Oil Cleanliness

Cleanliness doesn't just refer to the particles that you can see - there are some that are  invisible to the naked eye.

Effects of Poor Oil Cleanliness

Poor quality oil can:

  • Damage interacting components via abrasion;.
  • Reduce component life via erosion;
  • Obstruct critical flow paths;
  • Damage servo or proportional valves;
  • Increase quality problems;
  • Increase customer dissatisfaction;
  • Reduce market perception;
  • Damage business opportunities;
  • Raise costs

What are the likely failures due to poor oil cleanliness?

Sudden or catastrophic - This is caused when a small number of particles invade a critical space and create a torque reaction large enough to cause a seizure or fracture which is irreversible.

Intermittent - Similar to that above but usually caused by smaller size structures. Intermittent events will eventually lead to sudden or catastrophic failures. Typical examples are temporarily blocked or unseated spool/poppet valves.

Degradation - Typically characterised by flow erosion, abrasion, polishing and general wear.

A Powerpoint presentation on Oil Contamination and Particle Counting  Powerpoint Icon

Lets make it crystal clear...

Cleanliness is a term used to describe the relative quantity of solid contaminant particles in any given system which is large enough to cause a seizure or fracture which is irreversible, e.g. piston pump. One can gauge a fluid's cleanliness by referring to a number of internationally-agreed standards. Every machine has an optimum cleanliness level. This level will be a balance between the maintenance of the machine's efficiency and the cost to maintain cleanliness.

Have a look at the comparison chart below

Oil Cleanliness Comparison Chart.

How is oil cleanliness measured?

If a gear system is filtered, particle count data may be useful. But if the gearbox is not filtered, particle count data doesn't provide as much information as would other tests such as PQ/FW (Particle Quantifier / Ferrous Wear) or DR (Direct Read) Ferrography. Diesel engine oil is black and requires different techniques to the tried and trusted laser counting methods. FW/PQ, DR Ferrography and Wear Debris Analysis are probably wiser choices. (WDA is a vital tool in failure and warranty issues).

The most common standard used to rate cleanliness is the ISO 4406. This table shows the ISO Codes that are used to represent the number of contaminant particles present in 1ml of oil

A table showing the ISO codes

ISO 4406
Number
Number of Particles per Millilitre
Greater than(>)
Less than(<)
24
80,000
160,000
23
40,000
80,000
22
20,000
40,000
21
10,000
20,000
20
5,000
10,000
19
2,500
5,000
18
1,300
2,500
17
640
1,300
16
320
640
15
160
320
14
80
160
13
40
80
12
20
40
11
10
20
10
5
10
9
2.5
5
8
1.3
2.5
7
0.64
1.3
6
0.32
0.64
5
0.16
0.32
4
0.08
0.16
3
0.04
0.08
2
0.02
0.04
1
0.01
0.02

The three-number code relates to the number of particles that are >4m, >6m and >14m in size. (1.0m* = 1.0 x 10-6m = 0.001mm) * The unit 'm' (micrometer) is commonly pronounced as simply "micron". So, an oil that gave readings of...

  • 72,064 particles >4m;
  • 16,519 particles >6m;
  • 541 particles >14m;

...would, after referring to the table, result in an ISO Code of 23/21/16.