Structure and Working Principle of Submersible Pumps

  A submersible pump, also called a submersible electric pump, is a widely used water treatment tool that finds applications in both agricultural production and industrial processing. It can be roughly categorized into submersible sewage pumps, submersible sand pumps, and submersible clean water pumps based on application scenarios and purposes.

A submersible pump generally consists of a pump body, a discharge pipe, a pump base, a submersible motor, and a starting protection device. Simply put, it is a liquid-conveying machine that integrates a pump and a motor, featuring a simple structure and easy operation.

Submersible pumps have a history of over 60 years of development. In 1904, Byron Jackson Company of the United States successfully designed and manufactured the first horizontally connected submersible electric pump and submersible motor, which are regarded as the "ancestors" of modern submersible electric pumps. With the development of materials science, sealing technology, control and protection technology, as well as the improvement of hot and cold processing techniques, submersible electric pumps have achieved rapid development. In 1928, the company invented the vertically connected submersible electric pump, which was the initial form of modern deep-well submersible electric pumps. In China, Shanghai People's Electric Machinery Factory began producing 7KW face submersible electric pumps in 1958, marking the start of domestic submersible electric pump production. After more than 30 years of development, remarkable achievements have been made in this field.

According to the relative position of the pump and the motor, submersible pumps can be further divided into top-pump type and bottom-pump type.

For the top-pump type submersible pump, the pump is mounted on top and the motor at the bottom. This structure greatly reduces the radial dimension of the pump, making it suitable for well submersible electric pumps and small-sized face submersible electric pumps.

For the bottom-pump type submersible pump, the motor is installed on top and the pump at the bottom. It can be further classified into internal type and external type.

For the internal bottom-pump type submersible electric pump, the conveyed liquid first passes through the annular flow channel surrounding the motor to cool the motor before flowing out from the pump outlet. Even when the suction sump is nearly drained, there is no need to worry about motor overheating, so its application range is expanding day by day.

For the external bottom-pump type submersible electric pump, the liquid is directly discharged from the volute chamber behind the impeller or the outlet of the guide vane body, and the motor is also cooled by the pumped liquid. Thanks to its ability to operate in shallow liquid, this type is often used for face submersible electric pumps, and it is especially the main structural type for large-caliber submersible electric pumps.

The mechanical seal of the bottom-pump type submersible electric pump is located in the high-pressure area of the outlet water flow. The higher the lift, the higher the water pressure at this point, so the performance of the mechanical seal is subject to the limitation of the lift.

Submersible Pumps: Applications Based on Impeller Structure Characteristics

The application scenarios of submersible pumps vary according to the structural characteristics of their impellers.

Open or Semi-open Impellers

Manufactured from wear-resistant materials, these impellers are equipped with adjustable guide vanes and filters. They are widely used for water supply, drainage, or water jetting in construction sites, tunnels, ports, factories, ships, and other settings, and are capable of pumping liquid media containing abrasives such as clay, sand, gravel, and drilling cuttings.Featuring a mobile structure, these pumps can be started immediately after being placed in water. They are suitable for special requirements such as large flow rates, high heads, limited installation spaces, or explosive environments.

Non-clogging Closed-channel Impellers

These impellers offer excellent reliability and high efficiency. They are mainly used in urban pumping stations and sewage treatment plants for conveying sewage and sludge, in industrial processes for transferring cooling water, wastewater, and corrosive media, and for continuous drainage at construction sites and large-scale factories. They are particularly suitable for pumping media containing long-fiber substances and large solid particles.These pumps can be installed in small, simple pumping stations and concealed underground. They can be quickly and easily mounted on guide rails or cables and lowered into pump sumps.

Open Impellers with S-type Cutters

These impellers integrate the functions of pumping, cutting, and mixing, boasting high reliability and efficiency. They are primarily used in agriculture for pumping liquid manure, as they can crush dry solids, straw, and other long-fiber materials. The spiral-shaped impeller inlet allows thick manure to be drawn into the pump smoothly. There are four specifications available in total.With a compact structure, these pumps can be installed on guide rails inside manure pits or storage tanks, and can also be used in conjunction with submersible mixers.

Multi-vane Closed Impellers

Cast from cast iron or stainless steel, these impellers feature single-sided or double-sided (double-suction) water inlets. They are especially suitable for agricultural sprinkler irrigation and various industrial applications, such as supplying clean water, process water, jetting water, and cooling water.They can meet the requirements of high head and large flow rate, with a maximum flow rate of 2,000 m³/h and a maximum head of 110 m. Ideal for pumping clean water or slightly contaminated water, they are available in a wide range of specifications and structural types, offering strong performance, high reliability, and easy installation and maintenance.

