Why is the impeller ring of the centrifugal pump being held in place?
Thread Content
After repairing the motor of a variable-frequency centrifugal pump and starting it up, after one minute of operation the seal ring on the pump body and the seal ring on the impeller came together. Phenomena at that time: 1. After starting the pump, the rotational speed gradually increased; once the outlet pressure reached normal levels, the outlet valve was opened while the outlet valve of the originally operating pump was closed. 2. The outlet of the original operating pump is about to be closed; stop the motor. 3. The motor shaft has not yet come to a complete stop, and the newly started pump shuts down (there is no deceleration process; it stops instantly). I would appreciate guidance from experienced experts regarding the possible causes of the aforementioned phenomenon.
1. Excessive axial movement of the pump shaft. 2. The pump shaft is bent. 3. Impurities have entered the gap around the seal ring.
There could be reasons related to both the process and the equipment: Equipment issues include too small an annular gap and excessive axial play; process-related issues involve insufficient flow during the switching process, which leads to cavitation (check for any abnormal noises or unusual fluctuations in flow at the site)
This phenomenon needs to be analyzed from the material of the mouth ring; it is estimated that the material of your mouth ring is stainless steel!
It’s probably because the shaft movement is too large.
Just after maintenance, if various measurements were taken during the maintenance period, there should generally be no issues such as a small cold-state clearance at the collar or bending of the pump shaft; however, a recheck is still necessary to confirm this. As for the rest, it might be: regarding the equipment: check whether the mouth ring was made anew and what material it is made of What is the expansion at the medium temperature, and is the ring gap acceptable? If everything is normal, check the installation position of the pump shaft to see if there is any axial movement Did any impurities get in during the pump reinstallation? In terms of process: whether cavitation occurs, and whether there are significant fluctuations in flow rate and pressure, etc
To correct this: shaft play has nothing to do with the biting ring; the biting ring refers to radial biting, not biting at the end face! Related to the bite ring is shaft runout!
The gap became smaller, and the shaft bent. Frictional heating.
The size of the mouth ring gap is determined by the tool’s manufacturing properties; it is not an excuse for biting the mouth ring； A large axial play has nothing to do with the snap ring! This pump is operating normally; it just seizes when stopped, and it seems to have nothing to do with cavitation.
It’s most likely due to the presence of impurities; I’ve encountered this issue a few times. The solution is to grind the mouth ring – grind away 20 microns from one side of the impeller’s mouth ring
A bent pump shaft, too small an clearance between the ring seals, the presence of contaminants, and excessive movement can all be reasons that cause the ring seals to get stuck
Due to the small gap between the ring and the pump components, the pump is in a cold state during maintenance, so the gap is appropriate. However, once the medium is introduced, the temperature rises, causing the pump impeller and the ring to expand due to heat, which reduces the gap between them. Additionally, poor shaft alignment leads to the ring becoming stuck in place'； Of course, if the medium is dirty and impurities get into the mouth ring, it can also cause the mouth ring to \"lock up\".
Possible causes: 1. The gap between the mouth ring and the impeller is too small. 2. There are large hard objects in the medium that prevent the impeller from rotating. 3. No interference fit exists between the pump casing and the mouth ring, so the mouth ring is free to move. 4. The rotor is bent, resulting in jamming
A small gap could also be due to an inappropriate material
1. At that time, it was merely a routine maintenance check of the motor; the pump body was not disassembled in any way, and it was kept ready for use after preheating. 2. After the motor is overhauled, connect the coupling and shut down the pump. As a result, the aforementioned phenomenon occurred. (VFD-driven pump)
Since you haven’t disassembled the pump, how do you know it’s the mouth ring that’s stuck?
As I saw in my work, impurities have gotten into the high-temperature pump ring – it seems to be carbonized particles. I have already dealt with this issue three times. Take it off and repair the car again.
The students upstairs have mentioned all possible reasons, but the specific cause can only be determined by disassembling the pump. Moreover, if the pump is stuck, it could be due to the mouth ring or some other component; only by knowing the exact location and the symptoms can the cause be accurately determined. Also, were the pressure, flow rate, and current normal before the pump seized? They are all essential conditions for analyzing the reasons.
Based on what the poster described, it seems that after disassembling the pump, it was found that the impeller ring and the pump body ring were stuck together. It can only be due to a bent pump shaft, resulting from long periods of inactivity without shaft rotation.