It has been found that pump machinists always strive to enhance efficiency and prolong the lifespan of their pumps. Therefore, it is imperative to consider the issue of appropriate alignment of the pump shaft to achieve cost savings. If the shaft is misaligned, it can cause bearing failures prematurely, increase power consumption, and increase operating costs. To address this concern, let’s explore the proper way to align a shaft and the level of acceptable pump misalignment.
Alignment Of The Motor Shafts And Pump
To begin with, a pump’s mechanism involves transferring rotational force from a motor to the pump shaft via a coupling, which then sets the impeller in motion, resulting in fluid movement. Therefore, ensuring a minimal deviation between the pump and motor shafts is imperative.
Misalignment can manifest in the vertical and horizontal planes and angular form within these planes. A visual aid demonstrating this can be found below. Operating a pump with shafts not in proper alignment creates undue pressure on the motor and pump bearings, producing vibrations and rapidly leading to seal failure.
Pump Misalignment And Its Types
Pumps must be properly aligned during installation or gradually become misaligned over time. Unfortunately, there is a misconception in the industry that aligning a pump in the factory obviates the need for realignment during installation. This is false and can result in rapid pump failure and considerable distress onsite.
Even though the pump skid may seem robust, the base can easily bend and shift, while the motor can be displaced during installation. Consequently, it is essential to perform onsite alignment of the pump after all pipework has been installed.
Additionally, pumps may need to be more aligned for various reasons, including changes in pipework, ground subsidence, vibration, and other factors. For this reason, the maintenance team must be given time and access to realign pumps onsite periodically.
Identification Of Pump Misalignment
Two techniques are available to detect misalignment or gradual misalignment during pump operation. The first approach involves observing wear and failures in bearings and seals. Unfortunately, this method needs more scientific rigor. The operator may only recognize that a bearing, especially the Drive end bearing, has failed prematurely and may recommend checking the shaft alignment.
The other approach, which is more scientific and recommended for all sites, is to conduct vibration analysis. By using a vibration analysis meter, the operator can assess the vibration patterns occurring in the bearings. Then, by analyzing the frequency of those vibrations, the operator can identify the underlying issue, whether it’s bearing failure, misalignment, cavitation, or something else. Each vibration pattern is unique to a common issue and can help pinpoint the problem more accurately.
The Procedure Of Pump Alignment
There exist three different tools to carry out the task of shaft alignment. The least efficient method involves using a straight edge and feelers, which can be utilized for quick checks to determine if the equipment is nearly aligned. We examine both alignment planes and adjust the motor until both sides have an even gap.
The next best option is to use a pair of Dial Indicators, the preferred method for precise shaft alignment for several years. To utilize this approach, we affix a dial indicator to the motor’s shaft, then operate the measuring pin on the pump coupling. As the motor rotates, the pin moves up and down, indicating both planes’ high and low areas. We can also verify angular misalignment by shifting the dial indicator pin to the coupling faces. This method is exceptionally accurate, although it can be very time-consuming for inexperienced operators and may require extensive rework if they need to adjust the readings appropriately.
The most efficient technique for pump shaft alignment is laser alignment. This method involves affixing a laser and a mirror to one shaft. Both shafts are then rotated in tandem, and the computer built into the system determines the necessary adjustments to align the pump. Laser alignment is the sole method they utilize and approve for many locations.
Alignment Order
To avoid rework, the sequence in which we correct each plane’s four alignment variables (vertical, horizontal, and angular alignment) is crucial, as previously discussed. The initial correction is always the vertical angular alignment. This guarantees that the motor is aligned in a parallel fashion with the pump. To rectify this, we may have to insert shims on the front or rear foot to obtain a parallel reading.
The second step involves correcting the vertical alignment, which always precedes the horizontal adjustment. Since you must physically elevate the motor to modify shims, it is necessary to undertake vertical alignment before horizontal. Otherwise, after making vertical adjustments, horizontal correction must be repeated.
Once the pump and motor are at the same height, we can use jacking bolts to fine-tune the motor’s position in the horizontal plane, ensuring that it is parallel and concentric with the pump shaft.
Points To Remember For Beginners
- To avoid any further movement of the motor, it is advisable to take measurements AFTER the bolts have been tightened, as tightening the bolts may cause the motor to shift again.
- Before aligning the pump, install and tighten the pipework since it can cause the pump to shift during installation.
- After the pump is aligned, the jacking bolts will be removed or loosened.
- If the pump operates with hot fluid, it is crucial to realign it immediately after use, as it may become misaligned due to thermal growth.
- Before alignment, ensure that the pump base is securely fastened and grouted, as a warped base can ruin an otherwise excellent alignment.
How Is Near Sufficient?
Installers frequently refer to coupling specifications and assume that since a coupling can tolerate 2-3mm of misalignment, they do not need to align the shafts any closer. However, the capability and the recommended practice are two distinct matters. The closer the alignment of the shafts, the higher the likelihood of ensuring a prolonged service life, reduced power losses due to inefficiency, and an overall better operating experience with the equipment.
The guideline is to align the shafts within a maximum of 0.05mm. However, in the case of high-speed pump operation, it may be necessary to restrict this to 0.02mm in all directions.
Conclusion
Proper pump shaft alignment is essential for the efficient operation of industrial pumps. However, misalignment can cause numerous problems, including vibration, premature wear and tear, and increased energy consumption. Misalignment can be detected and corrected using appropriate alignment techniques and tools, such as dial indicators, laser alignment systems, or reverse dial indicators.
Different types of misalignment, including parallel, angular, and combined, require different alignment techniques to achieve optimal performance. Implementing proper shaft alignment techniques and monitoring alignment regularly can extend the lifespan of pumps, reduce maintenance costs, and improve overall system reliability.
