Problem
9.8 mm/s VibrationMethode
Balanset-1A 1-plane AuswuchtenErgebnis
0.9 mm/s in 25 minBackground
A colocation data center in the Netherlands operates four induced-draft cooling tower fans running 24/7 to dissipate heat from 1,200 server racks. Each fan — an axial unit with six blades at 720 RPM — sits on the roof directly above the server hall. After two years of continuous service, scale deposits and minor blade erosion created progressive imbalance. Vibration at the drive-end bearing reached 9.8 mm/s RMS, exceeding ISO 10816 Zone C and causing audible low-frequency hum in the server room below.
The facility’s SLA mandates 99.99% uptime. Removing the fans for shop balancing was not an option during the cooling season. In-situ balancing with Balanset-1A was scheduled during a maintenance window.
Setup
Work proceeded on Unit 3, the worst-affected fan. The VFD was locked to 720 RPM. One piezoelectric sensor was magnetically mounted on the motor drive-end bearing housing. A reflective tachometer strip was placed on the shaft coupling. Fan guard panels were opened but the rotor remained mounted.
Measurement Procedure
Run 1 — Baseline
Vibration: 9.8 mm/s RMS at 1× RPM. No significant 2× component, confirming imbalance rather than misalignment.
Run 2 — Trial weight
A 45 g trial weight was bolted to one of the existing balance bolt holes on the fan hub at the 0° reference. Balanset-1A computed the correction vector.
Run 3 — Correction
Correction: 32 g at 228°. Installed using a steel washer and M8 bolt in the nearest hub hole.
Final vibration: 0.9 mm/s RMS — well within Zone A. Sound-level meter readings at the server floor dropped by 14 dB at the dominant tone.
Result
Unit 3 was balanced in 25 minutes. The remaining three fans were completed in the same shift. Bearing temperature on Unit 3 dropped 11 °C within two hours, indicating significantly reduced radial load.
"We balanced all four fans in one shift — the server room is finally quiet"
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