Compressor Vibration Analysis: How Technicians Diagnose Air Compressor Vibration

Rotary screw compressors are rotating machines. So, you can expect some vibration. But how much is too much? It depends.

The reason? Each compressor is different.

We manufacture our compressors following exacting standards, of course. But after you install a compressor, it’s a whole different ballgame. Two compressors could be identical when they leave our plant. Then they are plunged into the real world. Altitudes are different. Ambient temperatures are different. Humidity, power sources and uses are different. All those factors affect how an individual compressor performs in a specific setting.

That’s why compressor vibration analysis matters. It turns a vague sense that a machine “sounds rough” into data you can act on. It tells you whether the vibration is normal for your machine, what is likely causing it and how quickly you need to respond.

Vibration is an important indicator of your compressor’s overall health. The key is knowing how to measure it and what the readings mean. That’s what this guide covers.

What Is Air Compressor Vibration Analysis?

Air compressor vibration analysis is the process of measuring a compressor’s vibration, breaking that signal into its individual frequencies and comparing the results to a baseline. Because each mechanical fault vibrates at a characteristic frequency, the analysis shows not only that something is wrong but what is wrong.

Every compressor has its own vibration signature. As it runs, the airend bearings, the rotors, the motor and the belts or coupling each produce vibration at a predictable frequency. A technician captures that signature with an accelerometer. It is a small sensor, usually mounted with a magnet.

Software then converts the raw signal using a mathematical process called a fast Fourier transform. The result is a spectrum: a chart of vibration strength at each frequency. Peaks in the spectrum point to specific components.

Trend those peaks over months and you can see a bearing begin to fail long before it gets loud enough to hear. Trade publication Plant Engineering describes vibration analysis as a predictive way to track a machine’s health and diagnose current or future faults.

Vibration Analysis vs. Vibration Monitoring vs. Shock Pulse

These three terms get used interchangeably. They are not the same thing.

• Vibration monitoring tracks the overall vibration level over time. It tells you when vibration is rising.
• Vibration analysis breaks the signal into frequencies to identify the cause. It tells you why vibration is rising.
• Shock pulse measurement detects the tiny impacts produced inside rolling-element bearings. It is a focused check on bearing condition and lubrication.

Most maintenance programs use monitoring to flag a change and analysis to diagnose it.

Vibration Itself Is Not a Primary Indicator

Excessive vibration can cause several different problems for your compressor and your compressed air system:

• Downtime. Vibration can indicate that something is seriously wrong and that failure is imminent. A breakdown can take production offline.
• Electricity cost. Too much vibration probably indicates a problem serious enough to increase your machine’s power consumption.
• Equipment life. Vibration increases wear on seals, bearings and couplings and can shorten a compressor’s expected lifespan.
• Sound. Vibration makes a piece of equipment that’s sometimes noisy even louder.
• Loosening. Prolonged vibration may loosen bolts, mounting brackets and other fasteners. Pipe fittings, seals and welds may begin to leak.

The stakes can be high. How high? It all depends on what’s causing the vibration.

What Causes Compressor Vibration?

Several different factors can cause compressor vibrations. Some are mechanical faults inside the machine. Others are installation or site problems that have nothing to do with the compressor itself.

• Bearings. Vibration may indicate the bearings are showing signs of increased wear. It’s the cause most operators suspect first.
• Alignment. Long-term wear can cause the rotors of rotary screw air compressors to become misaligned. In direct-drive machines, the coupling between the motor and airend can also drift out of alignment.
• Unbalance. A rotating part with uneven weight, such as a damaged cooling fan or a motor rotor that has lost its balance, vibrates once per revolution.
• Mounting bolts and shipping brackets. Check that all major bolts and brackets are tight. The problem also may have started during installation, with workers failing to remove the bolts and brackets used to hold the machine in place during shipping. Those often cause unusual noises and vibrations when left in place.
• Enclosures. All Kaishan compressors come with heavy-duty, sound-deadening enclosures using thicker gauges of steel or aluminum. Even so, a loose panel or missing fastener on any enclosure can rattle and add vibration of its own.
• Belts. Belt-drive machines can vibrate from worn belts, poor tension and misaligned pulleys. To prevent that, we have equipped KRSB belt-drive rotary screw air compressors with automatic belt tensioning to provide longer belt life and ideal tension with no belt slippage.
• Piping strain. Rigid piping that is forced into position can pull on the compressor and transmit vibration in both directions.
• Electrical problems. Motor issues such as an uneven air gap or loose windings create vibration tied to the power supply rather than shaft speed.
• Location and base. An uneven or flexible floor lets the machine rock. Your compressor should rest on a flat, solid surface.
• Other equipment. Vibration could originate from other machines nearby and transfer to your compressor. Presses, stamping lines and large fans in automotive and general manufacturing plants are common sources.

Reading Compressor Vibrations: Common Fault Signatures

Here is where compressor vibration analysis earns its keep. Each fault leaves a fingerprint at a specific frequency, usually expressed as a multiple of running speed. “1x” means once per shaft revolution. “2x” means twice per revolution, and so on.

How Much Compressor Vibration Is Too Much?

It depends. That’s not a dodge. It’s how the standards are written.

The most widely cited vibration standard for industrial machinery is ISO 20816-3. It covers machines rated above 15 kilowatts. But its scope specifically excludes rotary positive displacement compressors, including screw compressors.

