When repairing the rotor of a multi-stage pump, should dynamic balancing be performed? How to determine this properly?
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As a technical manager, in actual on-site work, how should one properly determine whether dynamic balancing is necessary for a multi-stage pump rotor after repair, taking into account factors such as available time, the extent of damage, and the components that need to be replaced?
Personally, I think it’s necessary to perform dynamic balancing after each repair; that would be better, unless the repairs do not involve any parts related to the bearings.
Hehe, usually they are directly driven by motors, rotating at 1500 revolutions per minute. We used to not perform dynamic balancing on them, and we rarely even did static balancing. Unless there are visible defects. You think, for that small impeller, you still need to make a fake shaft
Well, in theory, all the required actions should be taken, and doing so brings only benefits with no drawbacks. But in practical work, due to other factors, it can become difficult or even impossible to perform dynamic balancing after repairs. Based on our technical experience, when faced with such situations, we need to make decisions based on solid and credible evidence. If an assessment is necessary to resolve the issue, we must proceed with it despite any difficulties related to production or costs. However, as for how to determine the threshold between doing it and not doing it, everyone is welcome to discuss actively and share their experiences.
In my opinion, it’s not necessary to perform dynamic balancing for the maintenance of centrifugal pumps; unless the impeller needs to be remachined, even if the shaft has defects, methods such as surfacing, turning, or electroplating can be used. There is no need to perform dynamic balancing; dynamic balancing is a highly precise process. Centrifugal pumps are very sensitive to such issues, as the play in their bearings is much greater than the amount of imbalance present.
If the rotor has been repaired, it’s best to do it again. In other cases, the degree of damage and any abnormalities in operation are determined by visual inspection.
I think it’s necessary to first check other parameters such as bearing clearance, bushing clearance, and radial runout. If there are no issues with these, then rotor dynamic balancing may not be necessary. After the pump starts operating, it’s important to monitor whether the vibration levels increase rapidly over a short period of time; if the vibration levels are high, then dynamic balancing should be considered.
For routine maintenance, it is not necessary to perform dynamic balancing on the rotor; simply using a dial indicator to check its runout is sufficient. However, if there are issues with the rotor or impeller that have been repaired, dynamic balancing is required.
Generally, we don’t do that. If the pump is repaired due to vibration issues, the decision is made based on the results of the repairs; usually, bearing damage or impeller cavitation problems do not affect the balance of the shaft. If it is caused by significant mechanical friction, it should be addressed. Personal opinion
Most imbalances in multi-stage pumps stem from the cast impeller; therefore, if the impeller is not replaced or its position is not changed, it is often not necessary to perform dynamic balancing during the repair of such pumps. If the impeller is replaced, or if its order is changed, or in the case of high-speed, large-scale multi-stage pumps, dynamic balancing should be performed during maintenance.