A submersible pump is a specialized machine where the motor and the pump are sealed together in a watertight assembly, allowing the entire unit to be fully submerged in the fluid it moves. This design is advantageous because the surrounding liquid helps keep the motor cool, preventing overheating. Unlike pumps that rely on suction to pull liquid upward, a submersible pump operates by converting rotational energy into pressure energy, efficiently pushing the fluid to the surface. This fundamental difference makes the submersible design significantly more efficient, especially when moving liquids from deep sources.
Supplying Water from Wells and Cisterns
Submersible pumps are the preferred choice for drawing potable water from deep wells and cisterns. Submerged placement near the bottom of the water source means the pump does not waste energy overcoming the atmospheric pressure limitations faced by above-ground jet pumps. Submersible units can effectively lift water from depths exceeding 400 feet, whereas jet pumps are limited to depths shallower than 120 feet. This ability ensures a consistent flow rate and pressure at the surface, regardless of the well’s depth.
Proper selection of a well pump depends on the required flow rate (gallons per minute, GPM) and the total pressure needed, referred to as the Total Dynamic Head (TDH). The TDH calculation accounts for the vertical distance the water must be lifted, the pressure required at the point of use, and the friction loss within the piping system. Matching the pump’s horsepower to this specific “design point” is more important than selecting a high-horsepower motor, as an improperly sized pump will operate inefficiently. A common residential pump may be a 1-horsepower unit designed to deliver 25 GPM from a depth of 300 feet.
The pump uses a series of stacked impellers and diffusers to build pressure incrementally, making it a multi-stage centrifugal pump. This configuration allows the pump to generate the necessary lift to overcome the static head pressure of a deep well. Since the pump is submerged, maintenance requires pulling the entire assembly out of the well casing, a more complex task than servicing an above-ground pump. Despite the higher cost and complexity of installation, the long-term energy savings and reliability make it the standard for deep water retrieval.
Emergency Drainage and Sump Applications
Submersible pumps manage unwanted water in residential and commercial settings, primarily through fixed sump pump installations and portable utility pumps. A standard sump pump is permanently located in a sump pit at the lowest point of a basement or crawlspace. Its purpose is to collect groundwater that seeps in around the foundation, preventing interior flooding and managing the local water table.
These fixed units operate automatically using a float switch or pressure sensor that triggers the pump when the water level reaches a predetermined height. The pump then rapidly discharges the collected water through a pipe and away from the foundation. Submersible sump pumps are preferred over pedestal models because their submerged motor is cooled by the surrounding water, making them quieter and more powerful for higher-volume dewatering tasks. They handle relatively clean water or “gray water,” which may contain small suspended particles but not large solids.
For temporary water removal, portable submersible utility pumps offer a flexible solution. These lightweight pumps are not permanently installed and can be easily moved to drain a variety of sources. Common uses include emptying a hot tub or swimming pool, removing standing water from a flooded yard, or clearing a basement after a temporary plumbing failure. Utility pumps are designed for rapid dewatering and can be connected to a standard garden hose for discharge.
Moving Waste and Effluent
Submersible pumps are engineered to handle wastewater containing solids, a task requiring specialized construction to prevent clogs. These pumps are classified based on the type and size of solid material they are built to manage, from treated wastewater to raw sewage. Effluent pumps are used in septic systems to move liquid that has passed through a septic tank, where the majority of solids have settled out. The effluent is then pumped to a drain field or a spray irrigation system.
For lifting raw sewage, two other types of submersible pumps are employed: sewage ejector pumps and grinder pumps. Sewage ejector pumps utilize a specialized non-clog or vortex impeller with large clearances, allowing them to pass soft solids up to two inches in diameter without obstruction. These are commonly installed in basement bathrooms where the fixtures are below the main sewer line.
Grinder pumps represent the most robust design, incorporating a powerful cutting mechanism that shreds solid waste, including fibrous materials, into a fine slurry before it enters the pump housing. This maceration process allows the pump to discharge the waste through smaller diameter pipes, making them suitable for low-pressure sewer systems or when pumping over long distances or high vertical lifts. They are reserved for applications where the force and pressure required to move the finely ground waste is substantial.