Deep-clean hydraulic oil.
Extend oil service life.
Continuously removes fine particles, sludge, resin and oxidation products from non-conductive hydraulic and lubricating oils, helping reduce equipment failures and extend oil service life.
Continuous cleaning. Less maintenance.
Left: oil sample before cleaning
The oil contained contaminants that conventional filters could not adequately capture, resulting in frequent hydraulic-system faults and oil changes.
Right: after two weeks of bypass electrostatic cleaning
During subsequent observation in this case, the system remained fault-free and no further oil changes were required because of contamination.
How Does the FRIESS EFR Deep-Clean Hydraulic Oil?
0.01 μm
10–20 years
Up to about 70%
Designed for industrial oils with water content below 500 ppm, the DSD uses electrostatic deep cleaning to remove fine particles, sludge and oxidation products, helping extend oil and equipment life.
Electrostatic Oil Cleaner Applications
Reliable Control and Actuation of Hydraulic Systems
Reduce Valve Sticking and Unplanned Hydraulic-System Downtime
How FRIESS EFR Electrostatic Oil Cleaners Deep-Clean Hydraulic Oil
Article Navigation
SECTION 01 | How Contamination Damages Hydraulic Systems
How Clean Hydraulic Oil Protects Reliable Equipment Operation
Fine particles in hydraulic systems cause wear and erosion and also accelerate oil oxidation. Continuously removing particles, sludge, varnish and deposits helps reduce failures and extend the service life of the oil and precision components.
1–4 µm
Typical lubricating-film thickness
10–20 years
Long-term oil-service example
Approx. 70%
Potential reduction in failures
01 · WEAR
Wear
Particles entering lubrication clearances break down the oil film, damage pumps, valves and moving surfaces, and generate additional wear particles.
02 · EROSION
Erosion
High-speed oil flow carries particles into valve edges and nozzles, gradually cutting grooves that reduce control accuracy and increase internal leakage.
03 · OXIDATION
Oxidation
Contaminant particles catalyse oil oxidation and promote varnish, deposits and sludge, causing valves to stick and respond slowly.
Which Hydraulic Faults Can Oil Contamination and Ageing Cause?
Faults associated with deteriorated or contaminated oil can occur throughout a hydraulic system. Components with tight clearances, moving sealing surfaces or narrow control passages are particularly sensitive. Use the following as an initial troubleshooting guide; confirm the cause through on-site checks and oil analysis.
Hydraulic pump
Wear, loss of performance or seizure
Contamination particles, water, unsuitable viscosity or aged oil
Valves / control blocks
Sticking valves, delayed switching or leakage
Particles, deposits and resinous residues
Proportional / servo valves
Inaccurate or jerky movement, or failure
Especially sensitive to fine particles and resinous deposits
Hydraulic cylinders
Stick-slip motion, internal leakage or seal wear
Particles, water or chemically aged oil
Hydraulic motors
Loss of speed, wear or unusual noise
Oil contamination or inadequate lubrication
Filters
Rapid clogging, high differential pressure or bypass opening
High particle loads, sludge and oil-ageing products
Throttle valves / small passages
Blockages, changes in flow, enlarged openings or wear
Abrasive particles and deposits
Seals
Leakage, embrittlement or swelling
Incompatible oil, excessive temperature or chemical ageing
Pipes / coolers
Deposit build-up or reduced heat transfer
Oxidation products and sludge
Hydraulic tank
Sludge, corrosion or foaming
Water, air and oil-ageing products
Sensors / pressure switches
Incorrect readings or delayed response
Deposits and contamination
Four Common Oil-Related Causes of Hydraulic Problems
Particle contamination
Metal wear debris, dust and other solid particles can increase wear in hydraulic pumps and cylinders and cause valves to stick. Continuous contamination control helps maintain reliable hydraulic-system operation.
Water in hydraulic oil
Water can cause corrosion, impair lubrication and accelerate oil ageing. If water content is elevated, assess dehydration requirements against oil-analysis results and equipment specifications. Learn more about FRIESS vacuum oil purification and dehydration.
