Why Just One Oil Sampling Point Isn’t Always Enough

ISADRAULICS convey knowledge, experience and confidence to the consumer when we offer services such as auditing campaigns on your critical hydraulic rotating equipment with the primary goal to improve not only your oil cleanliness targets, but also improving your oil sampling techniques and practices. We partner with leading machinery and lubrication manufacturers, and engage in continual improvements in specialist training and education, for ‘best practice’ oil sampling practices and oil analysis understanding.


As part of this week’s TECHNEWS, we look into why just one oil sampling point isn’t always enough on critical hydraulic rotating systems for fixed plant.


Acknowledgment to: Author Wes Cash of Machinerylubrication.com


The starting point of any great oil analysis program begins with obtaining representative oil samples. The goal of oil sampling is to maximise data density while minimising data disturbance. You maximise data density by oil sampling in the right location with the right equipment at the right time.


Often, the right location is a “live zone” within the machine where oil is flowing in a turbulent manner. This allows you to capture an oil sample containing all the useful information needed for trending without losing any data via particle fly-by or settling.


The right equipment includes the use of minimess oil sampling valves, vacuum oil sampling pumps, disposable tubing and other accessories for taking oil samples as cleanly as possible. Depending on the criticality of the machine or how poorly it is operating, the oil sampling frequency may be very long (every six months) or very short (every two weeks).

Drawing consistent oil samples helps to trend wear debris, contamination levels and lubricant health.


Minimising data disturbance depends on how well the oil sample extraction process is designed. A common mistake is failing to flush the oil sample equipment as part of the procedure for drawing an oil sample.

If you are using disposable tubing and a vacuum oil sampling device, the tubing must be flushed to get a true representative oil sample. Flushing between five to 10 times the dead volume from all oil sampling equipment is recommended. This ensures that any contaminants inside the tubing are cleared out and that your oil sample will be representative of the conditions inside the machine.


Using the proper cleanliness specifications on the oil sample bottles will also help reduce the signal-to-noise ratio that can skew particle counting efforts. If you put oil into a dirty sample bottle, the results will show that the oil in the system is dirty when that isn’t necessarily true. Make certain that oil sample bottles are cleaned to the specifications required to hit your target cleanliness goals. If you receive oil sample bottles from a laboratory, call them and ask what quality-control process they have in place for the bottles and if they are certified to a specific cleanliness standard.

Choosing the correct oil sampling location can be challenging. When looking to install an oil sample port, target a single spot where you can gather as much useful data about the entire system. This is called the primary oil sampling location. At this location, the goal is to be able to draw a single oil sample that acts as a snapshot of the entire system. In most circulating systems, this will be on the main return line before the reservoir, or within the reservoir (before a pump) itself. By oil sampling from this one spot, you can check the wear debris from the rest of the system as well as the particle count to get an idea of the total contaminants in the system.


Although the primary oil sampling location is a great place to start, it often leaves behind a lot of valuable data. This is why secondary oil sampling locations should be installed on most systems. The goal of a secondary location is to be able to pinpoint the cause of any fault seen on an oil analysis report. Unlike the primary port, which provides an overall look at the entire machine, secondary ports enable you to focus on individual components inside the system.

Most circulating and hydraulic systems should have both a primary and secondary oil sampling location to ensure that any identified failure mechanism can be tracked back to the component causing the problem. Not only can a secondary port be used to help determine the source of wear debris or particles, but by installing oil sampling ports behind filters, you can monitor how well the filter is removing particles. So while the primary port may get the most use, the secondary port is invaluable once a fault has been detected.


Even though oil sampling can be a great predictive maintenance tool, a single sample port may not always be adequate for diagnosing abnormal conditions inside a machine.


To discuss your requirements for improvements to oil cleanliness in critical hydraulic rotating equipment and oil sampling best practices, please call ISADRAULICS on +61 7 4743 9139, or e-mail [email protected] for further information.

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