WHY FILTER?

To clean the hydraulic oil,
To prevent the equipment from getting damaged due to contamination,
To reduce abrasion on the equipment,
To extend the service life of the equipment. 

Contamination in Hydraulic Oils and Lubricants

Contamination in hydraulic oils and lubricants are categorized in two groups: First degree and second degree contamination.

First Degree Contamination

Reasons for contamination resulting from the manufacturing process of the equipment:

• Welding slags
• Shavings
• Casting sand
• Paint debris

Reasons for contamination resulting from the installation process of the equipment:

• Broken and cut angles (burr formation)
• Free parts of press connections
• Debris of seals
• Debris of cleaning equipment
• Solid lubricant debris (filter clogging)
• Contamination occurred when refilling oil:
• Contamination caused by the production, mixing or refilling of the oil/lubricant.

First Degree Contamination

This kind of contamination occurs during and after commissioning. The reasons are as follows:

Deterioration caused by contacting surfaces of mechanical parts.

Caused by abrasion:

• Caused by material cleaning
• Mechanical damage to the equipment due to extremely high flow rates, which causes high pressure drops
• Particles in the oil
• Particles formed due to the cavitation resulting from sudden expansion of sections

Chemical abrasion and layering on the surfaces of the equipment

• Chemical change in the oil
• Extremely high water concentration
• Oil oxidation in polish form and debris-like resin

Dirt entering because of the dust around the machine and the particles in the air

• Damaged seals of hydraulic cylinders
• Damaged filter with insufficient capacity
• Leaking suction lines

Contamination due to mixing with foreign substances

• Water intake through condensation, damage to seals and the cooler
• Grease, anti-corrosion materials

Oil Cleanliness Codes

Cleanliness classes for hydraulic oils and lubricants are called oil cleanliness codes.  The most common classification for oil cleanliness codes is NAS 1638, which is used instead of the international ISO 4406 and SAE 4059.

Oil cleanliness codes according to ISO 4406

(Quotation from ISO 4406, published in 1999)

Classifying the cleanliness levels

According to ISO 4406, cleanliness codes can be measured with automatic and microscope particle counters.

Automatic Particle Counting

Cleanliness level classification for hydraulic oils is composed of 3 codes: > 4µm , > 6µm and > 14 µm

For example:

The oil sample taken from a hydraulic system was counted in an automatic machine.

Counting result is as follows.

Result: According to ISO 4406, hydraulic oil ISO 17/15/11

Result: According to ISO 4406 this hydraulic oil has an oil cleanliness of: ISO 17 / 15 / 11.

Particle Counting with Microscope:

As the conditions may require, some oil samples are counted with a light microscope. In this case, only 2 codes are used.

These codes are > 5µm and >15µm for all codes.

For example:

Oil cleanliness codes according to SAE AS 4059’ya

For fluids, NAS 1638 has been used up to date as an alternative to ISO 4406.

On the contrary to ISO 4406, this standard does not classify thin alluvion particles or > 70 µm particles.

Maximum number of particles in cleanliness classes for 100 ml oil