Alignment Shaft

In the last issue, we discuss about shaft seals and how liquid is prevented from coming out from the pump housing even though the shaft is rotating.

Some mechanical seals are made to very fine tolerances. Damage to mechanical seals and bearings can sometimes be cause by the misalignment of pump shaft with the motor shaft.
Whenever some of the motors or driven machinery is dismantled or even when the machines are not running smoothly, alignment has to be done.
The purpose of alignment is to ensure that the centerline of the motor rotor shaft coincides exactly with the centerline of the driven machinery. Alignment is essential to ensure that the machine runs smoothly with minimum vibration.
Provided the two shafts are not bent crooked, the two alignments to be checked and adjusted are: Offset alignment and Angular alignment.
Most alignments are rough alignment that can be done using straight edge ruler and feeler gages. However for precision alignment, the use of dial gauges with magnetic bases can be used.

Offset Alignment
The radial alignment is checked using a straight edge ruler. By placing the ruler across the coupling halves at the top, bottom and both sides any gaps between the 2 coupling halves will indicate that the shaft is offset slightly. The misalignment can be corrected by shifting the motor or by putting shims to raise up the motor or driven machine.

Angular alignment
By inserting a feeler gauge between the coupling faces and rotate both coupling halves simultaneously we can check whether the shafts have any angular displacement between them. The feeler gauge readings at checked at four points on the shaft coupling. Again the alignment is corrected by shimming or shifting the machinery.
The motor and the driven machine should be bolted solidly to the base after finalizing the alignment positions of the equipment.