Reasons for reduced flow and lower motor current in multi-stage centrifugal pumps
Thread Content
Our factory has an 80DG50×3 multi-stage pump. After replacing the mechanical seals at both ends of the pump shaft, the flow rate is not as high as before, and the motor current has also decreased. Previously, the feed volume was around 26 cubic meters, but now it’s only about 17 cubic meters. I’m not sure what the reason for this is. I seek advice from the experts.
What is the clearance of the mouth ring for the 3 impellers, and was the installation order of the impellers and the intermediate section reversed during reinstallation?
The impeller and the central body were not removed; only the pump shaft was taken out. It turned out that the short shaft sleeve at the drive end was missing – it wasn’t just left out during installation last time, but it’s also broken. I just took over this equipment.
You can check which of the following situations applies to your pump: 1. The suction line or inlet filter is blocked, or the mesh size of the filter is too large (the pore diameter of the filter is too small). Solution: Clean the suction line and filter or replace the filter. 2. There is gas inside the pump, or the medium’s temperature is high enough to cause vaporization. Solution: Refill the pump and remove the gas from inside it (by releasing air from the highest point before the pump’s outlet valve), ensuring that all gas is removed. Also check whether there are any leaks at the flanges of the suction line. 3. The motor is rotating in the wrong direction. Solution: Contact the electrical department to change the rotation direction. 4. The clearance between the impeller rings is too large, the impeller is damaged, or the flow channels within the impeller are blocked. Solution: Contact the maintenance team to inspect the pump, reduce the clearance between the rings, replace the impeller, or clean the flow channels within it. 5. Check whether the liquid level in the storage tank or tower is below the pump’s suction height. Solution: Wait until the liquid level in the tank or tower rises before attempting to run the pump again. 6. Another pump that shares the same inlet line as this one is currently in operation. Solution: Turn on this pump while keeping its outlet closed; then close half or two-thirds of the outlet of the other pump (if the system’s flow rate allows it), and finally open the outlet of this pump. The reason is that the inlet flow rate is low; the pump that is already in operation competes with this pump for flow, so it is recommended to increase the diameter of the inlet pipeline. 7. The outlet valve is open to a small degree, resulting in poor flow in the back route; the valve in that back route is also open only partially, the check valve there is blocked, or the valve plate of the outlet valve has fallen off. The solution is to increase the opening degree of the outlet valve, inspect the outlet valve or the check valve, and clear the pipelines in the back route
Make sure all the keys are installed; some wheels might not be rotating
Is it because there are fewer impellers installed? The difference is so large; it’s definitely necessary to take it apart and check
The impact of having a partially installed impeller on the quantity should not be that significant. I’m sorry; my previous reply was incorrect. There’s such a big difference, so it’s necessary to take it apart and examine it. Assuming that all other conditions remain unchanged
It’s possible that the rotor alignment has not been adjusted properly