Did you know that AVT Reliability can provide in-situ balancing?

When to Use In Situ Balancing for Rotating Equipment

Imbalance is one of the most common causes of elevated vibration in rotating machinery, but it is not the only one. Before correction weights are added, the first job is to confirm that the vibration behaviour is actually consistent with imbalance rather than misalignment, looseness, bearing damage or another mechanical issue.

When imbalance is confirmed, in situ balancing allows the correction to be carried out on the machine in its normal operating environment. That can avoid unnecessary strip-down and transport while also accounting for the way the asset behaves under real running conditions.

What does imbalance look like?

A typical imbalance problem produces a strong vibration component at running speed. Depending on the asset and support conditions, engineers may also see changes in phase and vibration amplitude that point towards a rotating mass distribution problem.

That diagnostic step matters. A high 1x vibration peak can suggest imbalance, but it should not automatically be treated as proof. Condition, history, direction of vibration and phase information all help establish whether balancing is the right corrective action.

Why use in situ balancing?

In situ balancing is most useful where the rotor can be safely accessed and adjusted without removing it from the machine. Fans, blowers, turbines, process rolls, centrifuges and similar assets are common examples. Because the balancing work is completed on site, the correction reflects the real machine assembly, support structure and operating environment. It can also reduce downtime compared with removing a rotor and sending it away for workshop balancing.

How the balancing process works

The process begins with vibration and phase measurements at operating speed to determine the imbalance vector. A calculated trial weight may then be fitted to establish how the rotor responds. From that response, the engineer can calculate the location and size of the final correction weight. Depending on the rotor, a single-plane correction may be sufficient, while longer or more complex rotors may require multiplane balancing. The aim is not simply to make the vibration number lower. It is to apply the smallest practical correction that brings the machine back within an acceptable operating condition.

Correct the cause, not just the symptom

Balancing should also consider why the rotor became unbalanced in the first place. Material build-up, erosion, corrosion, damaged blades, missing weights or previous repair work can all change mass distribution.

Where practical, those causes should be addressed before or alongside balancing. Cleaning a fan impeller, for example, may remove part of the imbalance before any correction weight is required.

A pharmaceutical fan monitored by AVT Reliability demonstrated this clearly. Condition monitoring identified a high running-speed vibration peak consistent with imbalance. The impeller was cleaned and worn motor bearings were replaced, but high vibration remained after reassembly. In situ balancing was then carried out and vibration returned to acceptable levels.

Why post-balance verification matters

The final step is to repeat the vibration measurements after correction. This confirms whether the balancing work has reduced the running-speed component and whether the overall vibration condition now meets the agreed target.

Before-and-after results also provide a useful reliability record. If vibration later begins to rise again, engineers can compare the new behaviour against the post-balance baseline rather than starting from scratch.

When balancing is not the right answer

Not every high-vibration machine needs balancing. If the dominant problem is misalignment, structural looseness, resonance, bearing damage or another fault, adding correction weight may do little to solve the underlying issue. That is why in situ balancing works best as part of a wider vibration analysis process. Diagnose first, correct the confirmed imbalance, then verify the result. For rotating equipment where imbalance is genuinely the problem, that approach can reduce vibration, lower mechanical stress and avoid the downtime associated with unnecessary disassembly.