A submersible well pump spends its whole life underwater at the bottom of a well, which is both why it works so well and why nobody thinks about it until it stops.
Specifying one is mostly about three numbers and one decision. Get those right and the pump is close to invisible for a decade or more.
How Does a Submersible Well Pump Work?
A submersible well pump sits below the water and pushes water up the drop pipe instead of pulling it from the surface. Stacked impellers, each called a stage, add pressure in series, so a deeper well is answered with more stages rather than a bigger motor.
Key Takeaways
- Submersibles push rather than pull, so depth is not the barrier it is for surface pumps.
- They never need priming, because they are always full of water.
- Size on pumping water level, household flow and tank pressure.
- Well yield caps everything. No pump beats the well.
- Two wire and three wire motors are not interchangeable.
The Three Numbers That Size a Pump
| What to measure | Why it matters | Where people go wrong |
|---|---|---|
| Pumping water level | Sets the lift, and therefore the stages | Using the static level instead |
| Flow needed (GPM) | Sets the pump curve | Adding every fixture rather than peak use |
| Pressure at the tank | Adds to total head | Forgetting it entirely |
| Well yield | Caps what is possible | Specifying above what the well gives |
The first row causes most oversizing. Static level is where the water sits at rest; pumping level is where it settles while the pump runs, and it is always lower. Size on the static figure and the pump is working harder than the specification says for its whole life.
The last row is the one nobody can engineer around. If the well yields 8 gallons per minute, a 15 gallon pump will draw it down and start sucking air, which is the fastest way to destroy a submersible.
Two Wire or Three Wire?
Two wire motors carry their starting components inside the motor and need no control box. Three wire motors put those components in a box above ground, which means a failed capacitor is an afternoon rather than a well rig.
That is the practical argument for three wire on anything but the smallest installation, and the components themselves are covered in our guide to the well pump control box. The two types are not interchangeable, so the wire count is read off the motor nameplate before anything is ordered.
Submersible or Jet Pump?
The alternative for shallow water is a surface jet pump, and the dividing line is roughly 25 feet. Below that depth atmospheric pressure can no longer push water up a suction line, which is a physical ceiling rather than a question of power.
Jet pumps win on access, since everything is above ground and serviceable with hand tools. Submersibles win on depth, efficiency and noise. The full comparison is in our look at shallow well jet pumps, and the broader family differences in submersible against centrifugal designs.
Installation Details That Decide Its Life
- Set the pump above the well bottom, commonly 10 to 20 feet up, so it is not drawing sediment.
- Size the drop cable for the run. Undersized wire drops voltage and burns motors.
- Fit a torque arrestor so the starting twist does not chafe the cable against the casing.
- Use a safety rope. Pumps do get dropped, and retrieval is expensive.
- Protect against dry running, since the pumped water is also the motor coolant.
Voltage drop is the quiet killer among these. A motor fed through cable that is one size too small for the depth runs hot for years and fails early, and nothing in the well gives you any warning. The mechanical background is set out in this overview of submersible pumps.
When It Starts to Fail
Falling pressure, air spitting at the taps or a pump that runs without delivering all point somewhere specific, and the order you check them in saves money. The full diagnostic sequence is in our guide to telling whether a well pump is bad, and the service routine that prevents most of it in maintaining a Franklin submersible.
Frequently Asked Questions
How does a submersible well pump work?
A submersible well pump works by sitting underwater at the bottom of the well and pushing water up the drop pipe rather than pulling it from the surface. Stacked impellers, called stages, each add pressure, so a deeper well simply needs more stages. Pushing instead of pulling is why depth is not the limit it is for a surface pump.
Do you have to prime a submersible well pump?
No, you do not have to prime a submersible well pump, because it is already underwater and full of the liquid it moves. Priming only applies to surface pumps that have to draw water up a suction line. If a submersible is running without delivering, the water level has dropped below it or the pump itself has failed.
What size submersible well pump do I need?
Size a submersible well pump on three numbers: the depth to the pumping water level, the flow your household needs, and the pressure you want at the tank. Most homes are served by a half to one horsepower unit delivering around 10 gallons per minute. Well yield sets the ceiling, since no pump delivers more than the well produces.
How many amps does a submersible well pump draw?
A submersible well pump draws roughly 5 to 10 amps at 230 volts for the half to one horsepower sizes used in most homes, though the motor nameplate is the figure that counts. Amp draw is also the best field diagnostic you have: readings well above or below the nameplate point at a binding pump or a worn one.
Submersible Well Pumps at Ken’s Distributing
Ken’s Distributing stocks 4 inch submersible well pumps alongside the motors, control boxes and drop cable that go with them, within the wider Franklin Electric range.
Send us the well depth, the pumping level if you have it, and the flow you need, and we will confirm the horsepower and stage count rather than guessing upward.
Submersibles are one family among several, and how they fit the rest is explained in Franklin’s pump families.