Oil ageing and oxidation
Oxidation produces acidic compounds, sludge and varnish-like deposits. Varnish and resinous residues can affect precision valves, causing sticking and delayed response.
Unsuitable viscosity
Oil that is too thin can increase internal leakage and wear. Oil that is too thick can cause poor suction, higher pressure losses and sluggish movement. Check oil selection and operating temperature: cleaning cannot replace the correct oil grade.
Electrostatic cleaning primarily targets particles and certain soft contaminants. Excess water, unsuitable viscosity or irreversible chemical degradation require separate assessment of dehydration, oil selection or oil replacement.
SECTION 02 | Cleanliness and Oil Requirements
Oil Cleanliness Must Meet System Requirements
Oil Quality and Equipment-Warranty Requirements
Meeting the specified oil cleanliness is essential for technical reliability and may also affect the equipment warranty. Some manufacturers may reject warranty claims if the hydraulic oil does not meet their cleanliness requirements.
Select oil-purification equipment capable of continuously maintaining the target cleanliness class and verify performance through regular oil analysis.
More information: hydraulic-oil analysis and cleanliness-class assessment.
Hydraulic Oil Purification Basics
Maintenance Checklist
11 Ways to Reduce Failures and Operating Costs
For routine inspection and preventive maintenance
01
Follow the maintenance intervals and requirements specified by the manufacturer
02
Have trained personnel perform and document maintenance
03
Check oil condition regularly through oil analysis
04
Replace hydraulic oil only when its chemical condition is out of specification
05
Prevent water ingress and dewater the oil when necessary
06
Keep seals and hoses intact and replace damaged parts promptly
07
Keep the working environment clean to reduce contaminant ingress
08
Do not allow the oil level to fall below the specified minimum
09
Store hydraulic oil in clean, sealed and suitable containers
10
Use clean equipment and filter new oil during filling and top-up
11
Inspect the filtration system and oil cleanliness regularly
SECTION 03 | Conventional Hydraulic Oil Filtration Methods
Suction Filters
Pressure Filters
Return-Line Filters
Depth Filters
Screen Filters
Offline and Bypass Purification
SECTION 04 | EFR Electrostatic Purification Principle
Capturing Contaminants with an Electrostatic Field Instead of Fine Pores
Pore Size Determines Retention Capability
Regenerative Oil Purification
EFR continuously removes oxidation-promoting ultrafine particles and existing soft deposits, slowing oil ageing and helping restore oil performance.
Four Core Advantages of FRIESS EFR
SECTION 05 | Maintenance, Sustainability and Economy
Clean, Large-Area Collector Media
Contaminants Are Captured Visibly
How Does Oil Purification Save Oil and Protect Resources?
Extend Oil Life While Reducing Resource Consumption
SECTION 06 | Selection Guide and Frequently Asked Questions
More Than 50 Years of FRIESS Industrial Oil-Purification Experience
Filtration Method
Oil Volume and Treatment Capacity
Target Cleanliness
Contaminant Type
Installation and Maintenance
Why Is Maintenance Simpler?
Clear, fast maintenance procedures help reduce labour and downtime costs. The FRIESS EFR display indicates operating time and maintenance intervals for timely contamination checks. Collector media and electrodes are readily accessible, and the hydraulic system can remain in operation during servicing. High contaminant capacity allows a typical inspection interval of about 2,000 operating hours; the actual interval depends on the contamination load.
How Do You Select the Right Filtration Combination?
The optimum filtration solution depends on the specific system. Most hydraulic systems combine several filtration methods to achieve the target cleanliness. Follow the oil and equipment manufacturers’ requirements when selecting equipment and setting maintenance intervals.
Conventional filters can control hard particles above a certain size but often cannot remove the ultrafine particles that accelerate oil ageing or soft contaminants such as varnish and resin. This is the principal application advantage of FRIESS EFR electrostatic oil purification.