What should be done first to double-check for imbalance?

The correct approach to double-check for imbalance is to change the speed and observe vibration amplitude. By adjusting the speed of the machine, you can gather data on how the vibration characteristics change. Imbalance often becomes more pronounced at specific speeds, and observing the amplitude of vibrations at different speeds can help in identifying the nature and source of the imbalance. This method allows for a detailed analysis of how the amplitude responds, which can be indicative of issues related to imbalance in rotating machinery.

Additionally, while phase readings, visual inspections, and comparing horizontal and vertical readings can provide valuable insights, they are generally not as effective in quantifying the effect of imbalance as changing speed and monitoring vibration responses. These other methods may aid in diagnostics but do not directly isolate the effects of imbalance as clearly as observing changes in vibration amplitude at varying speeds does.