All About Air Compressor Oil Sampling: What, Why, How, and When

Aug 03, 2023

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Oil sampling is one of the most crucial aspects of industrial air compressor maintenance — and one of the most often overlooked. What is oil sampling, and why do you need to do it? Read on to learn all about air compressor oil sampling: what it is, why you should do it, how to sample your oil, and what you can learn from an oil sample.  

Why Do You Need to Conduct Air Compressor Oil Sampling?

Oil sampling is like a checkup for your air compressor. Just like your doctor might take blood to learn more about your physical health, an oil sample can tell you a lot about the overall health of your compressor. Taking an oil sample and sending it to a lab for analysis provides a snapshot of compressor performance at a moment in time. This can be useful for air compressor troubleshooting, predictive maintenance, and problem prevention. 

Why sample oil for your compressor? Air compressor oil is the lifeblood of your oil-flooded rotary screw or reciprocating compressor. Oil is necessary for lubricating moving parts of the air end, providing essential cooling properties, and sealing the compression chamber. The condition of the oil tells you a lot about how the compressor is performing. Is oil prematurely degraded? Is it contaminated by metal particles that indicate wear in the air end? Does it show signs of varnish? Is the viscosity off? Oil analysis provides important insights into compressor health and performance. For example, if the analysis shows a high level of metal particles, it may indicate that a component in the air end is wearing out and needs to be replaced. Or if the oil’s viscosity is found to be too high or low, it could signal that the oil isn’t suitable for the operating conditions and a different type of oil might be needed.

Benefits of Oil Sampling 

There are many benefits to conducting regular oil sampling for your industrial air compressor. 

  • Early Detection of Problems: Oil sampling can help detect potential problems before they cause a failure, allowing for preventive maintenance and repairs. This can save significant time and money.
  • Extend Equipment Lifespan: Regular oil sampling and subsequent maintenance actions can help extend the lifespan of your compressor, improving the return on your investment.
  • Reduce Unexpected Downtime: By detecting potential issues early, oil sampling can help minimize unexpected downtime, which can be very costly in terms of lost production.
  • Improve Efficiency: Oil sampling can help ensure your compressor is running efficiently. For example, if the oil is contaminated, it might cause the compressor to work harder, consuming more energy.
  • Monitor Oil Performance: Oil sampling can provide valuable information about the performance of your oil and when it needs to be changed. 
  • Establish Maintenance Trends: Regular oil sampling can help establish trends in wear and contamination over time, providing valuable data for improving maintenance practices and schedules.
  • Enhance Safety: By helping to prevent equipment failures, oil sampling can also contribute to a safer working environment.

What Can You Learn About Your Compressor from Oil Sampling and Analysis?

Oil sampling and analysis can provide a wealth of information about the condition of your compressor. Here are some key insights that it can offer. 

  • Wear Metals: The presence of certain types of metals in the oil can indicate wear on specific parts of the compressor. For example, high levels of iron might suggest wear on steel components, while aluminum could indicate wear on aluminum parts.
  • Contamination: The presence of contaminants, such as dust, dirt, or water, can indicate problems with the compressor’s filtration system or seals. High levels of contamination can cause wear and damage to the compressor.
  • Oil Degradation: Over time, the oil’s physical and chemical properties can change due to heat, pressure, and other factors. By analyzing the oil, you can detect signs of oxidation, acid formation, and other indicators of oil degradation.
  • Additive Depletion: Most compressor oils contain additives that enhance their performance. Oil analysis can detect the levels of these additives and indicate when they are depleted, which can affect the oil’s ability to protect the compressor.
  • Viscosity Changes: The viscosity, or thickness, of the oil, can change due to factors like temperature and contamination. Changes in viscosity can affect the oil’s ability to lubricate the compressor effectively.
  • Particle Count: Oil analysis can provide a count of the particles in the oil, which can be an indication of wear or contamination.

By regularly analyzing these and other factors, you can gain a deep understanding of your compressor’s health and make informed decisions about maintenance and repairs. However, it’s important to interpret the results in the context of the specific compressor and its operating conditions. Factors such as the compressor’s age, usage patterns, and maintenance history can all affect what constitutes “normal” or “abnormal” results for that particular machine.

Types of Oil Analysis 

When you send an oil sample from your air compressor to a lab, they can perform several types of analysis to assess the condition of the oil and your equipment. Here are some common types of oil analysis.

