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21 key points about centrifugal pump you need to know (2)
11. What are the causes of abnormal heating of the centrifugal pump in operation?
Common causes of abnormal heating of the pump are: heat with noise, usually the bearing ball isolation frame is damaged. The bearing retainer in the bearing box is loose, the front and rear gland are loose, and the heat is caused by friction. The bearing hole is too large, causing the outer ring of the bearing to loosen. There are foreign objects in the pump. The rotor vibrates too much, causing the seal ring to wear out. The pump is evacuated or the load of the pump is too large. The rotor is unbalanced. Too much or too little lubricating oil and unqualified oil.

12. What are the causes of centrifugal pump vibration?
The rotor is unbalanced. The pump shaft and the motor are misaligned, and the apron of the wheel is aging. The bearing or seal ring wears too much, resulting in rotor eccentricity. The pump is evacuated 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 a string of shafts. Bearings and packing are improperly lubricated and excessively worn. The bearing is worn or damaged. The impeller is partially blocked or the external auxiliary pipeline vibrates. Too much or too little lubricating oil (grease). The rigidity of the foundation of the pump is not enough, and the bolts are loose.

13. What is the standard of centrifugal pump vibration and bearing temperature?
The vibration standard of the centrifugal pump is: speed is less than 1500vpm, vibration is less than 0.09mm. The rotation speed is 1500 ~ 3000vpm, and the vibration is less than 0.06mm.
Bearing temperature standards are: sliding bearings less than 65 ℃, rolling bearings less than 70 ℃.

14. When the pump is running normally, how many temperature is proper for the cooling water?
When the pump is in normal operation, the cooling water opening size is most suitable for the drainage temperature of about 40 ℃. At this time, the temperature of the discharged water is touched by hand, and the cooling effect is the best. In particular, the cooling water sealed at the end face cannot be opened too much in winter to prevent the dynamic and static ring seals from hardening due to low water temperature, and the loss of elasticity makes the seal invalid. 
15. What happens when the centrifugal pump is evacuated?
When the pump in operation starts to evacuate, it will suddenly emit noise and vibration, accompanied by a reduction in pressure, flow and current. When the pumping is serious, the pump will vibrate strongly, the pressure will return to zero, and no liquid will be ejected from the pump.

16. What are the reasons for the heating of the bearing box?
The pump shaft is not concentric with the motor shaft. There is too much or too little lubricating oil (fat), and the oil (fat) deteriorates. The oil ring breaks or jumps out of a fixed position. The axial thrust increases. The cooling water is insufficient or interrupted. Bearing wear. The flow rate is too small, so that the pump is nearly evacuated. The vibration of the pump caused by weak foundation, unbalanced rotor, loose bolts and other reasons.

17. Why should the pump prevent freezing in winter?
The volume expansion of water occurs below zero. If the water left in the pump body is not cleaned out, the force generated by the volume expansion at low temperature will cause the pump body to burst and cause unnecessary damage. There are mainly the following methods of antifreeze: Drain the water stored in the idle pump. Maintain a long stream of cooling water. Insulation of the pump or heat tracing with steam and hot water. The standby pump keeps the inlet and outlet in circulation.

18. How to deal with the pump after freezing?
After the pump is frozen, it should never be blown directly with steam to prevent it from bursting due to uneven thermal expansion of the pump body. After the pump is frozen, pour it in cold water first, and then use the steam or hot water to pour the train.
19. Why should the pump body be cooled?
During the operation of the pump, the flow friction between the liquid and the pump body, the rotating part and the fixed part such as the ball of the bearing and the inner and outer rings, the bushing and the packing will produce friction, because the friction will generate heat, and at the same time, due to the high temperature. make the pump body heat. The purpose of cooling is to reduce the temperature of the pump body, pump base, bearing box and shaft seal to prevent these parts from being deformed, aging and damaged due to temperature rise.

20. Under what circumstances should the motor stop urgently?
When personal safety is endangered. When the motor emits smoke or smells or catches fire. When there is a lot of vibration or axial series. When the fuselage or bearing heats up to the limit. The motor speed is slow and accompanied by abnormal sound.

21. How to judge the cavitation phenomenon?
There was a fierce noise in the pump. The outlet pressure is unstable and can not be measured in severe cases. The pump body vibrates. The medium temperature rises.