Every rotating machine vibrates. Engines, compressors, pumps, generators, they all produce forces and vibrations that travel through into frames, structures and any external or connecting components. Some of that vibration is harmless. Some of it isn't. The problem is that you can't tell the difference by simply looking at your machine.
That's what vibration analysis is for. Whether this be the frequencies, the amplitudes or the direction of movement, vibration analysis measures what's actually happening and turns it into data that engineers can work with. And whilst this analysis has plenty of uses in predictive maintenance and condition monitoring, it should not be treated in isolation. The key to a successful analysis is implementation, and this ties into selecting the right anti-vibration mounts.
At AV Industrial Products, vibration analysis is a core part of how we specify mounts. It's the difference between choosing a mount based on load and assumption alone and choosing one based on factual, insightful data.
How Does Vibration Testing Prevent Excessive Vibration?
When selecting anti-vibration mounts, there is often one common oversimplification. An engineer looks up the weight of a machine, divides it across four mounting points, and picks a mount rated for that load. Structurally, it holds the machine up and the job is perceived to be done.
Except it isn't. The machine still vibrates excessively. This increases the wear and stress on the mounts, potentially reducing their lifespan to a matter of months rather than years. In some cases, the vibration at the mounting points is actually worse than it would be with no mounts at all.
Anti-vibration mounts don't just carry load, they're dynamic components with their own stiffness, damping and natural frequency characteristics. If those characteristics don't match the vibration profile of the machine, performance suffers. If the selection is wrong, you could end up in resonance, where the mounting system amplifies vibration instead of reducing it.
Vibration analysis is a preventative measure by telling you what frequencies the machine produces, how much energy is in each one, and what the mount needs to do to isolate them effectively.
What Vibration Analysis Actually Measures
At its simplest, vibration analysis involves attaching accelerometers to the machine, or the structure, and recording what happens during operation. Modern sensors measure movement in three axes: vertical, horizontal and longitudinal, and captures data across a wide frequency range.
The raw output is a time-domain waveform: a graph of acceleration against time. It tells you something is happening, but not a great deal about what. To understand the waveform and convert it into digestible, actionable information, we conduct a FFT analysis.
What is FFT Analysis: Breaking Vibration Down by Frequency
Fast Fourier Transform (FFT) is the standard method for converting time-domain vibration data into the frequency domain. Instead of showing you movement over time, it shows you which individual frequencies are present in the signal and how much energy each one carries.
This matters enormously for mount selection, because anti-vibration mounts don't distribute all frequencies equally. Their isolation performance depends entirely on the relationship between the excitation frequencies and the natural frequency of the mount system.
For example, if we take a diesel engine running at 1,500 RPM. The excitation frequency is 25 Hz (1,500 ÷ 60). But FFT analysis will typically reveal the data at all different Hz, creating a full picture. It will also capture other data showing firing frequencies, auxiliary drive frequencies and resonances that wouldn't be obvious from the running speed alone.
All of these frequencies need to be considered when selecting a mount. An isolation system that handles 25 Hz well but sits right on top of a 50 Hz harmonic will still exert significant vibration.
How Vibration Analysis Supports AV Mount Selection
Once you have a clear picture of the excitation frequencies outlined during your vibration analysis, mount selection becomes a much more data-driven, rational process.
The fundamental principle is that a mount's natural frequency must be substantially lower than the lowest significant excitation frequency. The wider the gap, the better the isolation.
As a rough guide, the excitation frequency needs to be at least 2.0 times the mount's natural frequency before useful isolation begins. At this ratio, you're typically achieving 85–90% isolation.
Vibration data lets engineers work through this properly rather than guessing. It allows them to:
Set the target natural frequency:If FFT shows the lowest dominant excitation at 25 Hz, the mount system needs a natural frequency well below that to deliver meaningful isolation.
Evaluate stiffness requirements: Knowing the target natural frequency and the mass, you can calculate the stiffness the mount needs to provide. This directly narrows down the product options.
Avoid resonance: This is the most important factor that is assessed during vibration analysis. Without vibration data, there's no reliable way to confirm that a mount won't resonate with the machine. Vibration analysis identifies the danger zones so they can be accounted for when selecting the appropriate anti-vibration mount.
Account for multiple excitation frequencies: Real machines don't just produce a single frequency. They produce a spectrum across a range of Hz. Mount selection has to consider the full picture, not just the primary frequency.
How Varying Conditions Affect Machine Vibration
Steady, consistent operation is only part of the full picture. Many machines pass through a range of speeds during start-up, operation and shutdown. That means they pass through frequencies that might coincide with the mount's natural frequency.
This is a well-known problem with variable-speed drives, engines that accelerate to operating speed and equipment that cycles between different load conditions. During the brief period where excitation frequency and natural frequency overlap, vibration can spike dramatically.
Vibration analysis captures these transient events. Our comprehensive tests show exactly which frequencies the machine passes through and how long it spends at each one. This allows engineers to assess whether brief resonance passes are tolerable or whether additional damping is needed.
Shock loading is another factor. Equipment that experiences sudden impacts generates vibration signatures that are very different from smooth continuous rotation. Vibration analysis characterises these events so that mounts can be selected to handle the actual forces involved.
How Does Vibration Analysis Apply in Practice
At AV Industrial Products Ltd, we work across a huge range of industries, all of which present different vibration challenges. This means we adapt and alter our analysis approach accordingly.
Power generation is one of the most common applications. Diesel and gas generating sets typically run at fixed speeds (1,500 or 1,800 RPM), which makes the frequency analysis relatively predictable. However, the forces involved are large and the consequences of poor isolation are serious. Vibration transmitted into building structures can cause structural fatigue, noise pollution and damage to other equipment.
Rail and mass transit applications are more complex. Wheel-rail interaction produces vibration across a wide frequency range, and onboard equipment (HVAC units, generators, compressors) adds frequencies on top. Anti-vibration mounts in rail and mass transit have to isolate equipment from the vehicle's structural vibration while also preventing equipment-generated vibration from reaching the passenger cabin.
The most cost-effective time to carry out vibration analysis is during the design or specification phase, before equipment is installed. At that stage, the analysis informs the mount selection directly and there's flexibility to optimise the system.
Once equipment is installed, it becomes significantly more expensive to alter or change mounting solutions. It typically involves removing the machine, sourcing alternative mounts, modifying arrangements and repeating commissioning. In some cases, structural modifications are needed to the supporting frame or foundation as well.
We regularly see situations where a modest upfront investment in vibration analysis would have avoided tens of thousands of pounds in rework. It's a fraction of the cost of getting it wrong.
How Can AV Industrial Products Help?
Our engineering team carries out vibration analysis as part of our mount selection and design process. This includes on-site vibration surveys using calibrated accelerometer equipment, FFT analysis of the captured data and interpretation of results to drive mount specification.
We also use computer modelling and simulation to predict system behaviour before hardware is committed. Our in-house testing capabilities allow us to verify that mount materials perform as expected under the conditions identified by vibration analysis.
Whether you're specifying mounts for a new equipment installation or troubleshooting vibration problems on existing machinery, vibration analysis provides the data needed to get the solution right.
To discuss a vibration analysis survey or mount selection project, get in touch with our engineering team.
