How to Perform Hydraulic Oil Analysis?
How to Perform Hydraulic Oil Analysis?
How to Perform Hydraulic Oil Analysis?
Where Should an Oil Sample Be Analyzed in a Hydraulic System?
To produce a representative sample, the oil must have a continuous flow through a marking pipe, preferably upward. Sampling points located around the bottom perimeter of a pipe tend to allow particles to accumulate in the sampling valve.
A sample taken between the pump and the filter housing of an off-line filter is normally the most contaminated part of the oil system. Therefore, this is where the total system contamination load is best represented.
If an off-line filter system is not installed, a vacuum type sampling pump is a valid option. In this case, the sample should be withdrawn 10 cm from the bottom of the tank.
To obtain an oil sample, the following is required:
200 ml particle-free glass bottle
five liter open oil container
a cloth
Please follow the instructions below before taking the oil sample.
Place the oil container under the sampling valve.
Open and close the valve five times and leave it open.
Flush the pipe by pouring it into a liter container.
Open the sample bottle, but avoid contamination getting inside.
Place the bottle under the oil flow without touching the sampling valve.
Fill the bottle approximately 80% full.
Place the cap on the bottle immediately after collecting the sample.
Shake the bottle, drain the oil from the container and repeat the filling.
Close the sampling valve.
All samples must be clearly identified with reference number, machine reference number, machine make and model, sampling location, date and oil type/brand.
Samples should only be collected with the machine operating at normal operating temperature.
Method is very important when sampling for particle counting.
Remember that you cannot make a better (cleaner) sample of the oil in the system, but it is possible to make a worse sample.
How Should I Evaluate Hydraulic Oil Analysis Data?
At least one oil analysis should include:
Solid Number of particles
Water Ratio in Oil (in ppm)
Oil Viscosity
Acid level in oil
If the oil additive content is notable, it should also be included in the analysis.
There should be a 0.8 micron Millipore membrane for sludge detection.
What is the Maximum Value Required for Hydraulic Oil?
Particle count: The first rule is that oil cleanliness should always be adjusted to the cleanliness requirements of the most sensitive component of the system. For example, if the hydraulic system uses servo valves, NAS class 6 or better is of great importance. In general, hydraulic systems should never exceed class NAS 7.
Water: Water content is expressed in PPM (parts per million). 1 PPM = 0.0001%. As a rule, the base water concentration should not exceed 300 PPM.
Viscosity: viscosity is expressed in cSt. Typical oil viscosity for hydraulic oil is 32 cSt, 46 cSt and 68 cSt mg/KOH g. Typical oil viscosity for lubricating oil is 220 cSt and 320 cSt. Fat viscosity can vary within a range of 25% or more of intimal viscosity. If the measured viscosity is between 33 and 59 cSt, a 46 cSt oil is still within an acceptable range.
Acidity level – Total Acid Number (TAN): Acidity level or TAN expressed in mg / KOH g. Every oil has a maximum TAN value. Ask your oil supplier about the maximum TAN level of the oil you need. Typically the maximum level for hydraulics is 1.0 mg/g KOH. New fresh oil will start around 0.2 mg/g KOH.
Particle Counting Standards in Hydraulic Oil:
ISO 4406 Standard:
To facilitate comparison of particle content, ISO 4406/2000 classification has been made for particle content.
Sudden deterioration in an oil system is caused by large particles in the oil (> 14 microns), while slower, progressive defects, such as wear and tear, are caused by smaller particles (4-6 microns).
This is one of the reasons why particle reference sizes are set at 4 microns, 6 microns and 14 microns in ISO 4406/2000.
A typical example contains each 100 ml of oil:
000 particles > 4 microns
000 particles > 6 microns
000 particles > 14 microns
This oil sample presented in the ISO classification table (right) has a contamination class of 19/17/14.
NAS 1638 standard:
NAS 1628 is an American standard that references contamination load based on fractionation of different particle sizes for 5 to 15 microns, 15 to 25 microns, 25 to 50 microns, 50 to 100 microns, >100 microns.
The difference is that NAS gives a detailed breakdown of different particle sizes larger than 5 microns.
Contamination Guide for Hydraulic Oils:
ISO 14/12/10 – NAS 4: Very clean oil, best for all oil systems.
ISO 16/14/11 – NAS 5: Clean oil is an absolute requirement for servo and high pressure hydraulics.
ISO 17/15/12 – NAS 6: Lightly contaminated oil, standard hydraulic and mineral oil systems.
ISO 19/17/14 – NAS 8: New oil for medium and low pressure systems.
ISO 22/20/17 – NAS 12: Heavily dirty oil is not suitable for oil systems
A cleanliness goal should be determined for each oil-filled system. This is the basic requirement to guarantee reliability at the lowest possible cost.
If a millipore membrane, a 0.8 micron cellulose membrane is used, it will show oil degradation.
What should be the Hydraulic Oil Analysis Frequency?
During the implementation phase of a condition monitoring system, analyzes should be carried out at least every six months to create a database of information.
Every oil system should have a log where analysis results are recorded.
The logbook should also contain information on oil type, oil change, separation, targeted ISO class code and oil analysis results.