The construction of a mersible pump focuses on creating a watertight and durable unit capable of withstanding prolonged immersion and the hydraulic pressures of its operating depth. The core assembly consists of a multi-stage centrifugal pump section coupled directly to a specialized electric motor. Both are housed within a common shell, usually a long, narrow cylinder to fit into boreholes or standard sump liners. Critical to its function are the mechanical seals that isolate the motor chamber from the pumped fluid; these are often double seals with a barrier fluid for added protection in demanding applications.

Internal components are chosen for resilience. The motor windings are insulated with moisture-resistant materials, and the bearing system is lubricated by either a sealed oil reservoir or the pumped fluid itself. The impellers and diffusers are designed to generate the necessary pressure (head) to lift fluid from depth, with materials varying from engineered plastics for clean water to hardened metals for slurries. An intake screen protects the internal components from large solids, and a thermal overload switch within the motor provides protection against overheating.

Long-term performance requires attention to the operating environment. Running the pump outside its designed flow range can lead to overheating or accelerated wear. For challenging fluids like sewage, models with clog-resistant vortex impellers or cutting mechanisms are used. The specialized design and material choices for a mersible pump enable it to perform reliably in the demanding context of full submersion, offering a practical solution for deep and difficult pumping tasks.