License to Chill - September 2018
Improper shaft alignment can prove costly Many a plant inspection/survey has revealed that in almost every instance – pumps, motors, compressors, tower fans – you name the equipment, it’s almost always out of alignment. From newly commissioned equipment to plants that have been in service for years, the findings are always the same – shaft alignment is not correct.
The fact is that rotating equipment is susceptible to misalignment. Machines that are in proper alignment from day one, and subsequently well-maintained, will reduce energy consumption, reduce breakdowns and require less repair parts and labour cost.
When rotating machinery is misaligned, the loading of the shafts dramatically increases due to reaction forces created in the coupling. In addition, the equipment (Drive and Driven) will develop elevated temperatures especially around the bearing housings. This condition will cause premature equipment failure, costly repairs and increased energy consumption. Infrared Thermography inspection will detect a coupling and bearings that are operating overloaded; however it will not address the root cause of the overload (misalignment). So, IR Thermography should always be a part of the plant PM program, as it will uncover problems.
Proper shaft alignment will reduce energy consumption by as much as 10%. Proper shaft alignment will reduce mechanical seal failures by 65% and will also save 30% of equipment repairs due to misaligned equipment.
Let us look at the way most alignment is performed.
- A straight edge and feeler gauge : I have seen this method used very often. This procedure is dependent on the limited resolution of the human eye, and I would not recommend this for alignment, as it is inadequate for most equipment employed in state-of-the-art chilled water plants.
- Dial Indicators: These normally have resolution of 0.39 mill and calculations tend to be complicated, requiring highly experienced engineers. And the alignment procedure can take a very long time to accomplish. This procedure is also prone to human error, such as sticking and/or jumping dial, sagging indicator brackets, play in mechanical linkage, tilted dial indicator, axial shaft play and reading errors.
The preceding methods of shaft alignment are the most common but they are the most inaccurate. I would recommend laser alignment be a part of any chilled water plant service provider’s services and solutions. Laser alignment is straight forward. Systems are user friendly and intuitive. It is possible to quickly set up fully assembled sag free brackets. Other features are simple on-screen guidance to enter required equipment data and error free accurate measurement resolution within 0.00004”. Laser alignment has no human reading errors and bracket sag influences, and readings can be taken at any position. In addition, the laser beam can be adjusted on the screen of the alignment equipment. Reports can be generated directly from the alignment equipment, and the results are far more accurate versus the two methods described above.
The cost of shaft misalignment is very high, as again it will cost you energy and premature equipment failure. I would recommend that each and every year all rotating equipment undergo IR-Thermography and laser shaft alignment checks ; it can save any chilled water plant substantial cost.