1.No liquid supply after startup

       (1) Check the power supply. Verify that the pump is on. Check whether the current is normal and whether the pump shaft is rotating.

       (2) Check the discharge pressure. If the pointer of the discharge pressure gauge does not move, and the water test cock does not release water, it means that the liquid has not entered the pump at all. reasons may be:

       ①Insufficient water diversion.

       ② Air leakage from the suction pipe or shaft seal.

       ③ The suction pipe is exposed to the liquid level.

       (3) Check the suction pressure. If the suction pressure gauge indicates a large vacuum degree, it may be that the suction vacuum degree has exceeded the "allowable suction vacuum degree", so that the pump cannot normally suck the liquid. Possible reasons are:

       ① The suction process is too large.

       ② The flow resistance of the suction pipe is too large, such as the filter is blocked.

       ③ The suction pipe is blocked, such as the suction valve is not opened, the bottom valve is rusted or the suction pipe is blocked, etc.

       ④ The temperature of the suction liquid is too high, resulting in less vacuum allowed to be suctioned.

       (4) If the reading of the suction pressure gauge is basically normal and the discharge pressure is lower than the normal value, there is water released from the water test cock. It means that the liquid has entered the pump, but the lift cannot meet the requirements. The reason may be in the pump:

       ①The impeller is loose.

       ②The impeller is clogged or damaged seriously.

       ③The speed is too low.

       (5) If the suction and discharge pressures are normal, but the pump still cannot discharge liquid, the reasons may be:

       ① The discharge valve is not open.

       ②The static pressure of the pipeline is too high.

       ③The lift of the other pump is too high when used in parallel.

2. Insufficient traffic

       According to the analysis of the working condition characteristics of the centrifugal pump, it can be seen that the root cause of the insufficient flow rate is the working point moving in the direction of small flow. The reasons that cause the operating point to move in the direction of small flow are:

       (1) The head characteristic curve of the pump is reduced, the reasons may be:

       ①The speed is not enough.

       ②The impeller is damaged or blocked.

       (2) The characteristic curve of the pipeline becomes steeper or moves upward. The reasons may be:

       ①The static pressure of the pipeline increases, such as the increase of the discharge height or the increase of the discharge liquid surface pressure.

       ②The resistance of the discharge pipe becomes larger, such as the discharge valve is not fully opened, etc.

       (3) The failure of the pump or piping system may be caused by:

       ①The leakage of the stopper ring wear increases.

       ②The phenomenon of cavitation occurred during the operation of the pump.

       ③ Air leakage from the suction pipe or shaft seal.

       ④ The suction pipe is immersed in the liquid level too little to inhale gas.

3. Motor overload

       (1) Check whether the power supply is normal:

       ①Check whether the voltage is normal. When the voltage decreases, the current will increase, and the motor power will not actually increase at this time, which is called superficial overload.

       ②Check whether the frequency is normal. If the current frequency increases, the speed of the motor will increase proportionally, and the shaft power of the pump will increase.

       (2) Check whether the friction power of the pump is too large. If the crank is heavier than normal, the reasons may be:

       ①The packing gland is too tight or the mechanical shaft seal is not installed properly (the spring is too tight).

       ②The pump shaft is bent or misaligned.

       ③The impeller is rubbed.

       ④The bearing is seriously worn.

       (3)Check whether the viscosity and density of the liquid to be transported exceed the design requirements.

       (4)Check whether the impeller is installed backwards. If the impeller is installed backwards, the back-curved vanes become forward-curved vanes, also overloading the pump.

       (5) If the above inspections are normal, the connection between the pump and the motor can be disconnected, and the motor can be operated independently. Check whether the motor is overloaded due to the failure of the motor itself (such as rotor friction, phase loss, etc.).

4. Excessive vibration and abnormal sound during operation

       The reasons for the excessive vibration and abnormal sound when the centrifugal pump is running are:

       (1) Mechanical reasons:

       ①The rotating parts are unbalanced. For example, the dynamic balance of the rotor after welding repair is unqualified; the impeller is partially corroded, worn or fouled.

       ② The moving and static parts are rubbing against each other. Such as pump shaft bending; bearing wear; axial thrust balance device failure.

       ③The pump base is not good. Such as loose anchor bolts or insufficient rigidity of the base.

       ④Cause the pump shaft to miss the center. Such as poor coupling alignment or improper piping installation.

       ⑤ The prime mover itself vibrates.

       (2) Cavitation occurs. The vibration and noise frequency caused by cavitation is high (600~25000Hz), which is usually generated when the flow rate is large. You can check whether the suction vacuum is too large to help judge. If it is confirmed that the vibration and noise caused by cavitation can be eliminated by reducing the flow (such as closing the discharge valve or reducing the rotation speed), reducing the liquid temperature or increasing the flow and suction.