Submerged pump, also called submersible pump, is a very versatile water and slurry treatment tool. The difference between submerged pump and ordinary water pump machine is that submerged pump work underwater, while most water pump machine work on the ground. Before the submerged pump is turned on, the suction pipe and the pump body must be fully filled with liquid. After the submerged pump is turned on, the impeller rotates at a high speed, and the liquid in the submerged pump rotates with the blades. Under the action of centrifugal force, the liquid flies away from the impeller and shoots out, the speed of the ejected liquid gradually slows down in the diffusion chamber of the submerged pump casing, and the pressure gradually increases. Then the liquid flows out from the submerged pump outlet and the discharge pipe. At this time, a vacuum low-pressure area with neither air nor liquid is formed at the center of the blade due to the liquid being thrown around. Under the action of the atmospheric pressure on the pool surface, the liquid in the pool flows into the submersible pump through the suction pipe. In this way, the liquid is continuously sucked up from the liquid pool and continuously flows out from the discharge pipe. The basic parameters of submerged pump include flow, head, pump speed, supporting power, rated current, efficiency, pipe diameter, etc. Submerged pumps are widely used in daily life, such as construction drainage, agricultural irrigation and drainage, industrial water circulation, water supply for urban and rural residents, and even rescue and disaster relief.

The Working Principle and Characteristics of submerged pump machine
The Working Principle and Characteristics of submerged pump
The Working Principle and Characteristics of submerged pump
The Working Principle and Characteristics of submersible pump

1. Characteristics and Type of Submerged Pump

The submersible motor of the submerged dredging pump has special requirements compared with the general motor. Usually, there are several types of submersible motor such as dry, semi-dry, wet, oil-filled and air-cushioned motors.

A. The dry motor is not different from the general motor except that the winding insulation is strengthened to prevent moisture. Since the dry submersible motor does not allow the transported liquid to enter the inner cavity of the motor, it is necessary to take good sealing measures at the shaft extension end of the motor. Usually a mechanical sealing device is used. But due to the complex structure of this sealing device and the high processing requirements, if the water contains mud and sand, the sealing member is easily worn out, resulting in seal failure. Therefore, it is better to use a mechanical seal when pumping clean water without mud and sand.

B. For semi-dry motor, only the stator of the motor is sealed, and the rotor is rotated in the water.

The inner cavity of the stator of the wet motor is filled with clean water or distilled water, and the rotor rotates in the clean water. The stator is made of polyethylene, nylon and other waterproof insulated wires. In order to solve the cooling problem of motor windings and water-lubricated bearings, the inner cavity of the motor is filled with clean water. Therefore, the shaft seal of this submerged pump only plays the role of preventing mud and sand from entering the motor, and the advantage is that the structure is relatively simple, which is convenient for manufacture and maintenance. However, this kind of submerged pump has high requirements on the insulated wires and water-lubricated bearing materials used in the motor stator, and it is necessary to consider the problem of rust prevention of components.

C. The feature of the oil-immersed submersible pump is that the motor is fully filled with insulating paint (such as transformer oil) to prevent water and moisture from entering the motor winding, and play a role of insulating, cooling, lubricating and preventing water and moisture from entering the motor cavity. At the same time, a mechanical seal at the shaft extension end of the motor is still necessary to prevent the entry of water and sand, and the leakage of oil. The motor stator coil is wound with oil-resistant and water-resistant enameled wire with reinforced insulation. The motor rotor of this kind of submerged pump rotates in the oil with high viscosity, resulting in large power loss, and a decrease in efficiency, generally about 3%-5%.

D. The characteristics of the air-cushion sealed submersible pump are as the same as those of the dry motor submersible pump, but there is an air-sealing chamber at the lower end of the motor, which is communicated with the outside world by several holes. After the submerged dredging pump dives into the pool, the air in the air-sealing chamber forms an air cushion under the action of the external liquid pressure to prevent the liquid from entering the inner cavity of the motor. This kind of submersible pump is only suitable for situations with small and stable diving depth, and the sealing method has the danger of water entering the inner cavity of the motor due to the dissolution of air, so it is rarely used.

Many types of underwater pumps are equipped with automatic coupling devices. At the submerged pump outlet end,  there are rollers that roll up and down in the guide rails. The maintenance work of the submerged pump can be carried out outside the pool. The lower end of the vertical guide rail is fixed on the elbow support, and the upper end is welded and fixed with the pre-embedded steel plate in the top beam or wall of the sewage pool (the side of the outlet elbow). The bearing is shared with the submersible motor. The shaft seal adopts mechanical seal, the transmission is coaxial with the submersible motor, and is directly driven by the motor.

The Working Principle and Characteristics of underwater suction pump
The Working Principle and Characteristics of underwater pump
The Working Principle and Characteristics of underwater dredging pump

2. The Selection of Submerged Pump

Submerged pumps play an important role in production and life. When purchasing a submerged dredging pump, pay attention to its model, flow and head. If the selected specifications are not appropriate, the water output is insufficient, and the efficiency of the submersible pump unit cannot be exerted. In addition, please check the direction of rotation of the motor. Some types of submerged pumps can extract water in both forward and reverse rotations, but when reversed, the water output is small and the current is large, the reverse rotation will damage the motor windings. In order to prevent electric shock accidents caused by electric leakage when the submersible pump is working underwater, a leakage protection switch should be installed.

3. Use of Submerged Pump

A. When installing a small submerged dredging pump, the cable should be overhead, and the power cable should not be too long. The cable should not bear the force when the underwater pump is diving, so as not to cause the power cord to break. Do not sink the submerged dredging pump into the mud, otherwise it will cause poor heat dissipation and burn out the motor windings.

B. Try to avoid starting at low voltage. The power supply voltage and the rated voltage should not differ by 10%. Excessive voltage will cause the motor to overheat and burn out the windings. Too low voltage will cause the decrease of the motor rotation speed, If it does not reach 70% of the rated speed, the starting centrifugal switch will be closed, causing the starting winding to heat up or even burn out the winding and capacitor due to long-term energization. Do not switch the motor on and off frequently, because backflow will occur when the submerged pump stops. If it is turned on immediately, the motor will start with a load, resulting in excessive starting current and burning out the windings.

C. The submerged pump can not be overloaded for a long time and can not pump water with high and content. The time that the submerged dredging pump runs away from the water should not be too long, so as not to cause the motor to overheat and burn out. When the submersible pump unit is working, the operator must observe whether the working voltage and current are within the values specified on the nameplate at any time. If it does not meet the requirements, the motor should be stopped, find out the reason and eliminate the fault.

D. Check the motor frequently. If there are cracks, rubber sealing ring damage or failure in the lower cover, please replace or repair it in time to prevent water from infiltrating the submerged dredging pump.

The Working Principle and Characteristics of submerged dredge pump
The Working Principle and Characteristics of submersible dredge pump
The Working Principle and Characteristics of submerged dredging pump

Tai’an Ocean Pump Co., Ltd. (referred to as OCEAN PUMP) is a manufacturer and exporter of sand pumps, wear-resistant gravel pumps, slurry pumps, mud pumps, sediment pumps, submersible sand pump, sewage pumps, dredging pumps, sand dredgers and other sand pump machine. OCEAN PUMP integrates independent research and development, equipment manufacturing, pre-sales and after-sales service, the business covers sand suction and dredging projects. The products cover 20 series and more than 500 specifications. The products are exported to 36 countries and regions. OCEAN PUMP has won the praise and trust of users with its more than 20 years industry experience, professional technology and excellent service.