Compressor vibration diagnostics: how to read the spectrum and when to raise the alarm
Vibration is the earliest and most honest signal of a compressor's condition. It builds up long before a failure, and the spectrum reveals exactly what is wearing out. We break down what is measured and how, how to read the spectrum and when it's time to stop the machine.
What is measured and how
The main parameter is vibration velocity (mm/s RMS) per ISO 20816; vibration acceleration is used to assess bearings, and vibration displacement for low-speed machines. Sensors are mounted on the bearing supports in three directions. What matters is not a single figure but the trend relative to the original "healthy" baseline.
How to read the spectrum
The spectrum breaks vibration down by frequency and points to the cause. A component at running frequency (1×) is imbalance; the doubled frequency (2×) is misalignment; high-frequency bearing frequencies mean bearing wear; blade and tooth-mesh frequencies indicate problems in the flow path or the rotor pair.
Thresholds and trend
ISO 20816 defines zones A/B/C/D by absolute level, but the dynamics decide. A sharp rise over a short period is more dangerous than a steadily elevated but unchanging level — it is the rate of change that warns of a breakdown.
What can be fixed without opening the machine
- misalignment — by aligning the shaft line;
- loose mountings — by tightening and restoring the supports;
- imbalance — by balancing the rotor;
- bearing wear and rotor deformation — only by opening up and repairing.
A single measurement tells you little. Establish a baseline vibration signature on a healthy machine and compare against it.
The trend matters more than the absolute value. Together with oil analysis, vibration diagnostics gives the full picture of wear.
Want to set up vibration monitoring?
A QANSAT ENERGY engineer will help capture the baseline signature, set up periodic measurement and interpret your compressor's spectrum.
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