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1. What is the main working principle of a centrifugal pump? The motor drives the impeller to rotate at high speed, causing the liquid to generate centrifugal force. Due to the centrifugal force, the liquid is thrown into the side channel and discharged out of the pump, or into the next-stage impeller, thereby reducing the pressure at the impeller inlet and forming a pressure difference with the pressure acting on the suction liquid. The pressure difference acts on the liquid suction pump. Due to the continuous rotation of the centrifugal pump, the liquid is continuously sucked in or discharged. 2. What are the functions of lubricating oil (grease)? Lubrication, cooling, flushing, sealing, vibration damping, protection and unloading functions. 3. What three levels of filtration does lubricating oil need to undergo before use? first level: Between the original lubricating oil barrel and the fixed barrel ； Level 2: Fix between oil drum and oil can ； Level 3: Between the oil can and the refueling point. 4. What are the "five certainties" for equipment lubrication? Fixed point: Refuel according to regulations ； timing: Lubricate the lubricated parts according to the specified time and change the oil regularly ； Quantitative: Refuel according to consumption ； qualitative: Choose different lubricants according to different machine models and keep the oil quality up to standard ； Determine the person: Each refueling position must be handled by a dedicated person. 5. What are the dangers of water in the pump lubricating oil? Moisture can reduce the viscosity of lubricating oil, weaken the strength of the oil film, and reduce the lubrication effect. Water freezes below 0°C, seriously affecting the low-temperature fluidity of lubricating oil. Moisture can accelerate the oxidation of lubricating oil and promote the corrosion of metals by low molecular organic acids. Moisture will increase the foaming properties of lubricating oil, making lubricating oil prone to foaming. Moisture can cause metal parts to rust. 6. What are the maintenance contents of the pump? Earnestly implement rules and regulations such as job responsibility system and equipment maintenance. Equipment lubrication must be "five-level" and "three-level filtration", and the lubrication equipment must be complete and clean. Maintenance tools, safety facilities, fire-fighting equipment, etc. are complete and neatly placed. 7. What are the common standards for shaft seal leakage? Packing seal: Light oil is less than 20 drops/minute, heavy oil is less than 10 drops/minute mechanical seal: Light oil is less than 10 drops/minute, heavy oil is less than 5 drops/minute. 10. Why can’t the centrifugal pump start when the disc is not moving? If the centrifugal pump disc does not move, it indicates that there is a fault inside the pump. The fault may be that the impeller is stuck or the pump shaft is bent excessively, or the dynamic and static parts of the pump are rusted, or the pressure inside the pump is too high. If the pump plate is forced to start without moving, the powerful motor force will drive the pump shaft to rotate forcibly, which will cause damage to internal parts, such as the pump shaft breaking and twisting, the impeller broken, the motor coil burned, and the motor may trip and start failure. 11. What is the function of sealing oil? Cooling seal parts ； Lubricating friction pair ； Prevent damage caused by vacuuming. 12. Why does the backup pump need to be cranked regularly? Regular turning has three functions:: Prevent scale from getting stuck in the pump ； Prevent pump shaft deformation ； Turning the car can also bring lubricating oil to various lubrication points to prevent the shaft from rusting. The bearings are lubricated, which is helpful for driving immediately in an emergency. 16. What are the causes of abnormal heating of centrifugal pumps during operation? Heating is a manifestation of the conversion of mechanical energy into thermal energy. Common causes of abnormal heating of the pump include:: Heating accompanied by noise is usually caused by damage to the bearing ball spacer. The bearing sleeve in the bearing box is loose, and the front and rear glands are loose, causing heat due to friction. The bearing hole is too large, causing the bearing outer ring to loosen. There is foreign matter in the pump body. The rotor vibrates greatly, causing the sealing ring to wear. The pump is empty or the pump is overloaded. The rotor is unbalanced. Too much or too little lubricating oil and substandard oil quality. 