PQ Index A Useful Warning System For Iron Content
A Particle Quantifier Index, or PQ Index, is an important predictive maintenance tool as it measures the total ferrous metal content in lubricants and is an indicator of abnormal metal wear, according to total fluid management provider Techenomics.
The presence of iron is detected by use of a magnetic field and the higher the PQ Index reading, the higher the total of ferrous material and this is generally associated with wear.
Techenomics utilises the PQ Index in its analysis and readings can also be taken by operators on site.
“It is important to make sure PQ measurements are taken from various engine compartments, such as gearboxes, differentials and final drives,” the company’s CEO Chris Adsett says.
“While the PQ Index does not take into account the size of ferrous particles, it measures the total amount of ferrous material present and if there are high amounts in one compartment, there is obviously an issue in that compartment, which is usually excessive wear.”
Techenomics Technology and Product Development manager Eka Karmila says it is much more accurate to rely on trends rather than one reading or established limits.
“Three measurements made at weekly intervals will identify what is a normal reading.
“For later measurements, any change in PQ Index greater than 10% will indicate that something is changing, and the sample should be sent to the laboratory for more expert assessment.
“Most models in the PQ range permit measurement of the sample directly in the sample bottle so the laboratory receives that actual sample for more detailed examination,” she says.
A Particle Quantifier exposes a lubricant to a magnetic field. Oil samples are subjected to a strong magnetic field which distorts when ferrous particles pass over. It can be used to measure ferrous wear metal particles in oil, grease and coolants.
Chris Adsett says a PQ reading can be particularly useful in components that are starting to fatigue or have large internal wear starting to appear.
Oil analysis accurately measures iron content where particle size is less than 10 µm but not above that size. This means both can be used to provide an accurate warning system.
“When PQ results and the iron level both indicate low readings, the sample will contain minimal iron particles most likely less than 10 µm and represent normal rubbing wear. When PQ results are low and iron is high, this most likely indicates particles are less than 10 µm and could be caused by acidic wear or larger amounts of rubbing wear.
“When both are high, there is most likely an abundance of smaller particles, however, when PQ is high and iron is low, this is a concern because the majority of wear is larger than 10 µm and will cause accelerated damage,” he adds.