ISO 4406

The international standard ISO 4406, “Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles” provides a framework for reporting the concentration of contamination particles in hydraulic oil using an automatic particle counter (like the Hiac or Accusizer 780).  The older standard published in 1987 required particle concentration be reported at two sizes: 5 & 15 µm. This has been replaced in the new standard published in 1999 with three sizes; 4, 6 & 14 µm.

A three number scale is used to report the particle count – the first number represents the particles/ mL > 4 µm, the second number represents the particles/ mL > 6 µm, and the third number represents the particles/ mL > 14 µm. A scale number is assigned to a particle concentration range as shown in Table 1 below.

Number particles/mL

More than up to/including Scale number
2 500 000 28
1 300 000 2 500 000 28
640 000 1 300 000 27
320 000 640 000 26
160 000 320 000 25
80 000 160 000 24
40 000 80 000 23
20 000 40 000 22
10 000 20 000 21
5 000 10 000 20
2 500 5 000 19
1 300 2 500 18
640 1 300 17
320 640 16
160 320 15
80 160 14
40 80 13
20 40 12
10 20 11
5 10 10
2,5 5 9
1,3 2,5 8
0,64 1,3 7
0,32 0,64 6
0,16 0,32 5
0,08 0,16 4
0,04 0,08 3
0,02 0,04 2
0,01 0,02 1
0,00 0,01 0

 

The results should be presented as three numbers separated by slashes, such as 24/20/14. This result would refer to:

more than 80 000 and up to and including 160 000 particles equal to or larger than 4 μm

more than 5 000 and up to and including 10 000 particles equal to or larger than 6 μm

more than 80 and up to and including 160 particles equal to or larger than 14 μm