Centrifugal pumps are widely used in a variety of construction or industrial water supply and drainage applications, but many customers will find that the centrifugal pump is used for a period of time or intermittently, the discharge pressure is reduced or the head is not enough. The following is a simple analysis of the reasons why the centrifugal pump outlet pressure is reduced or the head is not enough.
1. Motor reversal
Due to the wiring, the steering of the motor will be reversed from the actual demand of the pump. In general, the steering of the pump should be observed first. If the steering is reversed, any two wires on the terminal on the motor should be exchanged.
2. The operating point is shifted to the high flow and low lift. Under normal circumstances, the centrifugal pump has a continuous downward performance curve, and the flow rate gradually increases with the decrease of the lift. During the operation process, for some reason, the back pressure of the pump is reduced, and the working point of the pump passively shifts to the low-lift and large flow point of the device curve, which causes the head to decrease. In fact, this is due to external factors such as the device. The change caused by the pump has no special relationship with the pump itself. At this time, as long as the pump back pressure is increased, such as closing a little outlet valve, the problem can be solved.
3. Speed is reduced
The important factors affecting the pump head are the outer diameter of the impeller and the rotational speed of the pump. Under other conditions, the lift of the pump is proportional to the square of the velocity. The effect of the velocity on the lift is very large, sometimes because For some reason externally, the speed of the pump is reduced, which will reduce the lift of the pump accordingly. In this case, check the speed of the pump. If the speed is not enough, check the cause and solve it reasonably.
4. Cavitation at the entrance
If the suction pressure of the pump is too low, below 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. Insufficient water intake or blocked inlet pipe If the water intake of the pump is insufficient and the water output of the water outlet is constant, the outlet pressure (head) will never reach the target value regardless of the pump operation. It must be checked whether there is enough water in the inlet pipe of the pump to enter the fire inlet and blocked by impurities.
6. Air in the pump
When the pump is inhaled a large amount of air due to insufficient water in the suction port, the pump will operate with a lot of noise and the pump body will heat up, and the outlet pressure (head) will not be reached.
7. Internal leakage
When the gap between the rotating part and the stationary part in the pump exceeds the design range, leakage will be caused inside, which is reflected by 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 inspection should be carried out to repair or replace the parts that cause excessive clearance.
8. Impeller flow channel blockage
If the flow path of the impeller is blocked, it will affect the work of the impeller, resulting in a drop in the outlet pressure. Therefore, it is necessary to remove the pump to check for foreign matter. To prevent this from happening again, a filter can be added before the pump inlet if necessary.
