How To Determine And Handle Faults in Water Pumps During Operation
Nov 16, 2024
During the operation of the water pump, some abnormal phenomena may occur at any time, and these abnormal phenomena are often a precursor to equipment failure. How to diagnose faults, we can detect and correctly diagnose and handle faults in a timely manner through some abnormal phenomena during operation, minimize losses, and ensure that the equipment operates in a healthy state.
Through years of work observation and accumulation, the following three basic methods are summarized.
1, Direct analysis method
The direct analysis method is to determine the location of the water pump fault based on the intuitive phenomena of the fault, such as:
If the pointer of the pressure gauge at the outlet of the water pump reaches the end and the pressure gauge is confirmed to be normal, it can be judged that the outlet valve of the water pump has been forgotten to open or the electrical circuit of the outlet valve has poor contact, causing the valve to fail to operate. The valve should be opened or the electrical circuit should be repaired.
If there is excessive water leakage at the pump shaft core, it indicates that there is excessive wear on the inner packing of the packing cover or that the gland is too loose, and the packing cover should be replaced or tightened.
When a new pump is put into operation, if the current of the water pump motor is too high, it is often due to the packing gland being too tight, and the tightening nut should be adjusted appropriately.
If there is smoke or burnt smell from the water pump motor, the motor must have been burned out and should be replaced.
If there is columnar water spraying inside the tail cover of the water pump, it is mostly due to poor casting quality and perforation, and the casting should be replaced.
If a copper or iron listening rod is used to touch the pump bearing and a metal scraping or whistling sound is heard, the bearing at that location will fail and needs to be replaced immediately.
This type of fault can be directly diagnosed through listening, seeing, touching, and smelling methods, but most faults often present one or several indirect and implicit phenomena in the early stages, which cannot be accurately diagnosed at a glance. Therefore, in addition to requiring operators to master and be proficient in direct fault diagnosis methods, they also need to gradually understand, learn, and become familiar with indirect analysis methods.
2, Indirect analysis method
Indirect analysis is a method based on professional knowledge of water pumps, using logical reasoning to analyze and determine the fault point and cause.
(1) Decreased circulating water volume
When the circulating water volume decreases, the direct analysis method can be used to determine the pump system failure. As for which part of the pump system it is, further analysis and inspection should be carried out. Therefore, when the circulating water volume decreases, the equipment condition should be checked immediately. If the valve core is seen to open very low, it can be concluded that the valve is not open due to operational errors or electrical faults. The valve should be opened or the electrical system should be repaired accordingly. If the valve core is seen to open very high, it can be concluded that the valve or valve plate has fallen off. The water pump should be stopped immediately, and then the valve core should be repaired or replaced; If the pipeline is covered with debris at the entrance, it is a blockage fault and the debris should be removed; If the valve opening of a newly invested water pump is normal but the flow rate is low, it is often due to excessive, rapid, or high resistance bends that affect the flow rate, and the pipe system bends should be simplified; If the motor speed measured with a speedometer is significantly lower than the nameplate value, it is a fault in the motor or electrical part, rather than the pump body itself.
(2) Pump vibration
The judgment process can be abbreviated as:
If the water pump vibrates during operation, the pump body and motor should be checked immediately. If the pump body and motor shaft are not concentric, improper installation may occur; → Safety maintenance issues with loose foundation screws of the water pump; → The end face of the pump and motor coupling is not parallel → Installation defect; → There is a gap between the pump and the motor coupling → Poor assembly quality; → Severe wear of bearings at the end of the pump or motor or running out of casing → Poor lubrication or poor bearing quality; Bearing bending, manufacturing defects, and poor assembly after major repairs leading to tile burning.
(3) Excessive power consumption and current of the water pump
The judgment process can be abbreviated as:
Water pump power consumption and high current - check the pump bucket, check the packing gland, and ensure that the packing is pressed too tightly; → Check the mechanical friction situation - there is friction between the rotor and the fixed part or between the balance disk and the balance ring.
3, Comprehensive analysis method
The comprehensive analysis method is an organic combination of the direct and indirect methods mentioned above, and is a basic method for analyzing and judging fault phenomena. It is mainly used for analyzing and judging complex fault phenomena. The following examples can provide a preliminary understanding and mastery of this method.
One of the faults:
The long-term operation of the water pump results in low flow rate, low outlet pressure, and overheating of the pump body and motor casing.
At this point, the following parts should be checked and judged:
1. Check if the inlet valve of the pump fails to open or if the valve stem is broken and the valve disc is detached.
2. Check for debris blockage, scaling, and corrosion in the inlet pipe of the water pump.
3. Does the gap between the impeller and the sealing ring increase due to friction.
Fault 2:
After the water pump is started, the current of the motor remains too high, causing strong vibration and abnormal noise when the water pump rotates. There is a burnt smell and white smoke at the shaft seal, and there is almost no idle time after shutdown, resulting in rapid stopping.
Reason analysis:
When the water pump starts, white smoke appears at the shaft seal and there is high rotational resistance. The main reason is that there is no water film layer established between the packing and the shaft sleeve, causing the packing to lose lubrication and cooling. This is often due to the tightness of the disc root pressure during the installation of new packing. When the water pump is started, there is no gap between the packing and the shaft sleeve for a while, and normal water discharge occurs. Due to dry friction, the surface temperature of the two increases sharply, causing overheating and high rotational resistance. As a result, the current does not turn back, the pump body vibrates, and phenomena such as burnt smell and white smoke are produced.
Solution: Switch to the backup pump and reinstall the packing, taking care not to press too tightly.
Fault 3:
The pressure gauge at the outlet of the water pump shows pressure, but the water pump still does not produce water.
At this point, it is necessary to check:
1. Is there an error in the direction of the water pump rotation.
2. Whether the impeller is blocked.
If a new water pump is installed, after excluding the above two reasons, it can be inferred that the pipeline resistance is too high.
Fault 4:
The bearing part is overheated, and there is no obvious abnormal noise or abnormal vibration of the pump body when listening carefully with a listening stick. The speed is normal, the cooling water is unobstructed, and there is molybdenum disulfide in the oil cup.
Analysis: There is no abnormal noise inside the bearing and no vibration in the pump body, indicating that the bearing is operating effectively and has not been damaged. Although there is molybdenum disulfide in the oil cup, it cannot be determined whether the oil has entered the bearing, because only poor lubrication can cause the bearing temperature to rise, so it can be inferred as an initial oil shortage fault. After inserting an iron rod into the oil cup, it can be seen that the lower part of the cup is empty, indicating a false "bridging" phenomenon of full oil.
Solution: Add lubricating oil again.
Similar false oil level accidents are prone to occur, and we should pay special attention to comprehensive analysis and judgment to ensure the normal operation of the water pump.