The working principle, performance characteristics and installation/maintenance precautions of the submersible pump

A submersible pump is a versatile water treatment tool with wide applications. Unlike ordinary pumps, a submersible pump integrates the motor and the pump as a single unit and operates underwater. It can be classified into well-type submersible pumps, operation surface submersible pumps, submersible sewage pumps, sand discharge submersible pumps, and mine vertical pumps, etc.
1. Working Principle and Performance Characteristics of Submersible Pumps A submersible pump is a general-purpose water lifting machinery that works underwater by directly connecting the motor and the pump. Its working principle is that the motor drives the impeller to rotate at high speed through the pump shaft. Under the action of centrifugal force, it does work on the liquid, converting mechanical energy into liquid energy. The liquid (water) is ejected from the impeller and expands outward in the diffusion chamber of the pump casing. The speed gradually slows down and the pressure gradually increases as it exits the pump outlet discharge pipe. The design of submersible pumps aims to "avoid entanglement and blockage". Some models are also equipped with tearing mechanisms or cutting devices, which can tear long fibers and band-like substances in the water and discharge them. The inherent weakness of submersible pumps is that the medium they pump is mostly soft, and the limit for the sand content in the water is 3%. When the sand content is high, it is prone to damage the seal, and if the motor gets water, the bearings, winding insulation will be damaged, leading to the motor burning out.
2. Installation and Use of Deep Well Submersible Pumps Submersible pumps generally have certain requirements for the deviation range of power supply voltage and frequency. For large-power submersible pumps, it is necessary to use reduced-voltage starting or soft starting to reduce the impact on the power grid or other electrical equipment as well as the submersible pump itself. The installation and use of submersible pumps should be based on the correct selection of the equipment according to the usage environment and attention to relevant matters.
2.1 Selection and Usage Environment of Submersible Pumps The selection of submersible pumps should be made correctly based on the working conditions. When selecting, the main factors to consider are flow rate, head, and installation method. Only when the selected head is close to the actual required head can the pump operate efficiently and energy-savingly. Inappropriate selection will have a significant impact on the operation of the pump.
Generally, the usage environment of deep well submersible pumps should meet the following requirements:
(1) The power supply frequency is 50Hz, and the rated voltage has an allowable deviation of ±5% of three-phase AC power supply;
(2) The solid matter content (by mass) is no more than 0.01%;
(3) The water inlet of the pump must be below the water level by 1m, but the submersible depth should not exceed 70m below the static water level, and the distance from the bottom of the well to the pump lower end should be at least 1m;
(4) The well should be vertical, the well wall should be smooth, and the well pipe should not be misaligned. 2.2 Installation of Deep Well Submersible Pumps The installation of deep well submersible pumps should first check whether the power supply lines, grid voltage, frequency, and control switches meet the usage conditions; then the pump must have good grounding measures; check whether the installation of the electrical control cabinet is correct and well grounded;
Check the lifting facilities to be safe and reliable. The installation of the submersible pump should be carried out in the following order:
(1) Remove the filter screen located in the middle of the pump, unscrew the water injection screw and water discharge screw, fill the machine with clean neutral water, and then tighten the screws. Check whether there is leakage at each connection part of the motor, and if there is leakage, perform sealing treatment.
(2) Use a 500-volt megohmmeter to measure the insulation resistance of the motor to be no less than 150 megohms, and use a screwdriver to turn the impeller to check if it rotates freely without any jamming phenomenon.
(3) First connect the short water pipe to the check valve body, install a pair of clamps on the upper flange of the short water pipe, then gently lift the pump and place it in the well, so that the clamp seat rests on the well cover.
(4) Use another pair of clamps to clamp the long water pipe and lift it to connect with the short water pipe, then remove the pair of clamps and lift another long water pipe, repeat this process for installation until completed. Then cover the well cover and fix the clamps on the well cover, and install the bent water pipe, valve, and outlet pipe of the deep well submersible pump.
(5) During the installation process, pad the two flanges of the pipe between the two flanges with pipe rubber pads, tighten the bolts symmetrically, and tie the cable to the groove on the flange of the water pipe. Do not use the cable as a lifting rope, and do not touch the cable wire. After the installation is completed, install the bent water pipe, valve, and outlet pipe. Deep well submersible pump.
(6) During the installation and operation of the deep well submersible pump, the following points should be noted:
(1) During lifting, pay attention to protecting the cable to prevent damage. The lifting device (such as tripod, hoist, or electric hoist) should have a lifting capacity greater than the weight of the submersible pump and leave sufficient margin. Before lowering, manually rotate the impeller to check if it rotates flexibly, whether the main contactor contacts are in good contact, whether there are any cracks or scratches on the cable wire and cable connector, whether the grounding of the motor shell is reliable, and use a multimeter to check the conduction of the three-phase lines. (2) When starting the submersible pump, it should be stable, without vibration and abnormal noise. Observe whether the motor operating current and line voltage have any significant fluctuations before and after starting. Pay attention to the first installation or after maintenance of the submersible pump, the test run can only be started locally to observe. If the submersible pump is abnormal, stop immediately, check if the rotation direction is correct, if the installation is proper, and find the cause to eliminate the fault before running.
3. Analysis of Common Fault Causes of Deep Well Submersible Pumps The common faults of deep well submersible pumps during use include the following six situations: (1) Unable to pump water or insufficient head: At this time, the pump does not rotate when it is turned on, and the submersible pump makes a loud noise when it is idling. This phenomenon is mostly caused by the damage of the bearings of the submersible pump.
(2) Poor sealing: There is a double-end face mechanical seal component at the shaft extension end of the pump motor. It is made of high wear-resistant materials. After the submersible pump is used for a period of time, the sealing component becomes ineffective due to wear or natural aging, causing oil leakage and water seepage. Additionally, there are circular rubber sealing rings on each mechanical mating surface to form a sealing pad to prevent water from entering the pump body. However, due to the high rotational speed of the motor used in the submersible pump, severe wear of the mechanical seal end face is inevitable during long-term use.
(3) Broken outlet pipe and leakage: One can hear the normal rotation sound of the pump wheel hanging in the deep well (the electric meter also rotates normally), but no water is pumped or only a small amount of water comes up. This situation is mostly caused by the damage of the water outlet pipe.
(4) Stuck pump: The pump does not rotate, but a buzzing sound can be heard. This is mostly caused by foreign objects blocking the pump impeller. For example, due to geological reasons in our school, the water quality of the well contains a large amount of sand, which easily causes damage to the filter screen cover.
(5) Electric leakage: Electric leakage is one of the common faults of the pump. The fault phenomenon is that when the switch is closed, the leakage protector in the power distribution room automatically trips. This is because water enters the pump body, causing the motor winding to leak electricity.
(6) Failure of starting capacitor: When power is connected, a buzzing sound can be heard, but the submersible pump does not rotate; if the impeller is gently moved, the submersible pump can immediately rotate, which can be judged as the capacitor being damaged.