  • Spectrometric Analysis: This test identifies and measures the amount of various metal particles in the oil, which can indicate wear on specific components of the compressor.
  • Particle Count: This test determines the number of particles of various sizes in the oil. A high particle count can indicate contamination or abnormal wear.
  • Viscosity Testing: This measures the oil’s resistance to flow, or thickness, at specific temperatures. Changes in viscosity can affect the oil’s ability to lubricate the compressor effectively.
  • Acid Number (AN) or Base Number (BN) Tests: These tests measure the oil’s acidity or alkalinity, respectively. A high acid number can indicate oil oxidation or contamination, while a low base number can suggest additive depletion.
  • Water Content: This test measures the amount of water in the oil, as water can cause corrosion and other problems.
  • Infrared (IR) Spectroscopy: This test can identify certain types of contamination and degradation in the oil, such as soot, water, coolant, fuel, and additives.
  • Fourier Transform Infrared (FTIR) Spectroscopy: Similar to IR spectroscopy, FTIR can identify and quantify certain chemical contaminants and degradation products in the oil.
  • Flash Point Testing: This measures the temperature at which the oil gives off vapors that can ignite. A lower-than-normal flash point can indicate contamination.
  • Ferrous Density: This test measures the amount of ferrous (iron-based) particles in the oil, which can indicate steel component wear.

These tests can provide a wealth of information about the condition of your compressor and the oil, helping you make informed decisions about maintenance and repairs.

How to Take an Oil Sample from an Air Compressor

It’s fairly simple to take an oil sample from your industrial rotary screw or reciprocating air compressor. You can have this done by a service professional, or you can do it yourself. Here are the steps for taking an oil sample from an air compressor: 

1. Safety First: Always ensure that you’re wearing the appropriate safety gear (gloves, goggles, etc.) before you begin. 

2. Choose the Right Oil Sampling Kit: Before you take an oil sample, you’ll need to have an oil sampling kit. These kits typically include a sample bottle, tubing, and other necessary tools. The sample bottle should be clean and dry to prevent contamination. Check with your compressed air service partner to get an oil sampling kit. 

3. Locate the Sampling Point: The sample point is typically a valve or port located somewhere along the oil system. This is where you’ll extract the oil from. The sampling point should be in an active oil flow area for the most representative sample. Check your air compressor user’s manual to locate the sampling port for your specific make and model. 

Closeup of oil sampling port on an industrial air compressor

4. Prepare the Sampling Point: Before taking the sample, clean the area around the sampling point to avoid any dirt or contaminants entering the sample. This might involve wiping it with a clean cloth or using compressed air to blow away any dust or debris.

5. Take the Sample: Once the area is clean, you can start collecting the oil. The specific method will depend on your sampling kit. Usually, you’ll connect the sampling tube to the sample point and then into your sample bottle. The sample is usually taken while the compressor is running under normal load conditions. Be careful not to overfill the bottle – you typically only need a few ounces.

Closeup showing tubing going into the oil sampling port of an industrial air compressor to take a sample

6. Seal and Label the Sample: After taking the sample, securely seal the bottle and label it. The label should include information like the date, the machine from which the sample was taken, the oil type, and any other relevant details.

7. Send the Sample for Analysis: Finally, send the sample to a laboratory for analysis. They will check the oil for signs of contamination, wear particles, and other indicators of the health of your air compressor.

Closeup of a compressor oil sampling bottle showing someone filling the bottle with dark oil from a sampling tube

How Often Should Oil Sampling Be Completed for Industrial Air Compressors?

The frequency of oil sampling for an industrial air compressor can depend on a variety of factors, including the type and age of the compressor, its operational conditions, and the criticality of the compressor to your operations. However, a common recommendation is to perform oil sampling at least every 6 months or 2,000 operating hours for preventative maintenance purposes. 

If your compressor is new, you might want to sample the oil more frequently at first to establish a baseline and understand how the machine is wearing in. If your compressor is running in harsh conditions or operating continuously, more frequent oil sampling (like every 3 months) might be necessary. Additionally, if the compressor is critical to your operations – for instance if a failure would lead to a significant production loss – more frequent sampling can help catch problems early and avoid costly downtime. Frequent sampling may also be recommended as your compressor ages to keep an eye on emerging issues and predict the remaining life of your compressor. 

But remember, these are general guidelines. It’s always a good idea to consult with your compressor manufacturer or a maintenance professional for advice tailored to your specific situation.Compressor oil sampling bottle, filled with dark oil, and used sampling tubing

Is Oil Sampling Required for an Air Compressor? 

While skipping oil analysis may not have a direct impact on compressor operation, regular oil sampling may be required to maintain your air compressor warranty. That’s because air compressor manufacturers and service providers know that oil sampling acts as an early warning signal for emerging compressor problems. Paying attention to the results of your oil analysis, and fixing issues with your compressor while they are in the early stages, will significantly increase the life of your air compressor and prevent more expensive problems down the road. 

For our Extend Aire Warranty Program, we require oil sampling every 6 months or 2,000 hours of operation.

Get Your Oil Sample Started Today!

Time for your next oil sample? Contact Fluid-Aire Dynamics for a free oil sampling kit. We’ll help you get started so you can extend the life of your air compressor and detect emerging problems before they cause unnecessary downtime or compressor damage. 

Fluid-Aire Dynamics is your air compressor service partner. Contact us for preventative maintenance, diagnostics, repair, or compressed air system optimization. 

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