NAS 1638

NAS 1638 is an older standard developed in 1964 to define classes of contamination in aircraft components and hydraulic fluids. The classes refer to maximum number the particles in 100mL in different size classes. The table below shows the classification values that may still be in use for older specifications based on Hiac particle counters, but this standard officially became invalid in 2001. Most users use a single code number based on the highest particle count in any of the size bins.

code

5-15 µm

15-25 µm

25-50 µm

50-100 µm

over 100 µm

00

 125

22

 4

 1

 0

0

 250

 44

 8

 2

 0

1

500

89

16

3

1

2

 1000

 178

 32

 6

 1

3

 2000

 356

 63

 11

 2

4

 4000

 712

 126

 22

 4

5

 8000

 1425

 253

 45

 8

6

 16000

 2850

 506

 90

 16

7

 32000

 5700

 1012

 190

 32

8

 64000

 11400

 2025

 360

 64

9

 128000

22800

 4050

 720

 128

10

 256000

 45600

 8100

 1440

 256

11

 512000

 91200

 16200

2880

 512

12

 1024000

 182400

 32400

 5760

 1024