Water pumps belong to the category of electromechanical products, and heat will inevitably be generated during operation. The sources of heat include physical friction of the medium inside the pump body, heat generated by bearing rotation friction, heat generated by motor stator rotor resistance, and so on. It is normal for a water pump to generate heat, but when the heat generation is too large and the temperature rise is too high, the water pump may experience a decrease in lifespan or even damage.
The abnormal temperature rise of the water pump will be manifested in two places, the temperature rise of the pump head and the temperature rise of the motor. Most of the reasons for the abnormal temperature rise come from:
1. Overheating of the medium
In some systems, the water pump will transport high-temperature medium. When the medium temperature does not exceed the allowable temperature of the water pump, the temperature rise of the water pump can be effectively controlled. However, when the medium temperature exceeds the allowable temperature of the water pump, it will cause the pump head to overheat. At the same time, if the motor is a long shaft motor or a sleeve shaft motor, the medium will transfer heat to the motor rotor through the pump shaft, exacerbating the internal temperature rise of the motor and causing double overheating of the pump head and motor.
This situation can be measured by using a temperature gun to measure the surface of the pump casing.
Metal has good thermal conductivity, and the external temperature of the pump casing is relatively close to the temperature of the medium.
When it is confirmed that the medium exceeds the allowable temperature of the water pump, it is necessary to cool the medium to avoid high temperature damage to the water pump. Components of the water pump that are easily damaged by high temperature medium include mechanical seals, motors, etc.
2. Small traffic operation
When the water pump is put into use, if the outlet valve is kept open for a long time and the water pump is always running at a low flow rate, or if the outlet valve has been closed but there is no control circuit to shut down the water pump, resulting in the water pump running continuously, these two situations are called "pump blockage".
When operating at low flow rates, the medium inside the pump body is repeatedly rubbed and heated by the impeller. When the amount of water flowing out of the pump body is very small, the heat carried away is also very small, and more heat is retained inside the pump body, resulting in continuous temperature rise of the pump body. Eventually, the temperature becomes too high, and the medium vaporizes, causing dry wear of the mechanical seal or high temperature damage to the pump casing casting, resulting in damage to the pump.
Timely detection of abnormalities in low flow operation, opening the outlet valve to increase the water pump's outlet flow rate, can quickly reduce the pump casing temperature and enable the pump to operate normally.
For small flow operations within the plan, please use frequency conversion to control the water pump or add a return pipe to protect the water pump.
3. Mechanical friction
The mechanical friction mentioned here does not refer to the friction in the bearing area, but to the abnormal friction that occurs inside the water pump, such as particle impurities entering the pump casing, grinding in the gap between the mouth ring, or welding waste from pipelines entering the pump body, causing friction between the impeller cover plate and the pump casing.
This type of friction may not generate high heat on its own and will not cause significant temperature rise inside the pump casing. However, for low-power water pumps, it may increase the resistance to pump operation, cause motor overload, and ultimately result in abnormal motor temperature rise.
The friction caused by foreign objects entering requires disassembling the water pump to clean the foreign objects, and replacement is needed for parts that have been damaged by friction.
For this point, it can be seen that the maintenance of the water pump is a comprehensive analysis of the cause of the problem, rather than just treating the head and feet.
4. Low voltage
In some remote areas or places with unstable power grid voltage, it may be possible for the water pump to be connected to a voltage lower than the motor limit. Generally speaking, the single-phase power supply is 220V, and the three-phase power supply is 380V. According to the motor's I standard, the motor can operate continuously within ± 5% deviation of the rated voltage. If the voltage drops beyond this ratio, it will cause excessive internal current in the motor, resulting in an increase in the temperature rise of the stator and rotor resistance, ultimately manifested as abnormal temperature rise of the motor.
In this situation, a multimeter can be used to measure the phase line voltage. When the voltage is below the allowable value, the grid voltage needs to be adjusted
5. Wiring error
Wiring error refers to the use of incorrect star angle connections in the wiring of a three-phase motor, which often results in abnormal temperature rise of the motor due to the connection of star voltage to the angle connection, causing an increase in phase to phase voltage and operating current, leading to abnormal temperature rise of the motor and ultimately damaging the motor.
The nameplate or wire box cover of most motors will indicate the corresponding voltage wiring method, and it is necessary to verify the power supply voltage and use the correct star angle connection.
6. Poor heat dissipation
There are many reasons for poor heat dissipation, and the common reasons can be roughly summarized as:
(1) The ambient temperature is too high. Due to the installation of the water pump inside a sealed box, the air temperature inside the box rapidly increases under direct sunlight in summer. When the temperature of the working environment of the water pump exceeds the allowable temperature of the motor, the cooling effect of the motor fan of the water pump begins to decrease, making it difficult for the heat generated by the normally running motor to be dissipated in a timely manner, resulting in motor overheating during long-term operation.
(2) The motor fan cover window is obstructed. When the rear of the motor is close to obstacles or outdoor plastic bags are attached to the fan cover window, the fan cannot provide effective ventilation to blow the motor cooling ribs, causing continuous temperature rise and overheating of the motor.
(3) The motor fan cover is missing, and the cooling fan, like a water pump impeller, requires a certain flow channel to provide ventilation. The fan cover is the "pump casing" of the fan, and the centrifugal fan blades require the presence of the fan cover to generate axial airflow. When the fan cover is missing, the fan loses the ability to blow the motor cooling ribs, causing the motor to overheat.
(4) The motor heat dissipation ribs are covered with oil stains. When the water pump operates in a poor environment and oil stains exist, the oil stains will adhere to the surface of the motor heat dissipation ribs. Due to the characteristics of oil, it will block the external heat exchange of the heat dissipation ribs. Under normal air flow blowing, the heat dissipation ability of the heat dissipation ribs is greatly reduced, which can also cause the motor to overheat.
7. Overload of water pump
For single-stage impeller water pumps, the shaft power curve is usually a single increase, and the higher the flow rate, the greater the power. Therefore, when selecting the operating point, the corresponding motor can only ensure normal operation to the left of this operating point. When the system gate is too wide open and the resistance is too low, the operating point of the water pump shifts to the right, causing the shaft power to increase. The increased shaft power may exceed the rated power of the motor, resulting in the problem of the motor pulling a large vehicle with a small horse.
If the motor overload is caused by a deviation from the operating point, the system valve opening should be adjusted to place the system resistance curve to the left of the design operating point.
8. Frequent start stop of the motor
The current at the moment of starting for motor products is relatively high, and motors operating at power frequency can even reach 6-7 times the rated current at the moment of starting. Excessive current can exacerbate the temperature rise of the motor in a short period of time. If frequent starting occurs, the temperature rise of the motor will quickly increase.
There are generally two reasons for frequent motor start stop:
(1) Pressure setting issue: When the system sets the pressure incorrectly, it may cause the pump to stop. The inlet water pressure is lower than the starting pressure of the water pump, and the water pump needs to be started. However, after the water pump is started, due to the small actual water consumption, the head of the water pump and the pressure of the inlet pipe network quickly exceed the stopping pressure, causing the water pump to immediately stop, resulting in a start stop stop problem.
(2) System leakage problem: When there is leakage in the system, even if no one is using water, the pressure at the outlet of the water pump will continue to drop, causing the water pump to start periodically. When the pressure relief rate is fast, the water pump will start more frequently.
The above are the manifestations of abnormal temperature rise, hoping to be helpful to everyone.
