Understand the particle count NAS standard

Current hydraulic systems are increasingly modern, efficient and productive. Manufacturers often act to reduce cycle times and clearances between metal surfaces, as they increase the machine’s pressure, power and digging force. These are major improvements, making current equipment more productive and easier to operate.

However, these improvements also brought a greater need for cleaning fluid systems during the product’s life, as they are more prone to premature wear and losses in efficiency. Contaminating agents in fluids can cause a significant decrease in productivity, through a slow and gradual process, in which such loss can go unnoticed in many cases.

In contaminated hydraulic systems, for example, there can be a loss of efficiency of up to 20% before the operator notices the problem, which would represent one day of wasted productivity per week, not to mention the possibility of catastrophic failures.

In order to combat this problem, some standards for particle control and counting were created, the main ones being ISO 4406, that we talked about earlier, and the NAS 1638 standard, the theme of our post today.

NAS 1638 and oil contamination classes

The NAS 1638 standard assesses the level of contamination by counting particles in 100 ml, according to five different size ranges, which can be seen below:

  • From 5 to 15 micrometers
  • From 15 to 25 micrometers
  • From 25 to 50 micrometers
  • From 50 to 100 micrometers
  • Greater than or equal to 100 micrometers

The classification of the NAS 1638 is simpler and more practical, occurring according to the size range most found among the five categories above in a given sample. The table below represents the different classes evaluated by this standard, ranging from number 00 to 12, where the first is the cleanest oil, and the last, the dirtiest oil, respectively. See below:

Micro
filtration
5 to 15
µm
15 to 25
µm
25 to 50
µm
50 to 100
µm
≥ 100
µm

C

L

A

S

S

E

NAS

00 125 22 4 1 0
0 250 44 8 2 0
1 500 89 16 3 1
2 1.000 178 32 6 1
3 2.000 356 63 11 2
4 4.000 712 126 22 4
5 8.000 1.425 253 45 8
6 16.000 2.850 506 90 16
7 32.000 5.700 1.012 180 32
8 64.000 11.400 2.025 360 64
9 128.000 22.800 4.050 720 128
10 256.000 45.600 8.100 1.440 256
11 512.000 91.200 16.200 2.880 512
12 1.024.000 182.400 32.400 5.760 1.024

Check the example below of a particle count in a fluid, by size ranges:

Size Amount NAS Class
5 to 15 µm 27.358 7
15 to 25 µm 239 3
25 to 50 µm 65 4
50 to 100 µm 10 3
≥ 100 µm 0 0

In the situation above, the analyzed fluid will be evaluated as Class 7, that is, the one found in greater quantity in the sample. This categorization works differently from the ISO 4406 standard, assigning only one class number. This aspect allows a quick and practical reading of the oil; however, it does not measure all the information related to the classification of the particles, nor their dimensions.

Conclusion

Constant monitoring of the cleanliness and quality of fluids is of paramount importance to ensure the good performance and productivity of your equipment. In this sense, methodologies such as filtering and microfiltration of hydraulic oil are fundamental, since they act in the elimination of contaminating agents.

This is a procedure that needs to be done even in new oil, since it may come with contaminating particles from the factory. In this way, you are prevented from a series of problems, requiring more interventions and higher costs, as in the case of pump or valve failures and premature equipment wear.

Do you want to know more about standards for particle counting, filtration, microfiltration and which one to use? Enter in contact with one of our experts or make aprice .

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