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Unlock the Secrets of Varnish Mitigation: Improve Your Hydraulic Systems Performance Now

Rob Panzarella
Posted by Rob Panzarella on Jun 11, 2024 3:44:39 PM
Unlock the Secrets of Varnish Mitigation: Improve Your Hydraulic Systems Performance Now

When hydraulic systems start underperforming, it can be frustrating and time-consuming. What's the problem? Where do you even begin? The usual culprit is hydraulic varnish buildup. This sticky substance seriously reduces your equipment's efficiency and lifespan. Let's explore some effective strategies for mitigating varnish in hydraulic systems.

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The Problem with Varnish in Hydraulic Oil | Deep Dive into Varnish Formation | Strategies to Reduce Varnish Formation | Testing & Analysis | Powerful Varnish Mitigation Systems | Frequently Asked Question 


Key Takeaways

✔️ Hydraulic varnish buildup can disrupt lubrication, increase operating temperatures, and cause seal damage and leaks in hydraulic systems.

✔️  To reduce varnish formation, offline filtration, dewatering, and degassing should be used. Electrostatic discharge should also be prevented. Oil temperature should be monitored, and hydraulic systems should be periodically chemically cleaned and flushed.

✔️  Advanced technologies, such as resin-based filtration, cooling, and standalone varnish mitigation units, ensure effective varnish control and enhance system performance and longevity.

The Problem with Varnish in Hydraulic Oil

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Varnish is a sticky, dark residue that forms in hydraulic systems, much like a dark stain applied to wood. Composed of organic and polar compounds, varnish particles are less than one micron in size and are soluble in oil. These deposits typically form on cold metallic surfaces, leading to various operational issues. The main issue is that varnish disrupts the lubricating properties of hydraulic oil and hinders its flow, causing valves to stick and pumps to wear out faster. This buildup also increases operating temperatures, leading to potential seal damage and leaks.


Causes of Varnish Formation

Several things lead to varnish buildup including: 

Extreme Heat Oxidation: High operating temperatures accelerate oxidation, leading to varnish precursors.

Electrostatic Discharge (ESD): Sparking within lubrication systems can damage filter elements and system components. Learn more in our blog post, Electrostatic Discharge (ESD) in Hydraulic Systems.

Cavitation and Micro-dieseling: These phenomena cause localized high temperatures and pressures, promoting varnish formation.

Elevated Turbine Bearing Temperature: Higher bearing temperatures increase the likelihood of varnish deposits.

Changes in Base Oils: Transitioning from group one to group two and three oils has increased varnish problems due to differing bonding sites for varnish precursors.

Impact on System Performance


Varnish can have severe consequences on hydraulic systems, including elevated friction and temperature, which may lead to potential bearing wear and damage. Also, varnish buildup can damage sensor and filter elements, diminishing overall system performance. Additionally, varnish buildup reduces heat transfer efficiency, resulting in higher operational temperatures and accelerated oil degradation. That's why addressing varnish formation is critical to maintaining the efficiency and longevity of hydraulic systems.

  • Increased friction and temperature
  • Bearing wear and damage
  • Sensor and filter element impairment
  • Reduced heat transfer efficiency
  • Accelerated oil aging



Deep Dive into Varnish Formation

Understanding the formation of varnish is key to preventing and mitigating its effects.


Causes of Varnish Formation

Varnish forms through several mechanisms, including extreme heat oxidation, electrostatic discharge, cavitation, and micro-dieseling. Each process introduces varnish precursors into the hydraulic oil, which is then deposited on metallic surfaces. Learn more in our blog post, 6 Types of Hydraulic Fluid Contamination You Need to Know. 


Effects on Hydraulic System Performance

Varnish buildup can significantly reduce the efficiency and reliability of hydraulic systems. It increases friction, causes bearing wear, and reduces heat transfer effectiveness, leading to higher operational temperatures and accelerated oil degradation.

Dealing with an underperforming system? Contact us for application support. 



Strategies to Reduce Varnish Formation

Effective varnish mitigation involves a combination of techniques. Let's review: 

Offline Filtration

Using offline filtration systems can help remove varnish precursors before they form deposits. These systems operate independently of the main hydraulic circuit, ensuring continuous filtration.

Dewatering and Degassing

Removing water and gasses from hydraulic oil can prevent the conditions that lead to varnish formation. Dewatering units and vacuum degassers are effective tools for this purpose.

Avoiding Electrostatic Discharge

Implementing measures to prevent ESD, such as using conductive materials and grounding, can reduce the risk of varnish formation due to sparking.

Monitoring Oil Temperature

Maintaining optimal oil temperatures is crucial for minimizing oxidation and varnish formation. Cooling systems can help achieve this.

Chemical Cleaning and Flushing

Periodic chemical cleaning and flushing of hydraulic systems can remove existing varnish deposits and prevent further accumulation.


Testing & Analysis

📝 Several tests can detect varnish presence and concentration in hydraulic oil:

Membrane Patch Colorimetry (MPC): MPC measures the color intensity of a filtered oil sample, indicating varnish levels.

Particle Counting at Different Temperatures: This test identifies the size and quantity of particles in the oil, providing insights into varnish formation.

Ultracentrifuge: Separates varnish particles from the oil for detailed analysis.

Quantitative Spectrophotometric Analysis (QSA): Measures the concentration of varnish precursors in the oil.

Electrical Conductivity: Indicates the presence of varnish by measuring the oil's electrical properties.


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Powerful Varnish Mitigation Systems

Several advanced technologies and equipment are available for varnish mitigation. Review below or learn more in our blog post, Three HYDAC Solutions for Hydraulic Varnish Removal. 


Resin-Based Filtration Systems

These systems use specialized resin materials to capture varnish precursors, effectively preventing their formation.

Cooling and Fine Filtration

Combining cooling systems with fine filtration units enhances varnish mitigation by removing precursors and maintaining optimal oil temperatures.

Varnish Mitigation Units

Standalone units are specifically designed to address varnish issues, employing a combination of filtration, dewatering, and cooling techniques.

Hydraulic varnish is a significant challenge for system operators, industrial maintenance specialists, and fluid chemists. You can maintain peak system performance and longevity by understanding its causes, impacts, and mitigation strategies. Learn more in our on-demand webinar, Varnish Mitigation 101, or reach out for expert support in hydraulic varnish mitigation.


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Frequently Asked Questions

What is hydraulic varnish, and why is it a problem?

Hydraulic varnish is a dark, sticky residue composed of organic and polar compounds. It forms in hydraulic systems on cold metallic surfaces. It disrupts the lubricating properties of hydraulic oil, hinders its flow, increases operating temperatures, and may cause damage and leaks.


What causes varnish formation?

Varnish formation can be caused by various factors including extreme heat oxidation, electrostatic discharge, cavitation, microdieseling, elevated turbine bearing temperature, and changes in base oils.


What impact does varnish have on hydraulic systems performance?

Varnish can reduce the efficiency and reliability of hydraulic systems by causing increased friction, bearing wear, sensor and filter element impairment, reduced heat transfer efficiency, and accelerated oil aging.


What are some strategies to reduce varnish formation?

Strategies for varnish mitigation include offline filtration, dewatering, degassing, avoiding electrostatic discharge, monitoring oil temperature, and periodic chemical cleaning and flushing of the hydraulic system.



Topics: Hydraulics, Maintenance, HYDAC, Fluid Cleanliness

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