters force water droplets to merge into larger drops through a coalescing medium. These larger drops are then separated and removed from the fluid.

Before and After Condition of Hydraulic Oil Filtering by Coalescence:

• Before: Fluid with dispersed water droplets.
• After: Free water is effectively removed, restoring fluid clarity.

Pros:

• Effective for free water
• Continuous operation

Cons:

• Requires regular maintenance
• Ineffective for emulsified water

 

7. Absorbent Polymer Separation for Dehydrating Hydraulic Fluid

Method Type: Polymer-Based Absorption

Material/Equipment: Superabsorbent Polymers (SAPs)

Effectiveness: High for Low-Level Moisture

Capacity: Can Absorb up to 100,000% of its Weight in Water

How Absorbent Polymer Separation Works:

Superabsorbent polymers (SAPs) attract and hold water molecules, swelling as they absorb water. These polymers can be added to the fluid or used in filters.

Before and After Condition of Hydraulic Oil Using Absorbent Polymer Separation:

• Before: Fluid with water contamination.
• After: Clear, dry fluid with enhanced system efficiency.

Pros:

• Highly effective for low-level moisture
• Easy to use

Cons:

• Not suitable for large-scale operations
• Polymers need regular replacement

 

8. Membrane Separation

Method Type: Filtration-Based Separation

Material/Equipment: Semi-Permeable Membrane Filters

Effectiveness: High for Dissolved and Emulsified Water

Capacity: Varies by Membrane Design and Pore Size

How Membrane Separation  Works:

Membrane separation uses semi-permeable membranes to filter out water molecules from hydraulic oil. The membrane allows the oil to pass through while blocking water and other impurities. This method is very precise and effective for removing dissolved and emulsified water.

Before and After Condition of Hydraulic Oil Using Membrane Separation Method:

• Before: Fluid contains dissolved and emulsified water.
• After: Water content is significantly reduced, resulting in clear and dry fluid.

Pros:

• Precise water removal
• Effective for dissolved and emulsified water

Cons:

• Expensive equipment
• Requires regular maintenance and cleaning of membranes

Table: Methods of Water Removal from Hydraulic Oil Comparison

Method	Effectiveness	Best for	Equipment Required	Pros	Cons
Gravity Separation	Low	Minor Contamination	Settling Tanks	Simple, Cost-Effective	Time-Consuming, Ineffective for Emulsified Water
Heat Application	Moderate	Small Volumes	Heat Gun, Industrial Heater	Simple Process	Risk of Overheating
Centrifugation	High (Free Water)	Free Water	Centrifuge	Fast Process	Expensive Equipment
Absorption Filters	High	Moderate Water	Silica Gel, Molecular Sieves	Continuous Operation	Filter Replacement Required
Vacuum Dehydration	Very High	All Water Types	Vacuum Dehydrator	Highly Effective	Expensive Equipment
Coalescence Filters	High (Free Water)	Free Water	Coalescing Elements	Effective for Free Water	Regular Maintenance Required
Absorbent Polymer Separation	High	Low-Level Moisture	Superabsorbent Polymers	Easy to Use	Not Suitable for Large-Scale Operations
Membrane Separation	High	Dissolved and Emulsified Water	Semi-Permeable Membrane Filters	Precise Water Removal	Expensive Equipment

Conclusion

Removing water from hydraulic oil is a must do maintenance to keep your hydraulic system running at its best. Different methods like gravity separation, heat application, centrifugation and membrane separation have different level of effectiveness depending on the type and amount of water contamination. For full solutions consider combining multiple methods.

Combining professional solutions like Cleaning & Flushing a Hydraulic System services and Oil Flushing System from INVEXOIL will further increase system reliability and long term hydraulic oil maintenance. Proper water removal will prevent equipment failure, reduce maintenance cost and improve overall system efficiency.