Single Vibration Measurement – What Can Reveal About Your Machinery
Bearings are often blamed for machinery breakdowns. While internal manufacturing defects can sometimes cause failures, these cases are rare. More frequently, the root cause is improper installation, insufficient lubrication, or contamination. Even with a well-trained maintenance team, many hidden factors can silently degrade bearing performance — such as misalignment, bent shafts, mechanical looseness, cavitation etc.
Simply checking bearing condition and replacing them regularly doesn’t solve the real issues behind repeated failures. This is where detailed vibration analysis plays a critical role.
We would like to present several actions we take based on vibration data, helping our clients not only to prevent machinery breakdowns, but also to support warranty claims with clear, documented evidence.
Why One-Time Vibration Measurement Works:
1. Detailed Vibration Spectrum Analysis:
Performing a spectrum analysis clearly reveals signal components. This means an analyst can identify signals coming from specific rotating parts of the machine — or even from nearby equipment.
Often, machines exceed ISO-standard vibration limits. You may feel increased vibrations and consider an overhaul. But what if the cause is external? Consider the following case:
We measured Fresh Water generator Ejector pump. The measured RMS vibration value was 9.9 mm/s, let’s see what the spectrum reveals.
All signals visible in the above spectrum contribute to the total effective vibration (RMS), here 9.9 mm/s. Two dominant peaks appear at 39.5 Hz and 59.5 Hz.
The machine rotates at 3570 RPM. This equals 59.5 rotations per second, so the 59.5 Hz peak corresponds to motor rotation. The 39.5 Hz peak was initially unknown — we suspected it came from nearby equipment. To confirm, we took a measurement with the machine turned off. See the result:
As expected, no machine-related peaks were observed — only the 39.5 Hz signal from the surroundings remains.
Conclusion:
- The machine is not the source of abnormal vibration.
- It has a flexibility issue due to low structural stiffness.
High vibration values don’t always mean malfunction. Only a detailed spectrum analysis allows accurate diagnosis and the right recommendation -we proposed the installation of cantilever support to improve the machine’s stiffness.
2. Enhanced Machine Performance
Vibration measurement helps identify fundamental problems such as misalignment, bent shafts, machine looseness and others. Addressing these issues not only improves bearing life but also enhances the performance and reliability of the entire machine.
Our client has been struggling with excessive vibration with their IGG Blower 185 kW and they could only operate in very low- not sufficient burner load. Blower participates in producing inert gas by supplying the air to the burner.
Vessel crew changed the bearing already and they were considering buying a new impeller and dampers. But vibration signal revealed other sources of vibration.
The vibration readings were taken according to ISO standards with additional measurement points on fan housing and piping’s
The highest vibration level measured on the electric motor was 11 mm/s RMS, (root mean square, i.e. the effective value of vibration). while the fan recorded significantly higher values, reaching 65 mm/s RMS. The vibration spectrum from this location is shown in Figure 4. and reveals a dominant peak at 30 Hz and a secondary peak at 60 Hz, which appears to be harmonically related. See the spectrum below:
When we requested a change in the burner load, a strong peak at 30 Hz began to shift along the frequency spectrum proportionally to load change. As shown from the vibration meter data this prominent peak changed frequency from 29.5 Hz to 47.5 Hz.
Since the motor speed remained constant, the most likely cause of the excessive vibration was the combustion process, which generated pressure pulses in the pipes. These pulses induced vibrations at specific frequency, which changed with the burner load (i.e., the amount of fuel supplied). Changes in burner load affect the combustion dynamics, leading to different pressure fluctuations and, consequently, shifts in vibration frequency. This explains why the vibration frequency changed from 29.5 Hz to 47.5 Hz as the burner load varied.
3. Predictive Maintenence
By detecting and addressing hidden problems early, one-time vibration measurement facilitates effective preventive maintenance. This proactive approach reduces the risk of unexpected breakdowns and extends the lifespan of both bearings and machines.
The following example presents a spectrum from a misalignment of the electric motor of the Auxiliary Boiler feed water pump. High second harmonic (2X) indicates severe misalignment.
While misalignment can sometimes be identified visually, detecting a bent shaft could be much more difficult because sometimes the bending moment is caused by the temperature imbalance. Those symptoms are visible on vibrations spectra, and we are dealing with them often.
In summary, a single, well-executed vibration test can uncover root causes of machine issues that are otherwise invisible. It’s a cost-effective, non-invasive method to ensure long-term machine health, avoid unnecessary part replacements, and reduce maintenance costs.
4. Identification of Root Causes is cost effective
Single vibration measurement can provide valuable insights into the condition of a machine. In this case the Main Engine auxiliary blower showed unexpectedly high vibration levels during after ship delivery. Below photo presents the given blower, 154 KW and 3560 RPM
vibration values were:
Velocity: 17.262 mm/s RMS
Bearing Envelope: 28,58 m/s²
ISO standards categorize values above 9 mm/s as requiring immediate action (Class D) we mesured 17.2 mm/s
The vibration spectrum revealed a dominant frequency corresponding to the blower’s rotational speed (1× harmonic, ~60 Hz) See the spectrum.
This prominent peak at 60Hz could be caused by insufficient stiffness so the first step was to tighten on mounting bolts, but this was not the reason. Considering the fact of that the blower is new and clean. To exclude other causes, we checked natural frequency (resonance frequency) on the blower frame if is lying with motor speed with is 60Hzh. Results shown in bellow pizture exclude the presence of resonance near motor speed frequency (60Hz).
After tightening the bolts and confirming that resonance was not a contributing factor. We recommended submitting the impeller under warranty for rebalancing.\
5. One-Time Vibration Measurements Offers You?
A single, professionally executed vibration measurement can:
- Reveal hidden mechanical issues such as misalignment, bent shafts, and resonance, cavitation, looseness and many other
- Identify whether vibrations originate internally or from nearby equipment.
- Prevent unnecessary part replacements and reduce overall maintenance costs.
- Support data-driven decision-making in maintenance strategy.
- Extend the lifespan of bearings and machinery.
When Is a One-Time Vibration Measurement Especially Useful?
A one-time vibration measurement can deliver significant value in specific operational contexts. Some of the most effective moments to perform such a diagnostic include:
- Before shipyard docking or dry-docking:
Performing vibration analysis just before the vessel enters a shipyard allows maintenance teams to identify hidden issues in advance. This enables proper planning of repair work during the scheduled downtime and avoids costly return visits later on. - After mechanical repairs or bearing replacements:
It verifies whether the repair was successful and checks for new issues such as imbalance, misalignment, or mechanical looseness that may have been introduced during assembly. - When abnormal noise or vibration is detected:
If a machine starts behaving unusually but visual inspection reveals nothing, a single vibration measurement can pinpoint the root cause—quickly and precisely. - During commissioning or equipment acceptance such as vessel delivery:
It helps detect factory defects, improper mounting, or resonance problems before the equipment is put into operation.
- When costly component replacements are being considered:
If a team is about to replace an impeller, fan, or dampers, vibration analysis can confirm whether these components are truly the cause of the issue—or whether the root cause lies elsewhere.
Senior Service Reliability Engineer
Artur Zubiak
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Rotating Machinery Vibration Measurement – Info-marine