A submersible pump is a hermetically sealed motor-pump unit designed to operate while fully submerged in the fluid it is intended to move. This fundamental design characteristic distinguishes it from other pump types that are installed dry and rely on suction to draw fluid. The core advantage of a submersible pump lies in its efficiency and reliability for deep or continuous pumping applications. Because the pump is placed directly within the fluid source, it pushes liquid to the surface rather than pulling it, which eliminates problems like suction lift limitations and priming issues commonly associated with above-ground pumps. This makes a submersible pump particularly effective for extracting water from wells, managing floodwater, or handling industrial fluids in sumps or tanks.

The construction of a durable submersible pump involves several critical layers of protection. At its heart is an electric motor, specifically engineered to be waterproof. This motor is sealed within a watertight casing, often filled with dielectric oil that provides lubrication, cooling, and prevents internal condensation. Directly coupled to the motor shaft is the pump section, which can utilize various impeller designs such as centrifugal, mixed-flow, or axial-flow, depending on the required flow rate and pressure. The entire assembly of a submersible pump is typically long and cylindrical to fit into narrow boreholes or sump pits. Materials are chosen for corrosion resistance; stainless steel is common for residential water systems, while industrial submersible pumps may use specialized alloys or coated cast iron to handle abrasive or chemically aggressive fluids.

Installation and operation of a submersible pump require specific considerations. For well applications, the pump is lowered into the drilled borehole and suspended by its discharge pipe and a safety cable. The electrical cable, which supplies power to the submerged motor, is specially rated for continuous immersion. Once activated, the motor drives the impellers, which draw fluid in through a screened intake, impart energy to it, and discharge it upwards through the column pipe. A control system, usually located above ground, houses starting components and protection devices like overload relays. The submersible pump runs quietly because it is submerged, and its cooling is provided by the surrounding fluid, which is more effective than air cooling. This design allows a submersible pump to operate efficiently at significant depths, providing a steady and reliable flow for water supply, dewatering, and irrigation systems where other pump types would be impractical or inefficient.