The time factor when taking samples correctly

Can the validity of an oil sample change because the wear particles suspended in the oil deposit too quickly? One of our industrial gearboxes is regularly monitored using your lubricant analyses. The last analysis suddenly showed an exceptionally low PQ value. All other values were on trend. A control sample taken a few days later showed the expected PQ index. As always, we did not take the anomalous sample from or just in front of the oil sump after a long weekend. However, the gearbox was not in operation, otherwise we have always taken the sample during operation. Could this have influenced the result?



Sedimentation speeds and duration

Steel particle size

Sedimentation speed

Sedimentation duration
for 0.5m distance

at 0°C in oil ISO VG 320

5 µm

0.000018 mm/s

322 days

50 µm

0.003 mm/s

2 days

500 µm

0.282 mm/s

30 minutes

at 20°C in oil ISO VG 320

5 µm

0.000073 mm/s

79 days

50 µm

0.011 mm/s

12.5 hours

500 µm

1.14 mm/s

7 minutes

at 60°C in oil ISO VG 320

5 µm

0.00052 mm/s

11 days

50 µm

0.082 mm/s

1.5 hours

500 µm

8.16 mm/s

1 minutes


OELCHECKER Winter 2014, page 8