Causes of pump overcurrent
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The two water pumps, IS125-100-250, are equipped with 75KW motors and have a water supply capacity of 200 T/H; they operate in a master/backup configuration and have been functioning normally. Due to excessive vibration, a flexible coupling was installed at the pump inlet, which reduced the vibration levels. However, one of the pumps now experiences high current levels – the rated current is 134A, but it is currently at 158A. Meanwhile, the pressure gauge behind the pump has changed from a normal reading of 8 kilograms to 5 kilograms. The preliminary estimate is that the valve after the pump is damaged and cannot control the water flow, causing the pump to operate at high flow rates and resulting in high current in the motor. Currently, a temporary solution is to close the inlet valve; it has been found that the pressure can be adjusted to 7-8 kilograms, and the current level is also normal. Please help analyze: 1. Are there any other reasons? 2. Is it feasible to use the method of adjusting the inlet valve? What are the hazards?
Centrifugal pumps generally do not use inlets to regulate flow rate; cavitation may occur, but this also depends on the installation location, the static head, whether the equipment downstream of the valve can be used for control, or frequency conversion control can also be employed；
Personally, I think it might be a problem with the bearings of your water pump or that the installation clearance is too small. It is recommended to perform a dynamic balance check; shaft bending is less likely to be the cause. Another possibility is that the coupling is not aligned properly. Reducing the flow rate is indeed a correct approach, but under normal conditions, the current should not exceed the rated value, even if the flow rate is increased.
Personally, I think it has something to do with the load. If the head is reduced by 8 kilograms to 4 kilograms, then according to the characteristics of centrifugal pumps, it will result in overloading, and the current will also exceed the rated value； There are possibilities related to the bearings; it is possible to check the temperature of the bearings. The most important thing to consider is whether there are any changes in the axial direction. Changes in the position of the impeller can cause pressure changes, as well as changes in current ；
Flow is overloaded; after closing the inlet valve slightly, the pressure has risen somewhat! Closing the inlet valve too much can lead to cavitation, damaging the pump body and impeller; it’s better to get the outlet valve in proper working order and use it to regulate the flow rate!
Replying to the second floor: it’s water supply from a high-level tank, that is, backflow. The temperature of the water pump bearings is currently normal (the ambient temperature is -20 degrees; could it be that the temperature is too low, preventing an accurate measurement of the bearings’ high temperature?).
This post was last edited by Zui Yisheng on 2011-1-17 at 14:04. An increase in current leads to an increase in output power, which in turn means an increase in torque. Since P = nxM/9552 (in kw), and the motor speed remains constant, an increase in torque indicates greater resistance. This resistance can be caused by friction and is not directly related to flow rate, as pumps have their own performance curves; an increase in flow rate can result in a decrease in head, meaning a lower outlet pressure. Personally, there are many things I don’t understand; please feel free to correct me.
The high current is due to an excessive flow rate; however, based on your description, these two pumps have serious flow restriction issues, indicating a problem with their selection. It is recommended to reselect the pumps, otherwise your company will experience wasted energy consumption. . . .
Personally, I think the original poster’s analysis is correct; only the pump outlet valve has a problem； This results in an increase in pump flow rate and a decrease in head pressure ； And the power increases
If it meets the design requirements, it won’t be overloaded; high resistance over a long period will cause overload
This post was last edited by Zheji Bilei on February 24, 2011, at 09:01. I believe there are two possible causes: 1) Damage to the check valve after the pump; 2) Damage to the bearings. Either of these could lead to the situation described by the OP. Adjusting the inlet valve is only a temporary solution; otherwise, cavitation may occur, damaging the impeller. There’s one thing I don’t understand from the OP’s post: why does adding a flexible connector at the pump’s inlet reduce its vibration? Please give me some advice!