Hydraulic Oil Contamination and Cleanliness Standards

Oil contamination is the main cause of failure and malfunction in hydraulic systems and can also result in loss efficiency, excessive component wear.
However, using adequate cleanliness to guarantee reliability and extend all the system’s hydraulic components life.

ISO 4406
ISO 4406 defines the contamination level with 3 scale numbers that relate with the number of particles of average dimension equal or greater than 4 µm, 6µm, 14µm in 1ml of fluid.

NAS 1638
NAS 1638 is determined by counting the total particles of different size ranges contained in 100ml of fluid.

Cleanliness Recommendations:
Type of system
Type of valve
Recommended
Cleanliness Level
Recommended Level
for Extendec Product Life
ISO 4406
NAS 1638
ISO 4406
NAS 1638
  • Proportional valves
  • High pressure greater than 350 bar
  • Very high frequency cycle application
16/14/11
5
15/13/10
4
  • Operating pressure greater than 300 bar
  • High frequency cycle application
  • Poppet type (low leakage valve)
  • Electrohydraulic cartridge valves
18/16/13
7
16/14/11
5
  • Operating pressure less than 300 bar
  • Systems/Components with moderate dirt tolerance
19/17/14
8
17/15/12
6
  • Operating pressure less than 140 bar
  • Low duty cycle applications
  • Systems/Components with good dirt tolerance
21/19/16
10
19/17/14
6

※ Recommendations: If you are unsure the condition of oil contamination, please install high pressure filter (10 µm) at manifold (inlet) that can smoothly operate for most cartridge valves.


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