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1. What is the main working principle of a centrifugal pump? The electric motor drives the impeller to rotate at high speed, generating centrifugal force. Due to this centrifugal force, the liquid is forced into the side channels and discharged from the pump, or it enters the next stage of impellers. This reduces the pressure at the inlet of the impeller, creating a pressure difference with the pressure acting on the liquid being drawn in. This pressure difference drives the liquid into the pump, and as the centrifugal pump continues to rotate, liquid is continuously drawn in and discharged. 2. What are the functions of lubricating oils (greases)? Lubrication and cooling, flushing, sealing, vibration damping, protection, and load relief. 3. Through which three levels of filtration must lubricating oil pass before use? Level 1: Between the original lubricant container and the fixed container ； Level 2: Fixing between the oil barrel and the oil jug ； Level 3: Between the oil can and the refueling point. 4. What are the “five fixed principles” for equipment lubrication? Fixed location: Refuel at the designated location as specified ； Timing: Lubricate the relevant areas at specified intervals and change the oil regularly ； Quantitative: Refuel according to the consumption amount ； Qualification: Select appropriate lubricants based on different machine models, and ensure that the quality of the lubricants is satisfactory ； Designated person: Each fueling station must have a designated person in charge. 5. What are the hazards of water in the lubricating oil of mechanical pumps? Moisture can reduce the viscosity of lubricating oil, weaken the strength of the oil film, and diminish the lubrication effect. Water freezes below 0°C, which severely affects the low-temperature fluidity of lubricating oil. Moisture can accelerate the oxidation of lubricating oil and promote the corrosion of metals by low-molecular-weight organic acids. Moisture increases the foaming tendency of lubricating oil, making it prone to forming foam. Moisture can cause metal parts to rust. 6. What are the maintenance tasks for pumps? Strictly implement the post responsibility system as well as rules and regulations regarding equipment maintenance. Equipment lubrication follows the \"five fixations\" and \"three-stage filtration\" principles, with lubrication equipment that is complete and clean. Maintenance tools, safety equipment, fire-fighting devices, etc. are all complete and in good condition, and are neatly arranged. 7. What are the standards for common shaft seal leaks? Packing seal: For light oils, less than 20 drops per minute; for heavy oils, less than 10 drops per minute. Mechanical seal: For light oils, less than 10 drops per minute; for heavy oils, less than 5 drops per minute. 10. Why cannot a centrifugal pump be started when its impeller does not rotate? If the centrifugal pump will not rotate, it indicates that there is a fault inside the pump; this fault could be caused by the impeller being stuck, the pump shaft being bent too much, the moving and stationary parts of the pump having rusted together, or excessive pressure inside the pump. If the pump is forced to start without the pump disc rotating, the powerful torque of the motor will cause the pump shaft to spin forcefully, leading to damage to the internal components such as a broken or twisted pump shaft, a damaged impeller, burned-out motor coils, and it may also cause the motor to trip, resulting in a failed start. 11. What is the function of sealing oil? Cooling sealing parts ； Lubricated friction pair ； Prevent vacuum-induced damage. 12. Why is it necessary to regularly turn the standby pump manually? Regular turning of the pump serves three purposes: to prevent scaling and jamming inside the pump ； Prevent pump shaft deformation ； The turning gear can also deliver lubricating oil to various lubrication points, preventing the shafts from rusting; lubricated bearings facilitate immediate startup in emergency situations. 13. What are the reasons for abnormal overheating in a centrifugal pump during operation? Heat generation is a manifestation of mechanical energy being converted into thermal energy. Common causes of abnormal heating in pumps include heat generation accompanied by noise, which is usually due to damage to the bearing ball spacers. The bearing retainers in the bearing housing are loose, as are the front and rear gland covers; friction causes heating. The bearing hole is too large, causing the outer ring of the bearing to become loose. There is a foreign object inside the pump. Severe rotor vibration causes wear of the sealing ring. The pump is under vacuum or the load on the pump is too high. Rotor imbalance. Too much or too little lubricating oil, as well as substandard oil quality. 