Must master 20 basic knowledge points of centrifugal pumps
1. What is the main working principle of a centrifugal pump?
The electric motor drives the impeller to rotate at high speed, causing the liquid to generate centrifugal force. Due to the effect of centrifugal force, the liquid is thrown into the measuring flow channel and discharged from the pump, or enters 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 is used in 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 and cooling effect, flushing effect, sealing effect, shock absorption effect, protection effect, unloading effect.
3. What are the three levels of filtration that lubricating oil needs to go through before use?
Level 1: Between the original lubricating oil drum and the fixed drum;
Level 2: Fixed between oil drum and oil pot;
Level 3: Between the oil pot and the refueling point.
4. What is the "Five Fixtures" for equipment lubrication?
Fixed point: Refuel according to the prescribed point;
Timed: Fill the lubricating oil parts with oil according to the prescribed time and change the oil regularly;
Quantitative: refuel according to the consumption quantity;
Qualitative: Select different lubricating oils according to different models and ensure that the oil quality meets the qualified standards;
Fixed person: Each refueling area must have a dedicated person in charge.
5. What are the hazards of water content in lubricating oil for pumps?
Moisture can reduce the viscosity of lubricating oil, weaken the strength of the oil film, and reduce the lubrication effect.
Water below 0 ℃ will freeze, seriously affecting the low-temperature fluidity of lubricating oil.
Water can accelerate the oxidation of lubricating oil and promote the corrosion of metals by low molecular organic acids.
Water will increase the foam property of lubricating oil and make it easy to produce foam.
Moisture can rust metal parts.
6. What are the maintenance and upkeep contents of the pump?
Seriously implement the job responsibility system and equipment maintenance rules and regulations.
The equipment lubrication achieves "five fixed" and "three-stage filtration", and the lubricator is complete and clean.
Maintenance tools, safety facilities, fire-fighting equipment, etc. are complete and in good condition, and placed neatly.
7. What are the standards for common shaft seal leaks?
Packing seal: less than 20 drops/min for light oil and less than 10 drops/min for heavy oil
Mechanical seal: less than 10 drops/min for light oil and less than 5 drops/min for heavy oil
8. Why cannot the centrifugal pump disc be started when it is not in operation?
If the centrifugal pump disc does not move, it indicates that there is a malfunction inside the pump. This malfunction may be due to the impeller getting stuck or the pump shaft bending excessively, or the dynamic and static parts of the pump rusting, or the pressure inside the pump being too high.
If the pump disc is forced to start without moving the car, the strong motor force will drive the pump shaft to move vigorously, which will cause damage to internal components, such as the pump shaft breaking, twisting, impeller breaking, motor coil burning, and may also cause the motor to trip and fail to start.
9. What is the function of sealing oil?
Cooling sealing parts: lubricating friction pairs; Prevent vacuum damage.
10. Why do backup pumps need to be regularly cranked?
There are three functions of regular turning; Prevent scaling and jamming inside the pump; Prevent pump shaft deformation; The turning gear can also bring lubricating oil to various lubrication points to prevent shaft rust. Lubrication of the bearings is beneficial for immediate driving in emergency situations.
11. What are the reasons for abnormal heating of centrifugal pumps in operation?
Heating is the manifestation of mechanical energy being converted into thermal energy, and common causes of abnormal heating in pumps include:
Heating accompanied by noise is usually caused by damage to the bearing ball isolation frame.
The bearing guard sleeve in the bearing box is loose, and the front and rear pressure covers are loose, causing heat generation due to friction.
The bearing hole is too large, causing the outer ring of the bearing to loosen.
There is a foreign object inside the pump body.
The large vibration of the rotor causes wear on the sealing ring.
The pump is empty or the pump's load is too high.
The rotor is unbalanced.
Too much or too little lubricating oil and unqualified oil quality.
12. What are the causes of centrifugal pump vibration?
The rotor is unbalanced.
The pump shaft is not aligned with the motor, and the rubber ring of the coupling wheel is aging.
Excessive wear of bearings or sealing rings can cause rotor eccentricity.
