Adjustment of shaft alignment in multi-stage centrifugal pumps
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The electrodialysis feed water pump used in our company is a grade-10 centrifugal pump. When it was disassembled a few days ago, it was found that the impeller on the low-pressure side was severely worn. The bearings used previously were cylindrical roller bearings; when the pump started operating, excessive shaft movement occurred, resulting in friction between the impeller and the pump casing. Since all the keyways for the impeller in this pump are aligned on one line, and the balance disc is fixed to the key without any nuts, the only solution was to use the motor to push against the pump on the low-pressure side in order to prevent excessive movement. However, this caused the motor current to be high. After adjusting the deep groove ball bearings at both ends and starting the pump again, the bearing temperatures rose, as the high temperatures were caused by the shaft movement affecting the bearings! I would like to ask the experts: how can adjustments be made, using cylindrical roller bearings, to keep the error within a reasonable range?
You should be using a DG-type multi-stage pump. Such pumps have N-type bearing housings at both ends that can be removed. The adjustment of axial displacement in these pumps is done through the balance disc; in your case, it seems that the gap in the balance disc hasn’t been adjusted properly. When adjusted correctly, the axial displacement should be around 0.5 mm. Please check carefully the gap between the balance disc and the balance ring. Even if you replace them with deep groove ball bearings, it won’t help if the gap isn’t adjusted properly, as excessive axial force will cause the bearings to burn out. Using thrust bearings won’t solve the problem either – they will also burn out as a result of the excessive axial force
That’s right; no matter how I adjust it, it doesn’t work properly. Could you tell me the method for adjusting it? Thank you
Can it be adjusted using the bearing nuts at both ends? How can it be adjusted if possible? Should the high-pressure side be tightened first before installing the low-pressure side?
N years ago, DF9 grade, optical axis, no positioning stage. It is also impossible to accurately measure the shaft runout and the balance disk runout. Research is ongoing; inquiries were made to the manufacturer, but their response was not very clear either. I’m looking for a reply letter.
Adjust the balance disc! ! ! It is necessary to adjust so that when the balance disk touches the balance ring, the position of the impeller is at the midpoint of the total stroke!
It’s not that there’s no way to measure it; it’s just that no method has been found yet
Add me on WeChat; if you can’t do it, I’ll feel even worse than you! m249898904
Let’s exchange ideas here so that everyone can learn from it.
During installation, do not install the balance disk for now; use a jacket in its place. Measure the distance a from the impeller to the front and rear cover plates – this represents the total axial displacement of the impeller. Generally, move the impeller closer to the outlet side, and then measure the distance b from the last stage of impellers to the pump’s balance disk (it is necessary that all impellers be pressed tightly together during this measurement). There is also the distance c related to the balance disk itself (some designs have a shaft sleeve in front of it). The difference between b and c should be half of a minus 0.5 mm. Each time an impeller is installed, it is necessary to check whether there is any loss in axial displacement; make sure there is no such loss after installation
First, remove the sealing boxes at both ends of the pump, as well as the bearing housings and balance rings. Then, install the balance disc, shaft sleeves (without installing seal rings), bearing caps, bearings, and round nuts in sequence, tightening them firmly. Now, let’s measure the total axial movement. First, take the mating surface between the outlet section and the sealing box as the reference plane. Push the shaft in the direction of the inlet until it can no longer be moved further. Use a depth gauge to measure the distance from the reference plane to the back side of the balance disk and record this value (assuming it is 38 mm). Next, pull the shaft in the direction of the outlet until it can no longer be moved further. Again, use a depth gauge to measure the distance from the reference plane to the back side of the balance disk and record this value (assuming it is 30 mm). By subtracting the two values from each other, the total stroke is 8 MM; the half stroke is then obtained by dividing this value by 2, which gives 4 MM. In other words, when the dimension from the reference plane to the balance disc is 34 mm, the impeller is exactly in the middle position. Next, I need to find a way to get the balance weight here first. I need to recall carefully – it’s been repaired only twice. If any experts spot anything wrong, please definitely give me some guidance!! Leading people astray isn’t a trivial matter. I hope this can help you!