14. What are the causes of vibration in centrifugal pumps? Rotor imbalance. The pump shaft is out of alignment with the motor, and the rubber gaskets on the coupling are worn out. Excessive wear of the bearings or sealing rings causes the rotor to become eccentric. The pump is evacuated or there is gas inside the pump. The suction pressure is too low, causing the liquid to vaporize or nearly vaporize. The axial thrust increases, causing shaft misalignment. The bearings and packing are inadequately lubricated, resulting in excessive wear. The bearing is worn or damaged. Local blockage of the impeller or vibration in external connecting pipelines. Too much or too little lubricating oil (grease). The stiffness of the pump foundation is insufficient, and the bolts are loose. 15. What are the standards for centrifugal pump vibration and bearing temperature? The vibration standard for centrifugal pumps is: a rotational speed of less than 1500 vpm, with vibrations of less than 0.09 mm. Rotation speed: 1500–3000 vpm, vibration: less than 0.06 mm. The standard bearing temperature is: less than 65°C for sliding bearings, and less than 70°C for rolling bearings. 16. What should be the appropriate flow rate of cooling water when the pump is operating normally? When the pump is operating normally, the flow rate of the cooling water should be set so that the discharge temperature remains around 40°C. At this time, the water discharged is slightly warm to the touch, providing the best cooling effect. In particular, the cooling water flow for end-face sealing should not be set too high in winter, to prevent the sealing rings of the moving and stationary rings from hardening due to low water temperatures, thereby losing their elasticity and causing the seal to fail. 17. What are the symptoms when a centrifugal pump is under vacuum? When a pump in operation begins to lose vacuum, it suddenly emits noise and vibration, accompanied by a decrease in pressure and flow rate as well as a reduction in current. When the vacuum level becomes severe, the pump experiences intense vibration, the pressure drops to zero, and no liquid is discharged from the pump. 18. What are the reasons for the heating of the bearing housing? The pump shaft is not aligned with the motor shaft. Too much or too little lubricating oil (grease), or the oil (grease) has deteriorated. The oil ring is broken or has jumped out of its fixed position. The axial thrust increases. Insufficient or interrupted cooling water. Bearing wear. The flow rate is too low, causing the pump to be nearly emptied. Vibration of the pump caused by reasons such as a weak foundation, unbalanced rotor, and loose bolts. 19. Why is it necessary to protect pumps from freezing in winter? Water expands in volume when the temperature drops below zero degrees. If the water remaining inside the pump is not removed, the force generated by this expansion at low temperatures can cause the pump to crack, resulting in unnecessary damage. The main methods for preventing freezing are as follows: Drain the water remaining in idle pumps. Keep the cooling water flowing continuously. Insulate the pump or use steam or hot water for heating. The backup pump maintains flow in and out. 20. What should be done if the pump freezes? Once the pump freezes, it must never be blown with steam directly, to prevent it from breaking due to uneven thermal expansion of the pump body. After the pump freezes, first pour cold water on it; once it starts moving, it can be treated with steam or hot water. 21. Why does the pump body need to be cooled? During operation, fluid flow friction occurs between the liquid and the pump body. Friction also arises between the rotating parts and the fixed parts, such as the balls in bearings along with their inner and outer rings, as well as between shaft sleeves and packing. Friction generates heat, and since the temperature of the medium is high, this heat is transferred to the pump, causing the pump body to heat up. The purpose of cooling is to reduce the temperature of the pump body, pump base, bearing housing, and shaft seals, thereby preventing these components from deforming, aging, or being damaged due to increased temperatures. 22. Under what circumstances should a motor be stopped urgently? When personal safety is at risk. When the motor is smoking or emitting an odor, or is on fire. When there is significant vibration or axial movement. When the fuselage or bearings heat up to their limit. The motor rotates slowly and makes abnormal noises. 23. 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--Code for the material used in the pump. The second type of carbon steel is not resistant to corrosion at temperatures of 200–400°C; A--Outer diameter of the impeller after the first machining step. 24. How can cavitation be detected? 1. A loud noise is heard inside the pump. 2. The outlet pressure is unstable; in severe cases, no flow can be achieved. 3. Vibration of the pump body. 4. Medium temperature rise