The pump is empty or there is gas inside the pump.
The suction pressure is too low, causing the liquid to vaporize or almost vaporize.
The increase in axial thrust causes shaft misalignment.
Improper lubrication and excessive wear of bearings and packing.
Wear or damage to bearings.
Local blockage of impeller or vibration of external accessory pipelines.
Excessive or insufficient lubricating oil (grease).
The foundation stiffness of the pump is insufficient, and the bolts are loose.
13. What are the vibration and bearing temperature standards for centrifugal pumps?
The vibration standard of a centrifugal pump is:
The rotational speed is less than 1500VPM, and the vibration is less than 0.09mm.
The rotational speed is 1500-3000VPM, and the vibration is less than 0.06mm.
The temperature standard for bearings is: sliding bearings are less than 65 ℃, and rolling bearings are less than 70 ℃.
14. When the pump is running normally, how much cooling water should be turned on appropriately?
When the pump is operating normally, the cooling water opening size is most suitable with a drainage temperature of around 40 ℃.
At this point, touching the discharged water with your hands may cause a slight temperature, resulting in the best cooling effect.
Especially, the cooling water for the end face seal should not be opened too much in winter to prevent the sealing rings of the dynamic and static rings from hardening due to low water temperature, losing elasticity and causing sealing failure.
15. What is the phenomenon when the centrifugal pump is empty?
When the running pump starts to empty, it will suddenly emit noise, vibration, accompanied by a decrease in pressure, flow rate, and current. When the suction is severe, the pump will experience strong vibration, the pressure will return to zero, and there will be no liquid ejected from the pump.
16. What are the reasons for the heating of the bearing box?
The pump shaft and motor shaft are not concentric.
Excessive or insufficient lubricating oil (grease) leads to deterioration of the oil (grease).
The oil ring is broken or jumps out of a fixed position.
The axial thrust increases.
Insufficient or interrupted cooling water.
Wear of bearings.
The flow rate is too small, causing the pump to approach an empty state.
Vibration of the pump caused by weak foundation, unbalanced rotor, loose bolts, and other reasons.
17. Why do pumps need to be antifreeze in winter?
Water undergoes volume expansion below zero degrees Celsius. If the water remaining in the pump body is not cleaned out, the force generated by the volume expansion at low temperatures will cause the pump body to expand and crack, causing unnecessary damage. There are several main methods for antifreeze:
Drain the stored water from the idle pump.
Keep the cooling water flowing continuously.
Insulate the pump or heat it with steam or hot water.
The standby pump maintains flow at the inlet and outlet.
18. What should be done after the pump freezes?
After the pump freezes, it should never be blown directly with steam to prevent it from cracking due to uneven thermal expansion of the pump body.
After the pump freezes, pour it with cold water first, and then wait for the engine to start. You can pour it with steam or hot water.
19. Why does the pump body need to be cooled?
The flow friction between the liquid and the pump body during the operation of the pump, as well as the slight friction between the rotating part and the fixed part such as the ball and inner and outer rings of the bearing, the shaft sleeve and packing, will generate heat due to friction. At the same time, the high temperature of the medium conducts heat to the pump body, 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, preventing deformation, aging, and damage to these parts due to temperature rise.
20. Under what circumstances does the motor need to stop urgently?
When endangering personal safety.
When the motor emits smoke, odor, or catches fire.
When significant vibration or axial displacement occurs.
When the body or bearings heat up to the limit.
The motor speed is slow and accompanied by abnormal sounds.
21. Explain the models of domestically produced centrifugal oil pumps, for example, what do 100Y II-100X2A represent?
100- Pump suction diameter Y - Single stage centrifugal pump II - Pump material code, second type carbon steel not resistant to corrosion temperature of 200-400 ℃ A - First turning of impeller outer diameter.
22. How to distinguish cavitation phenomena?
1. There is a loud noise inside the pump.
2. The export pressure is unstable, and in severe cases, the volume cannot be increased.
3. Pump body vibration.
4. The medium temperature rises.