What a submersible pump does and where it sits

A submersible well pump is a sealed electric motor attached directly to a pump that sits underwater, deep inside your well. Unlike jet pumps that sit above ground and pull water up through a pipe, a submersible pump pushes water up from below. The motor and pump are one unit, lowered on a single pipe into the well casing until they rest near the bottom, where water is most plentiful.

The pump stays submerged at all times. Water surrounds the motor housing, which is sealed and pressurized to keep electricity and water apart. A single electrical cable runs from the pump up to the surface, where it connects to a pressure tank and control box in your house or pump shed.

Key Takeaways

  • A submersible pump sits underwater in your well and pushes water upward through a single pipe, unlike surface pumps that pull water from above.
  • The motor and pump are sealed together as one unit, with water pressure helping to cool the motor as it runs.
  • An impeller inside the pump spins rapidly to force water into progressively smaller chambers, building pressure that sends water to your house.
  • The pump turns on and off automatically when pressure in your tank drops below or rises above a set range, usually 40 to 60 pounds per square inch.
  • Submersible pumps last longer than surface pumps because they are protected from freezing, sunlight, and temperature swings underground.

The motor and how it stays safe underwater

The electric motor inside a submersible pump is completely sealed in a steel or cast-iron housing. The housing is filled with a special oil that does not conduct electricity, so even though water surrounds the outside, the electrical windings inside stay dry and insulated. This oil also acts as a coolant, absorbing heat from the motor as it runs.

Water itself helps cool the pump. As the motor works, heat moves through the sealed housing into the surrounding groundwater, which is usually cold year-round. This natural cooling means submersible pumps can run longer without overheating than surface pumps, which rely only on air circulation. The deeper the well, the colder the water, and the better the cooling.

How the impeller forces water upward

Inside the pump body, a spinning part called an impeller does the actual work of moving water. The impeller looks like a small turbine or fan with curved blades. As the motor spins it at high speed—typically 1,200 to 3,600 revolutions per minute—the blades push water outward and upward into a chamber called a diffuser.

The diffuser is shaped like a spiral or a series of narrowing passages. As water enters at high speed, the passages slow it down and squeeze it into a smaller space. This squeezing converts the water's speed into pressure—the same principle that makes a garden hose spray harder when you pinch the nozzle. That pressure pushes water into the next stage of the pump, and the process repeats.

Most submersible pumps have multiple stages—often four to ten impellers and diffusers stacked inside the same housing. Each stage adds more pressure. A single-stage pump might produce 30 pounds of pressure; a ten-stage pump can produce 300 pounds or more. The deeper your well, the more stages you need to push water all the way to the surface and into your house.

How pressure builds and water reaches your house

As each stage of the pump adds pressure, water is forced up through a single pipe—called the discharge pipe or riser pipe—that runs from the pump at the bottom of the well all the way to the surface. The pipe may be 50, 100, or even 300 feet long, depending on your well depth.

At the surface, the water enters a pressure tank, a sealed metal container that holds both water and compressed air. As water fills the tank, it compresses the air inside. This air pressure pushes back on the water, and that pressure is what forces water out of your faucets and showers when you turn them on. The pressure tank acts as a buffer, so the pump does not have to run every time you use a small amount of water.

A pressure switch monitors the air pressure inside the tank. When pressure drops to a set low point—usually around 40 pounds per square inch—the switch turns the pump on. When pressure rises to a set high point—usually around 60 pounds per square inch—the switch turns the pump off. This on-and-off cycling keeps water available and ready without running the pump constantly.

Why submersible pumps last longer than surface pumps

Because a submersible pump lives underground, it avoids many of the problems that wear out surface pumps. It does not freeze in winter because groundwater stays above freezing even when air temperature drops far below zero. It does not bake in summer sun or suffer temperature swings that crack seals and hoses. It is not exposed to rain, dust, or rust-causing moisture in the air.

The sealed design also means fewer moving parts are exposed to wear. A surface pump has a long intake line that can clog, crack, or lose its prime. A submersible pump has one pipe doing one job, with no priming needed. The water surrounding the pump keeps it cool, so the motor does not overheat even during long, hot days when demand is high.

Most submersible pumps last 15 to 25 years if the well is properly maintained and the pump is sized correctly for your household's water use. A pump that is too small will run constantly and wear out faster. A pump that is too large will cycle on and off too often, which also shortens its life.

What can go wrong and how to spot it

The most common failure in a submersible pump is a leak in the sealed motor housing. If water gets inside, it corrodes the windings and the motor stops working. You may notice the pump running but no water coming out, or water coming out very slowly. This usually means the pump has failed and needs to be pulled from the well and replaced.

Sand or sediment in the well can damage the impeller blades and reduce water pressure over time. If your water pressure drops gradually and your well is shallow, sediment may be the cause. A well contractor can test the water and, if needed, have the well cleaned or the pump replaced with a model that handles sediment better.

Electrical problems are also common. If the pressure switch fails, the pump may not turn on when pressure drops, leaving you without water. If the electrical cable is damaged or the breaker trips repeatedly, the pump will not run. These are usually signs to call a well service company rather than try to fix them yourself.

Frequently Asked Questions

Why does my submersible pump need a pressure tank?

The pressure tank stores water and compressed air so that water pressure stays steady in your pipes. Without it, the pump would have to turn on and off every time you opened a faucet, which would wear it out much faster and create annoying pressure surges. The tank lets you draw small amounts of water without the pump running.

Can I replace a submersible pump myself?

Pulling a pump from a deep well and lowering a new one requires special equipment and knowledge of electrical connections. Most homeowners should hire a licensed well contractor. The pump is heavy, the electrical work is dangerous, and mistakes can damage the well casing or leave you without water for days.

How deep can a submersible pump push water?

A single-stage pump can typically push water about 25 to 30 feet. Each additional stage adds roughly 25 to 30 feet of lift. A ten-stage pump can push water 250 to 300 feet or more. Your pump is sized based on your well depth, so if your well is 200 feet deep, you need a pump with enough stages to reach that depth plus overcome the pressure needed for your house.

What does it mean if my pump is running but water pressure is low?

Low pressure while the pump runs can mean sediment is clogging the impeller, a valve is partially closed, or the pump is straightforward too small for your household's water use. It can also mean the pressure tank is waterlogged—filled with water instead of air—which prevents it from building pressure. A well contractor can diagnose which problem you have.

How often should a submersible pump be serviced?

Most submersible pumps do not need routine service if they are working correctly. However, you should have your well water tested yearly for bacteria and sediment, and your pressure tank inspected every few years to make sure the air charge is correct. If the pump is more than 15 years old, ask a contractor to evaluate whether replacement is coming soon.