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DMC pumps are important equipment for deep well water lifting. During operation, the entire unit is submerged in water to extract groundwater to the surface. They are used for domestic water supply, mine rescue, industrial cooling, farmland irrigation, seawater lifting, ship trim adjustment, and fountain landscapes. Hot water submersible pumps are used for hot spring bathing and are also suitable for extracting groundwater from deep wells, as well as for water lifting projects in rivers, reservoirs, and canals. They are mainly used for farmland irrigation and water supply for people and livestock in high mountain areas, and can also be used for central air conditioning cooling, heat pump units, chiller pump units, and drainage in cities, factories, railways, mines, and construction sites. The general flow rate can reach 5~650m³/h, and the head can reach 10-550 meters.

DMC pump working principle

There are several types of submersible pumps; the motor windings can be oil-immersed, water-immersed, or dry type. You must read the manual before use to avoid errors. If unused for a long period, the impeller must be rotated before use to prevent seizure and winding burnout due to prolonged inactivity. Before starting the pump, the suction pipe and the pump interior must be filled with liquid. After starting, the impeller rotates at high speed, causing the liquid inside to rotate with the blades. Under the action of centrifugal force, the liquid flies away from the impeller and is ejected outward. The velocity of the ejected liquid gradually decreases in the diffusion chamber of the pump casing, while the pressure gradually increases, and then it flows out from the pump outlet and discharge pipe. At this time, a vacuum low-pressure zone without air or liquid is formed at the center of the blades because the liquid is thrown to the periphery. Under the action of atmospheric pressure on the liquid surface, the liquid in the sump flows into the pump through the suction pipe. In this way, the liquid is continuously sucked up from the sump and continuously flows out from the discharge pipe.

DMC pump mechanical structure

The submersible electric pump unit consists of four main parts: the water pump, the submersible motor (including cable), the water delivery pipe, and the control switch. The submersible pump is a single-suction multi-stage vertical centrifugal pump. The submersible motor is a sealed water-filled wet-type vertical three-phase squirrel-cage asynchronous motor. The motor and water pump are directly connected via a claw-type or single-key sleeve coupling. It is equipped with three-core cables of different specifications. The starting equipment includes air switches and autotransformer reduced-voltage starters of different capacity ratings. The water delivery pipes are made of steel pipes of different diameters, connected using flanges. High-head electric pumps use gate valves for control. A labyrinth sand guard and two reverse-assembled skeleton oil seals are installed on the upper part of the submersible motor shaft to prevent flowing sand from entering the motor. The submersible motor uses water-lubricated bearings. The lower part is equipped with a rubber pressure-regulating diaphragm and a pressure-regulating spring, forming a pressure-regulating chamber to adjust pressure changes caused by temperature. The motor windings use polyethylene insulation and nylon-sheathed water-resistant magnet wire. The cable connection follows cable joint procedures: remove the joint insulation, scrape off the varnish layer, connect separately, solder firmly, wrap with one layer of raw rubber, then wrap with 2-3 layers of waterproof adhesive tape, and finally cover with 2-3 layers of waterproof cloth or bond a layer of rubber (bicycle inner tube) with water-resistant adhesive to prevent water ingress. Each guide shell stage of the submersible pump contains a rubber bearing. The impeller is fixed to the pump shaft with a tapered sleeve. The guide shells are connected into a single unit using threads or bolts. A check valve is installed at the upper part of high-head submersible pumps to prevent unit damage caused by water hammer during shutdown. The motor is sealed using precision spigot bolts, with rubber gaskets added at the cable outlet for sealing. There is a water filling hole and an air vent hole at the upper end of the motor, and a drain hole at the lower part. Upper and lower thrust bearings are installed at the lower part of the motor. The thrust bearings have grooves for cooling and mate with stainless steel thrust discs to withstand the axial forces of the water pump.

DMC pump precautions for use

1) Install a residual current device (RCD): An RCD is also known as a life saver, and its function can be understood from this name. Since submersible pumps operate underwater, leakage can easily cause energy loss or even electric shock accidents. If an RCD is installed, as long as the leakage current of the submersible pump exceeds the trip current value of the RCD (generally not exceeding 30 mA), the RCD will cut off the power supply to the submersible pump, avoiding energy waste due to leakage and ensuring safety. 2) Do not start if the power supply voltage is abnormal: When low-voltage supply lines are long, low voltage at the end of the line is common. When the phase voltage is lower than 198 V and the line voltage is lower than 342 V, the speed of the submersible pump motor decreases. When it fails to reach 70% of the rated speed, the starting centrifugal switch will close, causing the starting winding to be energized for a long time, leading to overheating and even burnout of the windings and capacitors. Conversely, excessive voltage causes motor overheating and winding burnout. Therefore, during operation, the operator must monitor the power supply voltage. If it is more than 10% below the rated voltage or more than 10% above the rated voltage, the motor should be stopped to identify and rectify the fault. 3) Avoid frequent switching: Do not frequently switch the submersible pump on and off. When the electric pump stops, backflow occurs. Immediate restart will cause the motor to start under load, resulting in excessive starting current that can burn out the windings. Due to the high starting current, frequent starts will also burn out the submersible pump motor windings. 4) Do not allow the submersible electric pump to operate under overload for long periods: To avoid long-term overload, do not pump water with high sand content, and monitor whether the current value is within the rating specified on the nameplate. If the current is too high, stop the pump for inspection. Additionally, the running time of the electric pump without water should not be too long to prevent motor overheating and burnout. 5) Ensure correct motor rotation direction: Clarify the motor rotation direction. Many types of submersible pumps can discharge water in both forward and reverse rotation, but reverse rotation results in lower flow and higher current. Prolonged reverse rotation will damage the motor windings. 6) Cable installation and insulation resistance requirements for submersible electric pumps: When installing the submersible pump, keep the cable suspended and avoid excessively long power cords. Do not subject the cable to stress when lowering or lifting the submersible pump to prevent power cord breakage. Do not allow the submersible pump to sink into mud during operation, as this will cause poor motor heat dissipation and burn out the motor windings. During installation, the motor insulation resistance should not be less than 0.5 MΩ. 7) Inspect frequently and repair issues promptly: Regularly inspect the motor. If cracks are found in the lower cover, or if the rubber sealing ring is damaged or failed, replace or repair it promptly to prevent water from entering the submersible pump.

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