Seeking advice on the issue of high vibration when the water pump outlet valve is not opened
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A new circulating water pump has been installed in the power plant; both the pump body and the motor are equipped with vibration meters, along with remote protection (shutdown at 7.1 mm/S). Three pumps: one variable-frequency pump and two fixed-frequency pumps. The two fixed-frequency pumps shut down as soon as they start operating (vibration exceeding 10 mm/s), while the variable-frequency pump functions normally. To reduce the starting current, the outlet valve of the water pump is generally opened after it starts operating. After the protection was removed from the two power-frequency pumps and the outlet valves were fully opened, the vibration returned to normal. May I ask why there is significant vibration when the water pump starts with the outlet valve closed? Without changing the power-frequency starting method, is there a more reasonable way to address vibration?
The water pump starts with the outlet valve closed, preventing the fluid inside from flowing out; this results in the fluid hitting repeatedly, causing significant vibration. This is because the fluid inside the water pump rotates at high speed due to the power of the rotor impeller. When the outlet valve is closed, these rapidly rotating fluids cannot be discharged, which creates high pressure and force inside the pump, thereby causing vibration. In such cases, we can adopt the following methods to reduce vibration: 1. We can slightly open the outlet valve before starting up, allowing some of the fluid to flow out, thereby reducing the impact force and pressure and thus minimizing vibration. 2. During the installation of the water pump, it is necessary to ensure that the axes of the pump body and the motor are aligned, in order to reduce vibrations caused by imbalance in the impeller. 3. A vibration damping device can be added between the pump body and the motor, which can directly absorb some of the vibrations. 4. Perform regular maintenance and inspections on the water pump to ensure that all its components are in good working condition, which can also help to reduce vibration effectively. All of the above methods can effectively address the vibration problem without changing the power-frequency starting method. .
There is a problem with your protection settings； Generally, there should be a minimum flow protection, that is, to ensure a minimum flow during startup! If the outlets are all closed, pressure buildup during startup will certainly result in high vibration levels. At such times, the duration of this pressure buildup should not be too long, otherwise the moving parts may overheat and seize up. Therefore, vibration levels will definitely be above normal at this stage; once the outlet valves are opened, the vibration levels gradually decrease, which is normal.
This post was last edited by CHANGBAISHI on 2023-11-3 08:23. It’s best to contact the design firm; vibration should not occur with variable-frequency starting. Check whether it is related to the operating procedures; for example, check valves are installed at the pump outlets. The outlet valve can be opened to 5%–10%, and then the pump can be started with the speed being increased gradually. If the frequency conversion setting is set to the maximum, vibration will occur once it reaches the highest speed after startup. It might be a problem with the operating procedures; the cause could be that the startup setting for variable frequency operation is set at the highest speed. This is provided for reference only.