17. What are the causes of centrifugal pump vibration? The rotor is unbalanced. The pump shaft and motor are misaligned, and the wheel rubber rings are aging. Excessive wear of bearings or sealing rings causes rotor eccentricity. The pump is empty or there is gas in the pump. The suction pressure is too low, causing the liquid to vaporize or nearly vaporize. The axial thrust becomes larger, causing axles to cross. Improper lubrication of bearings and packing and excessive wear. Bearings worn or damaged. The impeller is partially blocked or the external accessory pipeline is vibrating. Too much or too little lubricating oil (grease). The foundation of the pump is not rigid enough and the bolts are loose. 18. What are the standards for centrifugal pump vibration and bearing temperature? The vibration standard of centrifugal pump is: The rotation speed is less than 1500vpm and the vibration is less than 0.09mm. The rotation speed is 1500~3000vpm, and the vibration is less than 0.06mm. The bearing temperature standard is: Sliding bearings are less than 65℃, rolling bearings are less than 70℃. 19. When the pump is running normally, how high should the cooling water be? When the pump is operating normally, the cooling water opening size is most suitable when the drainage temperature is about 40°C. At this time, the discharge water is a little warm when touched by hand, and the cooling effect is best. In particular, the cooling water of the end face seal cannot be opened too large in winter to prevent the sealing rings of the dynamic and static rings from hardening due to low water temperature and losing elasticity, causing the seal to fail. 20. What happens when the centrifugal pump is evacuated? When the running pump starts to evacuate, it will suddenly make noise and vibration, accompanied by a decrease in pressure, flow rate and current. When the evacuation is serious, the pump will vibrate strongly, the pressure will return to zero, and no liquid will be pumped out of the pump. 21. What are the causes of bearing box heating? The pump shaft and motor shaft are not concentric. There is too much or too little lubricating oil (grease), and the oil (grease) deteriorates. The oil ring is broken or jumps out of its fixed position. The axial thrust increases. Insufficient or interrupted cooling water. Bearing wear. The flow rate is too small, causing the pump to be close to emptying. Pump vibration caused by weak foundation, unbalanced rotor, loose bolts, etc. 22. Why does the pump need to be antifreeze in winter? Water expands in volume below zero. If the water left in the pump body is not cleaned out, the force generated by the volume expansion at low temperatures will cause the pump body to swell and crack, causing unnecessary damage. The main methods of antifreeze are as follows:: Drain the water from the idle pump. Keep the cooling water flowing slowly and steadily. Insulate the pump or use steam or hot water to heat it. Backup pumps keep the inlets and outlets open. 23. What to do if the pump freezes? After the pump is frozen, it must not be blown directly with steam to prevent the pump from rupturing due to uneven thermal expansion. After the pump is frozen, first pour it with cold water, and then after the car is turned on, you can pour it with steam or hot water. 24. Why does the pump body need to be cooled? When the pump is running, the flow friction between the liquid and the pump body will cause friction between the rotating part and the fixed part such as the balls and inner and outer rings of the bearing, the bushing and the packing. The friction will generate heat. At the same time, the high medium temperature is transmitted to the pump, causing the pump body to heat up. The purpose of cooling is to reduce the temperature of the pump body, pump seat, bearing box, and shaft seal, and prevent these parts from deformation, aging and damage due to temperature rise. 25. Under what circumstances does the motor need to stop in an emergency? When personal safety is endangered. When the motor emits smoke or smells, or catches fire. When large vibration or axial movement occurs. When the fuselage or bearings heat to the extreme. The motor rotates slowly and makes abnormal sounds. 26. Explain the models of domestic centrifugal oil pumps. For example, what does 100YII--100×2A mean? 100--Pump suction inlet diameter Y--Single-stage centrifugal pump II--Pump material code, the second type of carbon steel is not resistant to corrosion temperature 200~400℃ A--The first turning of the impeller outer diameter 27. How to identify cavitation phenomenon? 1. There is a loud noise in the pump. 2. The outlet pressure is unstable and cannot be measured in severe cases. 3. Pump body vibrates. 4. Medium temperature rises