The performance, life and reliability of hydraulic components is acutely sensitive to the quality and maintenance of the hydraulic ﬂuid used in the system. That is why it pays to use a high- quality hydraulic ﬂuid, inspect ﬂuid samples at regular intervals, and practice regularly scheduled preventive maintenance. By observing these simple precautions system downtime will be reduced and the overall life of the hydraulic system will be increased. This document provides guidelines for the selection and care of hydraulic ﬂuid in high-performance hydraulic systems.
High-performance hydraulic systems require very clean oil to maximize performance and extend the life of system components. While less sophisticated hydraulic systems may function acceptably with lower levels of oil cleanliness, high-performance hydraulic equipment will “silt up” and perform erratically when subjected to particulate levels that are greater than an ISO 4406 rating of 16/13/9. Servo valves must operate smoothly and predictably to deliver the tightly regulated pressures and ﬂuid ﬂow for which they are designed.
Hydraulic ﬂuid contamination and deterioration are normal consequences for most hydraulic systems. Failure to adequately remove contaminants, or to change hydraulic ﬂuid before severe ﬂuid breakdown occurs, will lead to poor system performance. The most common hydraulic ﬂuid contaminants are entrapped air and water, along with particles of metal, rubber or dirt. To maintain clean hydraulic ﬂuid, samples must be taken regularly and appropriate mitigation should be immediate.
Fluid deterioration might more appropriately be called “additive deterioration.” Additives give the oil its particular characteristics—and because these additives are most susceptible to chemical and physical change, their deterioration is what leads to ﬂuid breakdown.
Fluid deterioration is often caused by operation at high temperatures. Fluid reservoir temperatures are best kept below 140° F (60° C). To keep ﬂuid operating temperatures within the acceptable range of 100-125° F (38-52° C), standard hydraulic power units are equipped with full-motor-horsepower heat exchangers, over-temperature interlocks and temperature controls.
Regular monitoring and maintenance of the hydraulic ﬂuid promotes the maximum operating performance and service life of the servo hydraulic system and its components. Two speciﬁc items must be checked regularly contaminants in the ﬂuid and the ﬂuid’s chemical makeup. Fluid sampling and analysis is the best way to determine whether the ﬂuid and ﬁlters should be changed. Fluid analysis will provide an accurate viscosity reading while detecting speciﬁc contaminants such as water or foreign particles. It can also be used to check the chemical makeup of the ﬂuid to identify whether the additive package is still able to perform as it was originally designed.
A correct evaluation of the contaminants in the hydraulic system is important. When the contaminating material is identiﬁed, its source can be investigated to prevent future contamination.
Many ﬁlter manufacturers offer services, giving special attention to particle counts and speciﬁc contaminants..
Looking at and smelling hydraulic ﬂuid is the simplest and most effective way to determine the ﬂuid’s condition. Clean ﬂuid is amber in color. A milky, dark, or otherwise abnormal color may indicate the presence of one or more contaminants. A milky appearance implies contamination by water. If the ﬂuid looks milky, take immediate action to avoid severe damage to your hydraulic system. Stop the inﬂux of water and remove the water from the system immediately. Water can be removed by passing the ﬂuid through water-absorbing ﬁlters, or by ﬂushing or draining the entire hydraulic system.
A marked change in the smell of the hydraulic ﬂuid can indicate a chemical breakdown. This type of breakdown is generally due to air that has become entrained in the ﬂuid, which creates varnish-like nitrogen-oil compounds that contaminate the ﬂuid. If a distinct change in the smell of hydraulic ﬂuid is detected, have it chemically analyzed by the manufacturer. Also consult with the system’s service engineer to determine if other changes or adjustments to the system are required.
Viscosity is a measure of the resistance of the ﬂuid to ﬂow. A low viscosity will not provide adequate lubrication to parts, resulting in increased wear on the parts. Many hydraulic ﬂuids will shear or thin out with use. A viscosity check should be made whenever ﬂuid samples are analyzed. If the ﬂuid’s viscosity is outside of the speciﬁed ﬂow limits, the ﬂuid should be replaced. (NOTE: Viscosity varies with temperature, so a numerical viscosity value is meaningless unless the temperature is speciﬁed.)
As hydraulic ﬂuid deteriorates over time, it oxidizes and produces deposits that may cause servo valves to stick. Signs of this natural process include changes in ﬂuid color, odor, or acidity level. Sludge, gum or varnish in the system are further evidence that oxidation has taken place.,
A ﬂuid analysis with an ultra-centrifuge test can detect the level of oxidization. The rate of oxidization increases signiﬁcantly at operating temperatures higher than 150° F (66° C). Oxidation is irreversible, and ﬂuid must be changed when oxidization is detected.
Water is highly undesirable in hydraulic systems. It can cause emulsions to form, and it can lead to corrosion. More than a trace of water may indicate an improper mechanical condition, poor performance of a heat exchanger or ingestion of water through the breather ﬁlter.
