Submersible Pump
General / GeneralDefinition
A submersible pump has a hermetically sealed motor closely coupled to the pump body, with the entire assembly designed to operate while fully submerged in the pumped liquid. The motor is cooled by the surrounding fluid, and the close-coupled design eliminates the need for a long drive shaft between the surface and the pump. Submersible pumps range from small residential sump pumps to large industrial units handling raw sewage, mine dewatering, and deep-well water supply at depths exceeding 1,000 feet.
Working Principle
The electric motor sits below (or beside) the pump impeller in a sealed housing filled with dielectric oil or air. Motor cooling relies on heat conduction through the housing wall to the surrounding liquid. The pump intake draws fluid through a strainer or suction bell, and one or more impeller stages increase pressure. The discharge pipe (column pipe) carries the fluid to the surface. Because the entire unit is submerged, there is no need for priming — the pump is always below the liquid level. A mechanical seal (or two seals in tandem) prevents fluid from entering the motor along the shaft. Most submersible pumps are centrifugal, though progressive cavity and mixed-flow designs exist for specific applications.
Key Components
| Motor | Sealed, cooled by surrounding fluid; 2-pole or 4-pole induction |
| Mechanical seal | Double seals prevent fluid entry into motor |
| Impeller(s) | Single or multi-stage centrifugal; enclosed or semi-open |
| Pump casing / bowl | Houses impeller(s); volute or diffuser design |
| Suction strainer | Prevents debris from entering the impeller |
| Discharge column | Pipe carrying fluid to surface; also supports the unit |
| Power cable | Waterproof cable supplying power to the submerged motor |
| Check valve | Prevents backflow when pump stops |
Types & Variants
| Type | Impeller | Application | Capacity | Head |
|---|---|---|---|---|
| Borehole / Deep well | Multi-stage enclosed | Water supply from deep aquifers | 5-500 GPM | 100-1500 ft |
| Wastewater / Sewage | Single or 2-stage, open/vortex | Raw sewage, stormwater | 50-20,000 GPM | 10-200 ft |
| Sump / Drainage | Single stage, open | Basement drainage, construction dewatering | 10-500 GPM | 10-50 ft |
| Mine dewatering | Multi-stage, high-pressure | Underground mine water removal | 100-5,000 GPM | 200-2,000 ft |
| Industrial process | Various, chemical-resistant | Chemical sumps, tank emptying | Varies | Varies |
Materials
Cast iron motor and pump housing for general water and sewage service. Stainless steel (304 or 316) for corrosive wastewater and chemical applications. Bronze for seawater and marine service. Duplex stainless for high-chloride, high-sulfide sewage. Motor windings: Class H insulation (200C rating) for high-temperature service. Mechanical seals: silicon carbide vs. carbon for general service; SiC vs. SiC for abrasive sewage. Power cables: heavy-duty submersible cable with oil-resistant jacket (THW, SOW, or W series).
Applicable Standards
API 610 (Centrifugal Pumps) applies to some industrial submersibles. EN 12050/12051 covers submersible pumps for wastewater. UL 778 and CSA C22.2 for electrical safety in North America. IEEE 841 for severe-duty motors (some submersible motors reference this). NEMA MG 1 for motor design standards. EPA guidelines for sewage pump station design.
Applications
Municipal wastewater lift stations: submersible sewage pumps are the standard, replacing old dry-pit installations with wet-well submersibles that save construction cost and eliminate the dry well. Deep well water supply: borehole submersible pumps provide drinking water from aquifers at depths of 100-1,500 feet. Mine dewatering: high-head multi-stage subm