(1) Motor reversal
Due to wiring problems, the direction of the motor may be opposite to the actual required direction of the pump. Therefore, you should first observe the direction of the pump when starting. If the direction is reversed, you should swap any two wires on the terminal on the motor.
(2) The operating point shifts to a high flow rate and low head
Generally speaking, centrifugal pumps have a continuous downward performance curve, and the flow rate gradually increases as the head decreases. During operation, due to some reason, the pump back pressure decreases, and the pump working point passively shifts to a low head and high flow point along the device curve, which will cause the head to decrease. In fact, this is caused by external factors such as changes in the device, and has nothing to do with the pump itself. At this time, you only need to increase the pump back pressure, such as closing the outlet valve a little, to solve the problem.
(3) Reduced speed
The important factors affecting the pump head are the impeller outer diameter and the pump speed. When other conditions remain unchanged, the pump head is directly proportional to the square of the speed. It can be seen that the speed has a great influence on the head. Sometimes, due to some external reasons, the pump speed is reduced, which will correspondingly reduce the pump head. At this time, the pump speed should be checked. If the speed is indeed insufficient, the cause should be checked and a reasonable solution should be found.
(4) Cavitation at the inlet
If the suction pressure of the pump is too low, lower than the saturated vapor pressure of the pumped medium, cavitation will occur. At this time, the inlet piping system should be checked for blockage or the inlet valve opening is too small, or the liquid level of the suction pool should be increased.
(5) Internal leakage
When the gap between the rotating part and the stationary part of the pump exceeds the design range, internal leakage will occur, which will be reflected as a drop in the discharge pressure of the pump, such as the impeller ring gap and the interstage gap of the multistage pump. At this time, the corresponding disassembly and inspection should be carried out, and the parts that cause the gap to be too large should be repaired or replaced.
(6) Impeller flow passage blockage
If part of the impeller flow passage is blocked, it will affect the impeller's work and cause the outlet pressure to drop. Therefore, it is necessary to dismantle the pump to inspect and remove foreign objects. To prevent this problem from recurring, a filter device can be added before the pump inlet if necessary.