During system operation, gross contamination of hydraulic ﬂuid is indicated by a milky color. If the system is not in operation, contamination can usually be detected by sampling the ﬂuid at the bottom of the reservoir, where water normally settles as it separates from the hydraulic ﬂuid.
A simple test for water contamination is the “spat” test: Place a few drops of oil on a hot plate heated to above boiling, but less than 350° F; if the oil bubbles or sizzles, there is an unacceptable amount of water in the oil.
If water contamination exists, ﬁx the leakage and remove the water from the system immediately. Water can be removed by passing the ﬂuid through water-absorbing ﬁlters, or by ﬂushing or draining the entire hydraulic system.
These analyses are a valuable aid to troubleshooting. A high iron reading may indicate wear of hydraulic power unit parts. High silicon readings may indicate ingestion of dirt or compounds containing silicon (e.g., sealing compounds or defoamants). High copper readings may indicate component wear and/or faulty heat exchangers.
If ﬂuid analysis shows high levels of iron, silicon or copper, identify the source and replace components as necessary. Fluid analysis should be a continuing process and sample results must be evaluated for trends that indicate a change in the condition of the hydraulic system.
Regular monitoring and maintenance of the hydraulic ﬂuid will provide maximum operating performance and service life for the hydraulic system and its components. Keeping a maintenance log that records: Viscosity, Particle Count, Water, % by content, Total Acid Number, UC, Oxidation,
Filter changes, Fluid changes, Operating temperature-test results, pH test results, Other inspections or maintenance, This log will help to detect signs of deterioration and can be used to develop a schedule for changing ﬂuid.
Filters provide the ﬂuid cleanliness levels required by servo hydraulic systems. These sizes and efﬁciency ratings have proven to be effective in controlling the silt particles that cause erratic servo valve operation. Filters must be cleaned or replaced during routine maintenance of the hydraulic system.
Most ﬁlters supplied are not cleanable; refer to your manufacturer’s product information for guidance on changing ﬁlters. System ﬁlters must be capable of maintaining a normal ISO 4406 particle count of 16/13/9.
When a high particle count is identiﬁed the source of contamination should be located and corrected. Collecting samples from various system locations will help identify the source of contamination. Clean the hydraulic ﬂuid by changing the system’s ﬁlters and running the hydraulic power unit for a period of time. Filters will collect solid contaminants larger than a speciﬁed diameter After ﬁltering the hydraulic ﬂuid, check it for cleanliness. An ISO 4406 particle count reading of 16/13/9 or better is required for test systems. Some critical test applications may require an ISO 4406 level of 14/12/8. If the appropriate level can’t be achieved after cleaning, a change to the ﬁltration plan must be considered.
At installation, or after any of the system’s hydraulic components have been replaced, ﬂush the system to remove particle contamination. If the reservoir is very dirty, or if sludge or varnish is present, the system must be ﬂushed with a ﬂushing compound.
Flushing compounds are solvent free, oil soluble cleaners designed speciﬁcally for cleaning and ﬂushing gummy oxidation deposits and insoluble materials from hydraulic systems. Solvent ﬂushing is a costly, time-consuming process. Contact the system’s service engineer before using a ﬂushing compound.
The manufacturer should have designed, manufactured, shipped and installed your hydraulic distribution system to manage particulate contamination of the hydraulic ﬂuid. After the system is installed and ﬂushing operations are completed, the system should be trouble-free.
Precautions must always be taken to avoid contamination during installation or maintenance. When a plug, cap, hose or hydraulic component is removed, foreign matter can enter the system and eventually cause damage.
On complex systems with large ﬂuid capacities, and in distribution systems that use welded carbon steel pipe, contamination risk is high. A complete system ﬂush—before attaching actuators and servo valves—is imperative.
After the ﬂuid is cleaned or the system is ﬂushed, sample the ﬂuid for cleanliness. The proper cleanliness level is an ISO 4406 particle count of 16/13/9 or better. If necessary, clean the ﬂuid continuously until this level of cleanliness is achieved.
Any industry that uses fluid containing any ferrous magnetic or Para-magnetic particles will benefit from the installation of an Eclipse Magnetics Micromag, Filtramag or Automag magnetic filtration system.
Single stage filtration to Sub-Micronic Levels Standard’ media-based filtration would need two or three (or more) stages, with coarser prefiltration, to reach fine levels of filtration Increased oil/coolant quality/cleanliness = increased part quality/decreased wear etc.
Yes it does as there is:
Eclipse Magnetic Filters will not block or cause a restriction to flow in normal usage, even when fully saturated, no risk of oil/coolant starvation causing engines or gear boxes etc. to sieve, or tools to burn out etc Automated Self-Cleaning systems require no day-to-day maintenance or filter changes – ever! Manual Systems will not block, or cause a system shutdown by showing an increased differential pressure.
Magnetic filtration can be used in almost any environment where ferrous, para-magnetic and grinding medium contamination of a liquid is a problem.