Screw compressors are addressed instead by VDI 3836, a German guideline that supplements the older ISO 10816-3. It sets housing vibration limits for four groups of screw compressors and Roots blowers, measured at the bearings while the machine runs on site.

For most facilities, the more useful benchmark is your own machine:

• Compare to your baseline. A reading well above your startup baseline deserves attention, even if it still falls inside a published limit.
• Watch the trend. A slow, steady rise usually signals wear. A sudden jump points to something that changed, such as a loose bolt or a failed part.
• Match the operating conditions. Vibration changes with load, pressure and temperature. Compare readings taken under similar conditions.
• Ask your manufacturer. If you contact us about vibration, the first thing we will ask for is your baseline measurement.

Vibration Alone Is Not a Diagnosis

Many operators immediately jump to the conclusion that their bearings are failing. They may be right. Grinding noises would be further confirmation.

But vibration itself is not a sole indicator. It’s like a runny nose. It could be a symptom of many things. You could easily misdiagnose a problem if you’re only focusing on vibration. There’s usually not enough information to identify the root cause.

How to Perform Compressor Vibration Analysis

You don’t need to be a certified analyst to start. You do need to be consistent. Follow these steps:

1. Capture a baseline at startup. The best time is when your machine is running properly. Take a reading immediately after initial startup. Every future reading is compared to this one.
2. Mark your measurement points. Measure the motor and the airend at each bearing. Take readings in three directions: horizontal, vertical and axial. Mark the spots so every reading lands in the same place.
3. Record operating conditions. Note the load, discharge pressure and temperature with each reading. Vibration that looks high at full load may be normal for that condition.
4. Trend the results. Plot each reading against your baseline. A rising line tells you more than any single number.
5. Gather other indicators. Check oil and temperature before you act. Metal particles in the oil may mean your bearings are starting to go bad. We recommend collecting an oil sample and having it analyzed every 2,000 hours. Significant temperature changes could also indicate more serious problems.
6. Correct the simple causes first. Tighten all bolts and mounting brackets. Check that the compressor rests on a flat, solid surface. Do not bolt down a rotary screw compressor.

Proper lubrication also protects the bearings that vibration analysis watches most closely.

Compressor Vibration Monitoring: Route-Based vs. Continuous

Once you have a baseline, you need a plan for keeping watch. There are two main approaches to compressor vibration monitoring.

Route-Based Monitoring

A technician carries a handheld vibration meter on a regular route and takes readings at the same points each visit. Plant Engineering recommends collecting a vibration profile at quarterly preventive maintenance visits and at least once a year. This is the most common approach for single compressors and smaller systems.

Continuous Monitoring

Permanently mounted sensors stream vibration data around the clock. Software flags readings that cross a threshold and alerts your team. It’s part of the broader Industrial Internet of Things.

Continuous monitoring makes the most sense for baseload compressors, critical processes and plants that run 24/7. In those settings, an unplanned shutdown costs more than the sensors.

Route-Based vs. Continuous at a Glance

Add Vibration to Your Maintenance Checklist

Whichever approach you choose, make vibration part of routine maintenance. You’re already measuring voltage, amps and temperature. Add a vibration reading to the same visit.

Many technicians also carry a shock pulse monitoring meter to check bearing condition. An SPM test is an essential tool for air compressor troubleshooting.

The addition of the baseline reading to your routine maintenance underscores the importance of having a maintenance program in the first place. You can avoid many problems that cause vibration with a good maintenance program. It will also help extend air compressor lifespan.

For more guidance, read our blog post “What You Need to Know About Rotary Screw Compressor Maintenance.” Or download our white paper, “Air Compressor Maintenance: Ultimate Guide and Checklist.” The U.S. Department of Energy’s compressed air sourcebook is another good reference for building a broader program.

Still Having Vibration Issues? Get Local Help

If you’re seeing an increase in compressor vibration after taking these steps, call in an experienced compressed air professional. They can take your vibration analysis to the next level. And they can prevent the downtime, damage and higher electricity cost that may result from the underlying issue.

We partner with independent, local distributors because it’s the best way to serve you. Your Kaishan distributor, who is independently owned and operated, can diagnose vibration problems on site and lead you to solutions. With factory-trained technicians and a deep understanding of industrial applications, they help maximize efficiency and minimize downtime. They also provide ongoing maintenance, service and parts.

Choosing a provider? Start with our list of ten questions to ask a prospective compressed air service provider.

Frequently Asked Questions

Key Takeaways

• Rotary screw air compressors are rotating machines, so you can expect some vibration.
• Compressor vibration analysis breaks vibration into frequencies to identify which component is causing it.
• Vibration can lead to downtime, higher electricity cost, shorter equipment life, noise and loosened fasteners.
• Bearings, alignment, unbalance, mounting hardware, belts, piping, electrical issues and nearby equipment can all cause vibration.
• ISO 20816-3 excludes screw compressors. VDI 3836 covers them, but your own baseline is the most useful benchmark.
• Vibration alone is not a diagnosis. Confirm with oil sampling and temperature readings.
• Use route-based monitoring for most units and continuous monitoring for critical or baseload compressors.
• If the problem persists, get help from a qualified compressed air professional.

Let Us Help

Vibration in your rotary screw air compressor may be an indication of more serious problems. Resolving those issues quickly protects your compressed air system and every process that relies on it. If you need help getting to the root causes of air compressor vibration, get in touch with the experts at Kaishan. Contact us today.