Particle contamination is one of the most significant problems that lubrication technicians face when caring for hydraulic systems and oils. Without particle counting processes in place, you may be unaware of failure conditions or the accelerated wear and oil degradation happening inside your hydraulic equipment.
But by taking a proactive approach in caring for hydraulic fluids, we can decrease maintenance tasks, lower ownership costs, and reduce oil consumption over time as well.
What is oil particle counting?
Particle counting is considered by many to be the most critical test for used oil analysis. Particle counting measures and reports the size and scope of particles found in lubricating oil; it is especially helpful for hydraulic equipment. Whether you conduct an onsite particle count or send a sample to a commercial lab for testing, particle count data can provide valuable insights into the health of equipment and lubricants alike.
Particle count data is an important part of a proactive condition-monitoring program because it can indicate early-stage signs of abrasive wear that lead to failure. Particle counts also indicate whether your hydraulic fluid is clean enough to perform properly without causing damage to equipment. The overall cleanliness of your fluids can be ranked according to the International Organization for Standardization’s (ISO) cleanliness code chart.
Particle counting tests
There are three basic methods to determine the number of particles in a sample: optical microscopy, automatic optical particle counting, and pore blockage particle counting.
Optical microscopy takes a sample and examines it under an optical microscope, and the particles are manually counted. While time-consuming, this method is still considered the most reliable and accurate counting method.
Automatic optical particle counting
This method is one of the most widely used and relies on an instrument with either a white light source or a laser to count the particles. White light instruments pass particles through a detection zone where they create a shadow. This shadow is measured, giving an accurate read on the particle’s size. Laser counters count particles as they pass through and impede the laser beam, providing a precise read on the particle’s size.
Pore blockage particle counting
With this method, fluid passes through a mesh screen, and two instruments take different readings. The first instrument measures how the flow decreases as the membranes plug up the mesh screen. The other instrument measures the amount of pressure across the screen. Both instruments have their readings plugged into a software algorithm, where the particle count is calculated. Although this method isn’t as dynamic as the optical particle counter, it still provides great information on the concentration of particles in your oil.
Benefits of particle counting
Particle counting offers a plethora of benefits and uses for your hydraulic systems. First and foremost, it can identify a host of issues, including abrasive wear conditions, botched machine repairs, changes in atmospheric contaminations, and oil film failure problems. It can also verify the performance of different components, such as the seal exclusions, the centrifuge, the filter, and the pump. Particle counting can also help determine different metrics, such as the optimum filter change point and the new oil cleanliness level. All of these insights are invaluable when looking at machine health from a holistic viewpoint.
What a high particle count means for hydraulics
A high particle count can mean several things about the state of your fluids and hydraulic machines. Most importantly, it indicates that there is severe particle contamination taking place. Left unchecked, this could create a whole host of potentially expensive problems with your equipment.
Filtration can help to remove larger particles from oil and extend intervals between drain and fill procedures, but conventional filters can only do so much. To get rid of the smallest particles, the most common approach is to flush the system, drain it, and fill it with new, clean oil. This can cost you valuable time and may require a flushing service provider as well.
But it is possible to take a more proactive approach to cleanliness. Using oil regeneration technology, some plants maintain hydraulic oil in a highly clean state, removing even the nanoparticle contaminants that slip by conventional filters. This extends the life of the oil and ultimately has a significant impact on the life of the machine asset as well.
The bigger picture
Many of us know that particle contamination is a leading cause of failure, but what may surprise some is that smaller particles are of greater concern than larger ones. Particles that are similar in size to the lubricant’s film thickness cause the most damage to hydraulic systems because they get in between tight clearances and abrade component surfaces. Smaller particles can also lead to sudden and dangerous failure conditions when they get between the spool and bore of hydraulic valves in a phenomenon known as silt lock.
Still, not all machines are created equal. While you may not need to monitor particle counts on low-criticality or “run-to-failure” equipment, it’s important to set appropriate cleanliness targets on highly critical machines. While there are general guidelines for cleanliness, each machine is unique. Whether it is operating under different speed or load parameters or perhaps in a different operating environment, these factors influence how cleanliness targets should be set, especially for sensitive hydraulic equipment.
Cleanliness is key
Clean fluids are crucial for the proper maintenance of any machine, but hydraulic equipment truly does suffer most when contamination is present in oil. By monitoring a hydraulic fluid’s cleanliness, you can make adjustments along the way that keep equipment functioning properly. Whether you are looking for early warning signs of failure or ensuring that a hydraulic fluid is fit for service, particle counting offers highly valuable information about the state of your hydraulic fluid. Most onsite particle counting tools are relatively inexpensive, and even offsite testing is not cost prohibitive for most maintenance teams. If cleanliness targets are properly set and maintained, this “inexpensive” particle count data can help you significantly reduce maintenance tasks and lower the total cost of ownership for critical hydraulic assets.