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Contributor: James Farley, Griswold Product Manager, PSG
Welcome to the centrifugal pump minute! Today’s topic is coupling alignment. My name is James Farley and I’m a Product Manager with Griswold.
Coupling misalignment is one of the key sources of vibration and centrifugal pumps. Yet, we can control it by proper alignment. Today, we’re going to talk about what that process is. Before starting coupling alignment, we need to check the whole installation for some key requirements. This is going to include having a rigid foundation or base flight for the pump and motor to be mounted to. Additionally, we need to make sure that the piping is going to be aligned with the pump so that we minimize nozzle loading. If we have issues here we need to fix them before we move into coupling alignment. It’s also important to conduct alignment when the pump is at normal operating temperature. The pump and the piping will go through thermal expansion and we need to set the alignment when we’re at that normal.
In the first step, we want to loosen all of the bolts on the pump in the motor and align the pump to the suction and discharge piping. We’re then ready to tighten the bolts on the suction and discharge and that will set the pump in position on the baseplate. In the second step, we’re now going to fully tighten the bolts on the pump and secure that pump firmly to that foundation. It’s very important to not use shims between the pump and the baseplate. Otherwise, you may get soft foot condition in the future. We are now ready to perform an alignment. We would recommend using a laser alignment tool. These tools very precisely measure the alignment of the pump shaft and the motor shaft, because there are sensors that are directly attached to each. The additional advantage is that the tool gives you guidance about how to relocate and position the motor is that it is fully aligned.
If you don’t have a laser alignment tool, alignment can still be accomplished with a dial indicator. As you see here before we go through that process I’m going to explain some of the terminologies. What steps are needed to get the motor alignment? We need to be checking both parallel and angular alignment. Angular means that the two shafts are not aligned and as an example, if the motor was tilted at a severe angle the two shafts are clearly not in angular alignment. Parallel alignment is where the two shafts are offset, yet they’re still parallel. So that can be vertical or horizontal. We need to be checking both of these in order to check angular alignment. We’re going to be using a dial indicator. If a dial indicator needs to be connected to your pump shaft and then come in contact with the face of your coupling. It’s also important to make a mark on your coupling because we need to rotate both the pump shaft and the motor shaft together to get an accurate read.
Once I have the dial indicator set I need to zero the indicator out and rotate the indicator 180 degrees with both shafts moving together. The change in reading tells you how far out of angular alignment the pump is. To demonstrate I would rotate both the motor and the pump shaft together take it to 180 degrees and measure the change in reading. If I’m measuring in the three and nine o’clock position I’m measuring the horizontal alignment of the pump. If I’m in the 12 and six o’clock positions I’m measuring the vertical angular of alignment. After adjusting the angular alignments that are within tolerance. We now need to check the parallel alignment to do this. We’re gonna take a dial indicator and place it on the outer diameter of the coupling. Again we should mark the coupling so that we know that we’re moving both shafts together. We’re gonna set the reading at 0 and rotate 180 degrees. The change in reading needs to be checked against the tolerance requirement and we need to adjust until we are within the published requirement. Again if we’re testing in the 3 and 9 o’clock positions we’re checking horizontal parallel alignment. We’re checking in the 12 and 6 o’clock position. We’re checking vertical parallel. Pump alignment is critical to minimize the vibration of the pump and maintain reliable performance. Thank you for joining us – check out our other videos on centrifugal pumps!