Shop balancing was conducted after impeller repair. Running test was carried on the result shown on table 1 was amazed everyone.
The higest vibration was 32 mm/s rms. Dominated frequency was 1x running speed, the question was “ are they really balanced this equipment?”.
Balancing document review shows that the shop consider the impeller as centerhung fan, although residual unbalance was still on tolerance for grade 2.5.
Then it was decided to rebalanced the impeller (on site), and the final result vibration drop from 33 mm/s to 2.3 mm/s.
Note : There are different treatment in balancing procedure for centerhung and overhung rotor. Failure on recognition will cause unacceptable balancing result.
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