On-site balancing reduces rotor unbalance while the rotor remains installed in its operating machine. Instead of removing the rotor for workshop balancing, vibration amplitude and phase are measured during controlled machine runs and correction mass is applied at suitable accessible locations.
When on-site balancing is useful
On-site balancing can be practical for installed fans, blowers and other rotating equipment where rotor removal is difficult, where the assembled condition contributes to the balance state, or where a final trim balance is required after installation.
- Installed industrial fans and blowers
- Rotating assemblies that are difficult to remove for workshop balancing
- Machines where the final assembled condition influences balance
- Final trim balancing after repair, overhaul or rotor replacement
Conditions required for a useful balancing run
The machine must be capable of safe, repeatable operation. A useful on-site balance normally requires stable speed, repeatable vibration, a reliable rotational phase reference and safe access to a correction plane.
- Stable operating or test speed
- Repeatable 1× running-speed vibration and phase
- Usable tachometer or phase-reference location
- Accessible correction positions
- Safe start, stop, isolation and access procedure
- Customer operator or authorised personnel available where required
Balancing is not a substitute for vibration diagnosis
High vibration is not automatically caused by rotor unbalance. Misalignment, looseness, bearing defects, resonance, rubbing, shaft or fit problems, structural flexibility and aerodynamic or hydraulic forces can produce similar symptoms. If the vibration response is not sufficiently consistent with unbalance, RDB may recommend diagnosis or mechanical correction before balancing.
Typical on-site balancing process
- Review the machine, operating condition and site safety requirements.
- Measure baseline vibration amplitude, phase and running speed.
- Apply a controlled trial weight where the rotor and correction location permit.
- Calculate the required correction magnitude and angular position.
- Install the agreed correction using a mechanically suitable method.
- Run the machine again and verify the resulting vibration.
Single-plane and two-plane work
Some installed rotors can be corrected effectively in one plane. Wider or longer rotors may require two-plane correction, but this depends on rotor behaviour, available correction planes, sensor access and whether the machine can provide sufficiently repeatable measurements. The balancing approach is selected from the actual machine response rather than from rotor type alone.
Correction methods
Correction may use approved balance weights, existing balance holes, bolted weights or another mechanically suitable method agreed for the rotor. Welding, grinding or drilling is only considered where the component, access and customer requirements make the method appropriate and safe.
Information to send before arranging a site visit
- Machine type and application
- Rotor, fan or impeller description
- Normal operating speed and whether speed is stable
- Recent vibration readings, spectra or reports if available
- Photographs of the machine, rotor access and possible correction locations
- Whether a shaft keyway, reflective tape or other phase-reference location is accessible
- Site location, access restrictions and permit requirements
- Any known mechanical faults, recent repair or process-related vibration changes
Site safety and operating responsibility
On-site balancing requires controlled machine operation and repeated access between runs. The customer remains responsible for site isolation, permits, safe access, guarding arrangements and operation of the machine unless otherwise agreed. RDB may stop the work if the machine response is unstable or the correction process cannot be carried out safely.
Verification and report
The final result is verified from the measured running condition. Where agreed, the service record can include the baseline condition, trial/correction information and final vibration measurements. The result applies to the machine condition and speed tested during the site work.
Workshop balancing or on-site balancing?
Workshop balancing is generally preferred when the rotor can be removed and mounted repeatably on a balancing machine, because the rotor unbalance can be measured independently of many installed-machine effects. On-site balancing is useful when removal is impractical or when the assembled machine condition itself needs final trim correction. RDB can review the application and advise which route is more appropriate.