Shaft Alignment & Machinery Installation Flashcards

When using the rim and face dial indicator method, what does the 'face' indicator primarily measure?

Answer: Angular misalignment between the two shafts

The face indicator is placed perpendicular to the shaft axis and measures the gap variation across the coupling face as it rotates, directly indicating angular misalignment.

A machine exhibits high 1× vibration that is equal in amplitude in both the horizontal and vertical radial directions and is also high in the axial direction. This pattern most likely indicates:

Answer: Combined angular and parallel misalignment

Combined angular and parallel misalignment produces elevated 1× vibration in all three directions (horizontal, vertical, and axial) simultaneously, because both offset and angular forces act on the coupling and bearings.

What is the function of a 'spacer' or 'spool piece' in a shaft coupling, particularly for alignment purposes?

Answer: To provide axial distance between the driver and driven machine hubs, allowing removal of the coupling element without moving either machine and accommodating thermal growth

A spacer coupling maintains a gap between machine hubs so the flexible element can be removed for maintenance or bearing replacement without disturbing the aligned machines, and it also accommodates axial thermal growth.

What effect does 'pipe strain' have on a pump and its alignment?

Answer: External piping forces distort the pump casing, inducing misalignment and soft foot that will return even after correct alignment is performed

Pipe strain applies external forces and moments to the pump casing through the suction and discharge flanges; these forces distort the casing and bearing housing, creating internal misalignment that recurs each time it is corrected.

During alignment verification after tightening hold-down bolts, which phenomenon can cause the alignment to change from the pre-tightened values?

Answer: Soft foot distorting the machine frame and repositioning the shaft centerline as bolts are torqued

Soft foot causes the machine frame to flex and distort as hold-down bolts are tightened, which moves the shaft centerline position and can significantly change the alignment values measured before bolt tightening.

What is the primary advantage of laser alignment systems over traditional dial indicator methods?

Answer: Laser systems eliminate bracket sag error and provide real-time digital readout of misalignment in all planes simultaneously with higher repeatability

Laser alignment systems eliminate bracket sag (a key error source in dial indicator methods), display live misalignment values in all planes simultaneously, and provide higher repeatability because human reading errors and sag corrections are removed.

When aligning a horizontal pump-motor set, which machine is typically moved to achieve alignment, and why?

Answer: The motor (driver) is moved because the pump is fixed by its piping connections and process requirements

The motor is designated the 'moveable machine' in most pump-motor alignments because the pump is fixed in position by the process piping, its suction/discharge flanges, and the process it serves.