Problems with the use of multi-stage centrifugal pumps
Thread Content
Our unit has three multi-stage centrifugal pumps, oil supply pumps, using diesel No. 0. Model: 65AY50x9. The nameplate indicates a flow rate of 22.3 T/h, a head of 420 m, and a rated current of 134 A for the motor. One variable-frequency unit and two fixed-frequency units. The variable-frequency pump failed and was sent for repair; a regular-frequency pump was put into use, with an outlet pressure of 3 MPa and a flow rate of around 10 T/h. The outlet opening is very small; when it is increased, the motor experiences overcurrent, and the thrust bearing’s temperature rises rapidly, exceeding 90 degrees
If the outlet opening is large, the load is high, and the current should increase
Is there a balance disc? It seems like the clearance of the balance disc has increased
The view that it’s related to the third floor is supported; such problems are common with these domestic multi-stage pumps. When the pump is started, a large pressure difference exists at both ends, which causes the shaft to shift, leading to shaft misalignment and pressure being applied to the balance disc. It is recommended to check whether the balance tube is blocked, to disassemble the pump to verify if there is shaft misalignment, to inspect the balance disc, as well as the bearings or bearing shells – it’s possible that all of these issues are present.
Suspicion of a mismatch. In terms of operation, there are oil injection mode and circulation mode. The pump is designed for oil injection operation, and is used for circulation under normal conditions. By checking the pump’s performance curve, the minimum head is above 4.2 MPa, while the actual system pressure is 3.0 MPa. What’s confusing is that excessive current indicates a large load and a small pump; however, after using variable frequency to reduce the speed, both the flow rate and head decrease, and as a result, there is no more excessive current
Are the throttling control of the outlet valve and the backflow control of the outlet pipe effective in the same way?
After frequency conversion, the current definitely shouldn’t exceed the limit; the resistance in the outlet pipeline is reduced. But if the flow rate doesn’t exceed the limit, then the current should also not exceed it, right?
If the bearing temperature is high, determine whether there is a fault
It is normal for the flow rate to be low when the valve opening is small, but a low outlet pressure, i.e., low head, high bearing temperatures, or even excessive current in the motor are all abnormal conditions; such situations should be sent for repair immediately. As for the cause of the fault, the opinion expressed on the 3rd floor is initially accepted. It is recommended that the poster provide feedback on the specific situation after the maintenance of the multi-stage pump. Thank you!
This post was last edited by “Never be mediocre” on July 2, 2016, at 20:28. The excessive current in the multi-stage pump is caused by wear on the balance disc. Additionally, the high temperature of the thrust bearing indicates that the bearing is subjected to significant axial thrust, which may lead to wear on the balance disc and subsequently cause excessive motor current. It is recommended to disassemble and inspect the pump, replace the balance disc, adjust its clearance, and also check for any other factors contributing to the excessive axial force