Vibration troubleshooting guide
This guide is a step-by-step decision tree that will help you systematically pin down the cause of vibration in your equipment. Work through it step by step, answering the questions, to arrive at a precise "diagnosis" and choose the right "treatment".
Before you begin: make sure the equipment has been cleaned of dirt, all fastenings are tight, and the bearings are lubricated and free of critical wear.
Step 1: Measure the vibration spectrum
The first and most important step is to capture a vibration spectrum with a vibration analyser (such as the Balanset-1A). Take measurements in the radial (horizontal) and axial directions on the bearing housings.
Your key question: which peak in the spectrum is the tallest?
Step 2: Analyse the dominant peak
Question: does the peak at the rotational frequency (1×) dominate?
Compare the height of the peak at the rotational frequency (e.g. 25 Hz for 1500 rpm) with the other peaks.
Step 3: The problem is linked to the rotational frequency (1×)
If 1× dominates, the most likely cause is imbalance. Before balancing, you must rule out mechanical looseness.
Question: are multiple harmonics (2×, 3×, 4×...) present in the spectrum?
Look at the whole spectrum. Do you see a "forest" of peaks at frequencies that are multiples of the rotational frequency?
- ➡️ Yes, a "forest" of harmonics is visible. Your problem is mechanical looseness. SOLUTION: stop the machine and carefully tighten every bolted connection: the bearing fixings, the motor feet and the foundation anchor bolts. Then take the measurement again.
- ➡️ No, the 1× peak is clean and the harmonics are low. Your problem is imbalance. SOLUTION: carry out dynamic rotor balancing.
Step 4: The problem is NOT linked to the rotational frequency
If the tallest peak is not at 1×, look for other faults.
Question: is the dominant peak at 2× the rotational frequency, especially in the axial direction?
Compare the spectra taken in the radial and axial (along the shaft) directions.
- ➡️ Yes, the 2× peak is high, especially in the axial direction. Your problem is shaft misalignment. SOLUTION: balancing will not help! You need to align the shafts of the motor and the driven machine (pump, fan).
- ➡️ No, the 2× peak does not dominate. Go to Step 5.
Step 5: Analyse the non-synchronous peaks
Question: are there peaks at high frequencies that are not multiples of the rotational frequency?
Look for peaks in the mid and high-frequency range of the spectrum that are not harmonics (for example at 113 Hz or 137 Hz when the rotational frequency is 25 Hz).
- ➡️ Yes, there is a series of non-synchronous peaks. Your problem is a rolling-element bearing fault. SOLUTION: check the lubrication. Start planning to replace the bearing. Increase the monitoring frequency to track how quickly the fault is developing.
- ➡️ No, none of the above fits. If none of the steps has helped, you probably have a complex problem or a fault that requires advanced diagnostics by a specialist (for example electromagnetic problems, gearbox faults or cavitation).
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