Question: Why is the centrifugal pump not getting water?

Update: 14-12-2019

There are many reasons why the centrifugal pump does no […]

There are many reasons why the centrifugal pump does not get water, sometimes it is caused by a single reason, sometimes it is caused by multiple reasons. First of all, simple faults should be eliminated, then the problems should be judged one by one and analyzed in depth, and then the faults should be eliminated and solved fundamentally.
The main reasons for the failure of the centrifugal pump to feed water are: the pump body and the suction pipe are not exhausted; the suction pipe is broken or the pump casing is not well sealed and the air intake; the speed of the pump is too low; the suction stroke is too high; Causes such as blocked foot valve.
Reason one: the water is not filled or the air in the inlet pipe is not pumped; the centrifugal pump does not produce water;
Solution: Continue irrigation or clean the air in the inlet pipe.
Centrifugal pump is not filled with water before starting the pump should be filled with water, *** to exclude air in the pump body and suction pipe. Before filling the water, open the air screw, then add water until the water leaks out from the air vent, and then turn the pump shaft a few times. If the water continues to flow, it indicates that the water is full, then tighten the exhaust screw and prepare to start. However, in actual operation, most operators are not filled with sufficient water before the pump is started.Sometimes, although water is seen to overflow from the vent hole, the pump shaft is not turned to allow the air to be completely discharged. There is still air in the impeller. When the pump is running, Air enters the pump casing and affects the pumping capacity.
The water inlet pipe should be horizontal or slightly higher near the water pump. Be sure to keep the water inlet of the water pump high. Otherwise, the air cannot be discharged in a high place.
的 The horizontal section of the suction pipe that is in contact with the pump has a downward slope of more than 0.5% in the direction of the reverse flow. The end connected to the water inlet of the pump is the higher point, and it should not be completely horizontal. If it is tilted upward, air will remain in the water inlet pipe, which reduces the vacuum in the water pipe and the pump and affects the water absorption. In this case, the water suction pipe needs to be reinstalled.
Reason two: The lift required by the actual working conditions is too high, and the lift of the centrifugal pump is too low to meet the requirements of the working conditions;
Solution: Replace the pump with higher head.
Theoretically, at an atmospheric pressure, the suction stroke should be 10.34 m. In terms of sea level elevation, the average user area must exceed sea level elevation, so the suction height must be less than 10.34 m. On the other hand, the vacuum that a water pump cannot form, and the greater the degree of vacuum, the more likely it is to cause gasification of the water and cause cavitation, which is not conducive to the operation of the pump, so the allowable suction lift of the pump nameplate is between 3.50 ~ 8.20 m. Also included is the loss of water head in the suction pipe. In this case, it is necessary to recalculate the working suction. The working suction must be smaller than the rated suction of the nameplate. Many people usually use the height difference between the water surface of the front pond and the center line of the pump as the working suction stroke. However, in actual operation, the water surface of the front pond always fluctuates, so a certain margin must be reserved.
Cause three: The air leakage in the suction pipe or sealing device is serious;
Solution: block or repair the leaking part, and compress or replace the seal.
Cause of centrifugal pump not water Once the suction pipe is damaged or the pump casing is not well sealed, air will enter the pump body, which will cause the pump to fail to pump water. Due to the long-term potential underwater of the suction pipe, holes appear in the pipe wall corrosion, and the water surface continuously drops after the pump works. When these holes emerge from the water surface, air enters the suction pipe from the hole. In this case, the suction pipe must be replaced or repaired.
Because the pump shaft is rotating and the pump casing is stationary, there must be a certain gap at the contact between the shaft and the pump casing.To prevent high-pressure liquid in the pump from leaking along the gap, or to prevent outside air from entering the pump from the opposite direction, a shaft sealing device must be provided. The shaft seal device of the centrifugal pump is commonly a stuffing box shaft seal, which is filled with soft packing. The packing of the pump has been worn or too loose due to long-term use, causing a large amount of water to be ejected from the gaps between the packing and the pump shaft bushing, so that external air enters the interior of the pump from these gaps.The treatment method for this situation is Replace the packing.
Cause four, when the on-site installation of the pipeline centrifugal pump is reversed, or the motor is connected incorrectly, the rotation direction of the pump is incorrect;
Solution: Reverse the motor wiring in the direction of import and export. Change any two wires to change the direction of rotation.
Reason five: the speed of the pump is too low; the centrifugal pump does not produce water;
Solution: Increase the speed of the pump.
扬 When the speed of the pump is too low, the head will decrease and the flow rate will decrease. There are many reasons for the low speed of the pump, mainly due to the following reasons.
2.3.1 Human factors A considerable part of the operators are randomly equipped with a motor because of the damage of the original motor. If the speed and power of the new motor is lower than the original motor, the speed will be reduced and the pump will not be able to lift water.
2.3.2 Mechanical failure of the pump itself Loose fastening nuts of the impeller and the pump shaft or deformation and bending of the pump shaft cause the impeller to move more, directly rub against the pump body, or damage the bearings, which may reduce the speed of the pump. If this happens, it is easy to judge from the sound and vibration of the pump when the pump is running.
2.3.3 Low voltage Some pumping stations do not have a separate transformer, but instead use the existing transformer to set up a low-voltage line to supply power. The low-voltage line is longer and the voltage reduction is large, resulting in a low voltage, which causes the motor speed to drop and cannot be normally operated. water.
Cause six: The bottom valve is rusted, and the water inlet or the channel of the impeller is blocked;
Solution: Repair the bottom valve, remove the sundries, and add a pollution barrier at the water inlet.
Cause of centrifugal pump not getting water The blocked bottom valve will also cause the pump not getting water. Among the components of the centrifugal pump, the bottom valve is a simple device, but its operation must be flexible and reliable. It is required to be closed in time when the pump is filled with water and opened in time when it is sucked. The pump has been out of service for too long, the rubber ring of the foot valve is stuck, and those without the rubber ring may rust and cause the foot valve to fail to open. The operator can find out whether the foot valve is flexible to open by hand. If the foot valve cannot be opened normally, the foot valve needs to be replaced. In addition, the bottom valve filter screen is blocked or the bottom valve sneaks into the sludge, causing the filter screen to become clogged. The operator should often clean the debris around the bottom valve. The bottom valve should be kept a certain distance from the bottom of the tank, and the submerged depth should not be less than 0.50 m.
Reason seven: The inlet pipeline is too long and the suction stroke is too large;
Solution: Reduce the installation height of the pump, or reduce the elbow valves on the suction pipe, and shorten the length of the pipeline.
Sometimes, although the working head is not high, but because the pipeline is too long and the loss along the way is large, it is still not possible to raise water or the amount of water is small. There are many bends in the pipeline, and the bends are not smooth, and local water head loss in the pipeline is large. In addition, changing the diameter of the pipeline at will will increase the head loss of the pipeline significantly. The selection of pipe diameter should be based on the economic flow rate. The pipe diameter is too large and the initial investment is large; the pipe diameter is too small, the pipeline loss is large, and the operating cost becomes high.
Reason eight: The impeller is seriously damaged, and the clearance of the leakage reducing ring is worn;
Solution: Replace the impeller and leakage reducing ring.