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Alignment of Pumps & Shafts

One of the most important parts of pump setup is making sure that the pump and the drive motor are carefully aligned. Misalignment may account for over 50% of malfunctions in rotating machinery, leading to problems such as worn or broken couplers, vibration, and excessive wear of bearings, seals and wear rings. Excessive misalignment can even cause breakage of mounts or pump/motor casings.
Once the pump set has been properly installed, the final alignment can be checked and, if necessary, corrected. Obviously, re-alignment is needed whenever the pump or motor are moved or replaced.

What do we mean by ‘alignment’?
Long-coupled pumps have a separate pump and motor shafts that are connected through a coupler. Ideally, these two shafts will be exactly parallel and have exactly the same centre-line. Flexible couplers can tolerate small alignment errors, but for smooth, trouble-free running, it is important to ensure that these two shafts are lined up to within the tolerances specified by the pump, motor and coupler manufacturers.

Causes of Misalignment
  • Movement of one piece of equipment relative to another due to thermal growth in one or both machines.
  • Piping strain or strain induced by electrical connections.
  • Torsional movement taking place at start-up or while operating.
  • Movement or settling of the foundation or baseplate.
  • Inaccurate or incomplete alignment procedures (human error).
  • Misboredcouplings.

Anyone of the above conditions will dramatically affect the alignment of equipment. If more than one of the conditions exists, the odds are highly against a machine running smoothly, quietly, or for any appreciable amount of time. Only after all of the situations have been examined and corrected can a craftsperson be assured of an accurate alignment job being achieved and maintained.

Types of misalignments:
  1. Parallel misalignment (also known as offset)
  2. Angular misalignment (also known as gap)
  3. Combination misalignment.

Parallel misalignment occurs when the shafts are parallel, but the centrelines are displaced vertically or horizontally with respect to each other.

Angular misalignment occurs when the centrelines of the motor shaft and the pump shaft are at an angle to each other.

Combination misalignment: Improperly aligned machines will typically suffer from a combination of angular and parallel misalignment.


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