Submersible Pump Impellers: Types, Characteristics and Applications

Adjustable Blade Axial-flow Impellers

These impellers are characterized by high efficiency and energy saving. They are mainly used for agricultural irrigation, urban water supply and drainage, industrial cooling water circulation, and can also be applied to the control of inland waterway systems. They are designed to meet the special requirements of low head and large flow rate, and are suitable for pumping clean water or slightly contaminated water.

Their structure is compact and simple, requiring no special installation—they only need to be lowered and seated on the shoulder of the casing base.

Open Impellers with Integrated Shredding Device

These open impellers are fitted with a shredding device at the inlet, which is made of chromium alloy and stainless steel. They are especially suitable for pressurized sewage systems, as the shredded media can be transported through pipes with a diameter of only 40 mm.

Closed-channel Impellers

Matched with guide vanes, these impellers deliver excellent reliability. They are widely used for water supply and drainage in urban areas, agriculture, ships and industrial facilities, and can meet the demand for low head and large flow rate (with a maximum flow rate of 2,000 m³/h). Ideal for pumping clean water or slightly contaminated water, they are available in six specifications.

They feature a pipeline-free connection design for easy installation and maintenance.

Abrasion-resistant Open or Closed-channel Impellers

Manufactured from wear-resistant materials, these impellers are mainly used in mines, construction sites, tunnels and dams to pump liquids containing abrasive particles such as drilling cuttings, sand and gravel. The suction end is equipped with an adjustable rubber lining, which helps maintain operation at the high-efficiency point.

Multi-vane Open or Closed Impellers

Equipped with multiple blades, these impellers are primarily used for surface drainage in basements and other areas, as well as for irrigation purposes. They are designed to meet the requirements of small flow rate and moderate head, and are suitable for pumping clean water or slightly contaminated water. Three specifications are available in total.

With a compact structure, they are easy to install—simply place the pump at the bottom of the sump.

The model designation of submersible pumps is straightforward, usually consisting of just three sets of numbers. For example, the model 25-8-22 indicates the following parameters:

Outlet diameter: 25 mm

Flow rate: 8 m³/h

Head: 22 m

Power: 1.1 kW

Rotational speed: 2900 r/min

Voltage: 380 V

In general, the rated voltage of submersible pumps is 380 V, except for special-purpose models. Other common models include 32-10-15, 40-15-30, 50-20-7, and up to 300-800-20.

Key Considerations for Submersible Pump Selection

Special attention must be paid to the model, flow rate and head during selection. An improperly selected pump will fail to meet operational requirements and cannot achieve optimal unit efficiency.

It is also critical to confirm the correct rotation direction of the pump. While many submersible pump models can discharge water in both clockwise and counterclockwise rotations, reverse rotation will result in reduced water output, increased current draw, and may even damage the motor windings in severe cases.

Installation and Operational Precautions

Cable HandlingWhen installing the pump, the power cable should be suspended overhead, and the cable length should not be excessively long. Never allow the cable to bear tension when lowering the unit into water to prevent cable breakage.

Installation PositionDo not submerge the pump in sludge; otherwise, poor heat dissipation will cause the motor windings to overheat and burn out.

Voltage Requirements

Avoid starting the pump under undervoltage conditions. Low voltage leads to reduced rotational speed—if the speed drops below 70% of the rated value, the centrifugal switch will remain closed, causing the starting winding to overheat and even burn out, along with the capacitor.

Do not start the pump under overvoltage conditions, as this will cause the motor to overheat and damage the windings.

Start-stop OperationDo not switch the motor on and off frequently. When the pump stops, backflow occurs; restarting immediately will subject the motor to load starting, resulting in excessive starting current that can burn the windings.

Load LimitationsDo not operate the pump under overload conditions for extended periods. Avoid pumping water with high sand content. The pump should not run dry for too long, as this can lead to motor overheating and burnout.

Operational MonitoringDuring operation, the operator must continuously monitor whether the working voltage and current are within the ranges specified on the nameplate. If not, stop the motor immediately, identify the cause, and troubleshoot the issue.

Routine Maintenance

Inspect the motor regularly. If cracks are found on the lower cover or the rubber sealing ring is damaged or ineffective, replace or repair the parts promptly to prevent water from seeping into the unit.

Monitor the water level in the well frequently during operation. The motor must never be exposed above the water surface or submerged in sludge, both of which will impede heat dissipation and burn the windings. Adjust the pump’s depth in real time according to water level changes. If water output decreases or stops suddenly, investigate the cause immediately or shut down the pump for inspection.

Prevent the cable from rubbing against the well wall to avoid abrasion—once the cable is damaged, well water will seep into the motor through the cable core.

After one year of use, inspect the pump for corrosion, remove rust, and apply anti-corrosive paint.

For long-term storage, thoroughly inspect the submersible pump and store it in a dry, well-ventilated room.