1) Motor reverse
Due to the wiring reasons, the rotation direction of the motor will be opposite to that of the pump. Generally, the rotation direction of the pump should be observed when starting. If the rotation direction is reversed, any two wires on the terminal of the motor should be exchanged.
(2) The operating point shifts to large flow and low head
In general, centrifugal pumps have a continuous downward performance curve, and the flow rate gradually increases as the head decreases. In the process of operation, due to some reasons, the pump back pressure is reduced. The working point of the pump passively shifts to the low-lift and large-flow point with the device curve, which will cause the head to decrease. In fact, this is due to external factors such as the device. The result of the change has nothing to do with the pump itself. At this time, the problem can be solved by increasing the back pressure of the pump, such as closing a little outlet valve.
(3) Speed reduction
The important factors that affect the pump head are the outer diameter of the impeller and the speed of the pump. Under other conditions unchanged, the head of the pump is proportional to the second power of the speed. It can be seen that the impact of speed on the head is very large, sometimes because Some external reasons reduce the speed of the pump, which will reduce the head of the pump accordingly. At this time, check the speed of the pump. If the speed is indeed not enough, check the reason and solve it reasonably.
(4) Cavitation at the entrance
If the suction pressure of the pump is too low, lower than the saturated vapor pressure of the pumped medium, cavitation will form. At this time, check whether the inlet piping system is blocked or the inlet valve opening is too small, or increase the liquid level of the suction pool.
(5) Internal leakage occurs
When the gap between the rotating part and the static part of the pump exceeds the design range, it will cause internal leakage, which is reflected in the drop in the discharge pressure of the pump, such as the gap between the impeller mouth ring and the interstage gap of the multi-stage pump. At this time, the corresponding disassembly and inspection should be carried out, and the parts that cause the excessive clearance should be repaired or replaced.
(6) The impeller flow passage is blocked
If part of the flow passage of the impeller is blocked, the work of the impeller will be affected and the outlet pressure will drop. Therefore, it is necessary to disassemble the pump to check and remove foreign objects. To prevent this problem from recurring, if necessary, a filter device can be installed before the pump inlet.
