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  • Anshuman Agrawal

Common mistakes of Oil Sampling and how to avoid them?


Routine Oil sampling and analysis are crucial for a successful maintenance program. It provides important information to determine the condition of the equipment. Sampling is a vital procedure for collecting fluid from machinery for the purpose of oil analysis. The results and reports of oil analysis depend on the quality of the oil sample. Thus, oil sampling must be performed keeping some important goals in mind -

  • To MAXIMIZE the Data Density.

  • To MAXIMIZE Consistency.

  • To MAXIMIZE Relevance.

  • To MINIMIZE Data Disturbance.


There can be three ways of extracting samples from a component - drain port, drop-tube (in a vacuum pump), and a dedicated sampling point. A common mistake is taking an oil sample from the reservoir in circulating and hydraulic systems. Taking samples from the tank is not a best practice. If the sample is taken from the drain lines before emptying the tank, the concentration of wear metal would be much higher. Let’s discuss the common mistakes of oil sampling which can be avoided -

  1. Some sampling methods are simply used for convenience, like inadequate flushing, using a vacuum pump (drop-tube sampling), usage of uncleaned bottles, etc. By following these bad practices, the quality of the sample taken is not apt and reliable.

  2. If the samples are collected from the bottom of the tank and sumps, they may show higher concentrations of the sediments and water.

  3. If the samples are consistently collected from the turbulent zones of reservoirs and tanks may not give reliable information.

  4. Sometimes the sample is collected consistently from downstream of pressure-line or off-line. In this case, sampling accuracy is not given importance.

  5. Samples collected from cold systems would not give correct information as the contaminants and other insoluble suspended particles would be settled when at rest.

  6. Dead zone fluids like standpipe, regenerative loops, etc. give wrong results as they possess different properties than that working fluids.


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The International Organization for Standardization (ISO) has some defined codes which are mostly used as the primary reviewed piece of data. Being consistent is important with sampling. It is not advisable to use different sampling methods.

Let’s discuss certain must-follow sampling rules for oil analysis -

  1. Collect samples from running machines not from cold machines or stand-by machines. It is always advisable to start the machine and take the sample and the time of sample should be when the machine is at its peak of stress.

  2. What, when, who, where, and how should be defined for oil sampling procedures as well, just like maintenance procedures are defined in detail. Changing the sampling methods or location is not advisable.

  3. Use a specific sample point based on the type of lubricant, pressure, and the fluid required.

  4. A sample must be taken in a bottle of the correct size and cleanliness. To get more information on bottle cleanliness, ISO 3722 can be referred to.

  5. Oil sampling is like examining the condition of the system for that point in time. It is advisable not to wait for more than 24 hours to send the samples for oil analysis. This is because the health of the system may change in a very short period. Early detection would help in early remedy.

  6. Maintain proper frequency of taking samples. Don’t do it whenever you feel like doing it. There should be an appropriate frequency so that important maintenance decisions could be taken on time.

  7. One of the major problems in oil sampling is cross-contamination. Don’t use dirty sampling equipment. Flushing is the solution to this which is often overlooked and the selection of suitable clear media is equally important.


Though every system has a unique consideration of sampling, the above-mentioned tips can be applied and taken care of for your sampling techniques/methods. Start applying it Today!!


Connect with Minimac Experts to strategize your Oil Analysis plan: enquiry@minimac.in or WhatsApp us at +91 70309 01267

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