Machinery and Equipment Troubleshooting Flashcards

An overhung fan shows high 1X in both radial and axial directions, with axial phase readings in phase across both bearings. What is the most likely cause?

Answer: Overhung rotor unbalance

Overhung unbalance typically produces high 1X radial and axial vibration with in-phase axial readings.

Across a flexible coupling, axial 1X phase readings differ by about 180 degrees and axial amplitude is high. What does this indicate?

Answer: Angular misalignment

Angular misalignment produces strong axial 1X with roughly 180-degree axial phase shift across the coupling.

A shaft shows dominant 1X axial vibration, and axial phase measured at the two bearings of the same rotor is about 180 degrees apart. Which fault is most likely?

Answer: Bent shaft

A bent shaft causes high axial 1X with opposing axial phase at each end of the rotor.

A spectrum shows many running-speed harmonics plus half-order harmonics (0.5X, 1.5X, 2.5X), and phase readings are unstable. What is the most likely fault?

Answer: Rotating looseness (Type C)

Rotating looseness, such as a loose bearing fit, produces many harmonics, often with half-order components and erratic phase.

During a soft foot check, which procedure is typically used?

Answer: Loosen one hold-down bolt at a time and measure foot movement with a dial indicator

Loosening each bolt in turn while watching a dial indicator shows how much each foot lifts.

A machine with sleeve (fluid-film) bearings shows a subsynchronous peak at about 0.43X running speed. What is the most likely cause?

Answer: Oil whirl

Oil whirl usually appears at about 0.40 to 0.48X in lightly loaded fluid-film bearings.

When a rotor passes through a natural frequency during a coastdown, how does phase typically change?

Answer: It shifts about 90 degrees at resonance and about 180 degrees overall

For a single-degree-of-freedom response, phase lags 90 degrees at resonance and about 180 degrees once fully through it.