Most hydraulic failures don’t start with a broken part. They start with particles too small to see. Fine dirt, wear metal, and other debris circulating in the fluid gradually wear down pumps, valves, and actuators until something gives out. Measuring how clean that fluid actually is lets you catch the problem before it becomes downtime.
That’s why we’ve expanded our services to include hydraulic fluid cleanliness testing, built around two instruments: the PAMAS SBSS automatic particle counter and the JOMESA HFD automated microscope system.
Why Particle Technology Labs?
Particle characterization is what we do. Since 1992, Particle Technology Labs (PTL) has helped pharmaceutical, industrial, and research clients measure and understand particles of every kind. Hydraulic fluid cleanliness is a natural extension of that work. Our team brings the same expertise in particle counting, particle sizing, and microscopy to the fluids that keep equipment running.
How the PAMAS SBSS Works
The PAMAS SBSS (Syringe Bottle Sampling System) is an automatic particle counter built for laboratory fluid analysis. As the sample passes through a light-extinction sensor, the system counts and sizes each particle individually. The system degasses the sample under vacuum and automatically controls pressure and sample volume, keeping results consistent from run to run. It handles a wide range of oils, including hydraulic, turbine, insulating, and gear oils, as well as viscous fluids up to 1600 cSt.
Our testing follows the procedures outlined in ISO 11500, using a particle counter calibrated to ISO 11171. That calibration is what the “(c)” in a size like 4 µm(c) refers to. Because every particle is measured individually, automatic counting produces a true size distribution, which pore-blockage methods cannot provide because they estimate contamination based on how quickly a mesh clogs.
What You Get Back
Every PAMAS SBSS report includes cleanliness codes in two widely used formats, ISO 4406 and SAE AS4059, along with the underlying particle counts by size.
An ISO 4406 code is written as three numbers, such as 18/16/13, representing particles at ≥4, ≥6, and ≥14 µm(c). Lower numbers mean cleaner fluid, and each step up roughly doubles the particle count. SAE AS4059 expresses cleanliness as a class based on particle counts across a wider range of sizes, and is often referenced in aerospace and defense specifications. Most equipment manufacturers publish target cleanliness levels for their systems, so you can compare your results directly against those targets.
See a sample report: https://particletechlabs.com/wp-content/uploads/2026/09/PAMAS-Analysis.pdf
When Microscopic Analysis is the Better Choice
Automatic counting works well for most clear fluids, but some samples can throw it off. Water droplets and air bubbles can be counted as particles, and very dark or heavily contaminated fluids can overwhelm the optical sensor.
For these samples, we use our JOMESA HFD, an automated optical microscope system, following the procedures outlined in ISO 4407. The sample is filtered onto a membrane, and the HFD scans it to count and size the particles, sort them into metallic and nonmetallic, and capture images of the largest ones. That gives you a visual picture of the contamination in your fluid. As a general guide, metallic particles can indicate wear inside the system, while nonmetallic particles and fibers often come from outside it. Microscopic counts are reported at ≥5 µm and ≥15 µm.
Example particle images from a JOMESA HFD report, showing the largest metallic and nonmetallic particles found on the membrane.
See a sample printout: https://particletechlabs.com/wp-content/uploads/2026/10/Jomesa-Test-Dust-1.pdf
Which Test Do I Need?
| Your Sample | Recommended Test |
|---|---|
| Clear hydraulic, gear, turbine, or insulating oil | PAMAS SBSS automatic particle count, with ISO 4406 and SAE AS4059 codes |
| Visible water, haze, or air bubbles | JOMESA HFD microscopic analysis, following the procedures outlined in ISO 4407, with counts reported at ≥5 µm and ≥15 µm |
| Very dark, opaque, or heavily contaminated fluid | JOMESA HFD microscopic analysis |
| You want to see the particles, not just count them | JOMESA HFD, which captures images and sorts particles as metallic or nonmetallic |
| Not sure | Contact us, and we will recommend the right method |
Who We Work With
Cleanliness testing matters anywhere hydraulic or lubrication systems are critical to performance. That includes automotive, aviation, and transportation; industrial machinery and components; chemicals and petrochemicals; power generation; and heavy-equipment manufacturers and their suppliers who need to verify fluid cleanliness against equipment manufacturer specifications. We also support fluid and filter manufacturers looking to confirm the cleanliness of their own products.
Coming soon: PTL will soon add this fluid cleanliness testing to our ISO/IEC 17025 accreditation scope. Sign up to receive news the moment this goes live!
Get Started
To request hydraulic fluid cleanliness testing, or to talk through which method fits your samples, how to collect and send them, and turnaround times, contact us at sales@particletechlabs.com or visit https://particletechlabs.com/contact/.
By Jorie Kassel, Laboratory Division Manager
