I was excited to see your December article Additives Confound the Count by Martini and Deskin. It is always nice to see controlled experiments confirm what we have long believed: Optical particle count results are raised by the presence of additives, and filtration strips out these useful compounds along with other particles.

Polaris Laboratories has recently switched from using ISO 11500 with traditional optical scanners to ASTM D7647, the dilution method recommended at the end of the article. We found the results to be as the article suggested-dissolving the soft particles and additives allows us to accurately measure the hard particles that pose the greatest risk to the system.

However, we have found a way to reduce the high cost of performing ASTM D7647 by using a CINRG Automatic Laboratory Particle Counter, which was designed with the dilution technique of ASTM D7647 in mind. The system quickly prepares and scans samples so we can offer a more valuable method of fluid cleanliness testing to the marketplace at a price similar to conventional optical scanners.

Using ASTM D7647 provides a better representation of the hard particles that accumulate in the fluid system, but some of the soft particles it avoids counting can also harm equipment. Soft particles formed from fluid degradation and water contamination may not be included in this ISO code result, yet they do pose a risk. This is why we recommend that particle counting be included with a suite of testing in order to evaluate overall fluid system health and reliability.

Determining the cleanliness of new lubricants also poses a problem. Testing a sample from a bulk tank is sufficient to baseline most fluid characteristics, but particle count is the exception. Fluid systems typically contain a filter, or the fluids are run through a filter cart before being added to a system. Either way, this changes the particle count compared to a bulk tank sample. In addition to these methods, Polaris Laboratories evaluates fluid cleanliness based on the system requirements. This means the particle counts in fresh lubricant are less important (unless they are used to confirm the ISO code of a specially requested fluid or to track down contamination sources).

Overall, adopting ASTM D7647 allows us to provide more specific maintenance recommendations by eliminating non-hard particles from particle count results.

Thank you for presenting quality articles that demonstrate the finer points of fluid analysis and the products that keep our equipment operational.

David Swanson

Polaris Laboratories

Indianapolis