Overview Of Single-stage Centrifugal Pump And Common Faults And Solutions During Commissioning

Nov 23, 2024

A single-stage centrifugal pump includes a pump body, a pump cover, an electric motor with an output shaft, a pump shaft, a bearing seat, an impeller, a mechanical seal, and a mechanical seal cover installed inside the pump body. Its characteristic is that it also includes a clamp type coupling located between the output shaft of the electric motor and the pump shaft, as well as a guide bearing installed on the bearing seat to assist in supporting the pump shaft; The clamp type coupling is rigidly connected to the output shaft of the motor and the pump shaft respectively, leaving a space distance between the output shaft of the motor and the pump shaft for easy installation and removal of the mechanical seal and the mechanical seal cover. When repairing or replacing mechanical seals, there is no need to disassemble the motor and pump cover.

When testing a single-stage centrifugal pump, it should be inspected first, then tested under no-load, and finally tested under load. Only after the test runs normally can it be delivered for use.
(1) Inspection before test drive
Before testing the single-stage centrifugal pump, the following items must be checked.
① Check for any looseness in the connecting bolts and foundation bolts of the pump.
② Is the lubricating oil for the bearings sufficient? If not, the lubricating oil should be labeled according to the requirements in the pump manual.
③ The lubrication and cooling systems should be unobstructed and leak free.
④ Uniform turning, no friction or looseness, and no noise inside the pump.
⑤ Is the power wiring correct.
After the above inspections are completed and meet the requirements, the no-load test can be carried out.
(2) Empty load test
There is no working medium in the pump, and the test run of the empty vehicle after starting is called no-load test. Empty load testing can expose some of the problems that exist during installation. During no-load testing, the following issues should be noted.
① Observe whether the direction of the electric motor is the same as the required direction of the pump. It can be observed when the motor is started or stopped. If the observation is unclear and it is difficult to determine the direction of the motor rotation, you can insert a piece of paper into the protective cover of the motor fan while the motor is running, and see the direction in which the paper is moved by the fan blades to know the direction of the motor rotation. If the direction is reversed, simply swap the two live wires of the power supply to change the direction.
② The maximum temperature of rolling bearings should not exceed 70 ℃. If there is no suitable temperature measuring instrument, the outer wall of the bearing seat can be touched by hand, preferably not too hot The touch time should not be too short, otherwise the hand cannot feel the real temperature.
③ Smooth operation without noise, and normal cooling and lubrication system. If there is significant vibration, the vehicle should be stopped to check if the coupling alignment meets the requirements. When the alignment of the coupling does not meet the requirements, it not only causes vibration, but also heats up the coupling.
(3) Load test
The steps for load testing are as follows.
① Turning the car. Attention should be paid to even weight distribution. There should be no noise or rubbing inside the pump.
② Pump filling. When filling the pump, it should be slowly turned to discharge the gas inside the impeller and volute. Pump filling is completed, close the inlet and outlet valves.
③ Open the inlet valve to the maximum flow rate, start the motor, balance the operation, and then slowly open the outlet valve until it reaches the maximum flow rate position.
It is worth noting that the outlet valve and inlet valve of the pump should not be in the open position when starting, as this will cause excessive load on the motor and may burn it out. Do not close the inlet valve and open the outlet valve to start, as this will cause excessive vacuum in the suction pipeline and result in pump cavitation.
④ Adjust the flow rate of the pump with an outlet valve and measure the performance of the pump. Observe whether its flow rate and pressure meet the requirements.
⑤ When parking, the outlet valve should be closed first to prevent liquid backflow, and then the power should be disconnected.
The requirements for load testing are as follows.
① The sealing leakage should meet the requirements, and the drip rate of the packing seal should be less than 10-20 drops per minute. The drip rate of the mechanical seal should be less than 5 drops per minute.
② The temperature rise is normal and the operation is stable. When measured with a portable vibration meter, the bearing vibration should be less than the values specified in Table 2-22.
③ The flow rate and pressure can meet the requirements and are relatively stable.
④ The current does not exceed the rated value.
⑤ Operate continuously for 4 hours.
(4) Acceptance check
① The maintenance quality meets the prescribed requirements, and the maintenance records are complete and accurate.
② After passing the trial run and performance test, the pump shall be accepted according to regulations and delivered for production use.
The transmission mode of the pump is connected to the electric motor through an extended elastic coupling, and the rotation direction of the pump is clockwise when viewed from the driving end. Mainly applicable to industry, agriculture, urban areas, drainage, fire water supply, etc.