How Does a Well Pump Work? Submersible vs. Jet Explained
There are two kinds of well pumps, and they work on opposite principles. A submersible pump lives down in the well, submerged below the water level, and pushes water up. A jet pump sits above ground in the house or pump house and pulls water up by suction. Everything else — the noise, the maintenance, which one your well uses — flows from that one difference.
If you just want the machinery explained and nothing else, you're in the right place. For the full system around the pump (casing, pressure tank, pressure switch), read the companion guide on how your well water system works.
The core idea: no pump actually sucks
Here's the physics that governs everything. No pump "sucks" water the way a straw seems to. What a surface pump does is create a partial vacuum in its suction pipe — and the atmospheric pressure pushing down on the water surface in the well shoves the water up into the pipe. The pump makes the low-pressure zone; the atmosphere does the lifting.
Atmosphere only pushes so hard. At sea level it can support a column of water about 34 feet tall, and that's the absolute theoretical limit. In practice, a well-designed pump reliably manages about 25 feet of suction lift, and less at higher elevations where the air is thinner. That ceiling is the entire reason the two pump families exist: anything with a water level deeper than ~25 feet needs the pumping to happen down in the well, not at the surface.
A submersible dodges the suction problem completely. It's sitting in the water, so there is no lift at all on the intake side — it just pressurizes the water around it and pushes it up the drop pipe. Pushes have no atmospheric ceiling. That's why submersibles work at essentially any residential depth.
The submersible: a sealed motor with a stack of impellers
Picture a long metal cylinder, a few inches across and a few feet long, hanging in the well on the end of the drop pipe, below the water level. The unit has two ends: the motor on the bottom and the pump end on top.
The motor is a sealed electric motor — hermetically sealed windings, so well water never touches the electrical parts — and it's cooled and lubricated by the surrounding water itself. There are no oil changes, no greasing, nothing to service. It runs on a dedicated 240-volt circuit from the breaker panel.
Above the motor sits the pump end: a multistage centrifugal pump. Each stage is one impeller (a spinning disc with curved vanes) followed by a stationary diffuser (a set of fixed vanes shaped like a funnel). Water enters through an intake screen at the bottom of the pump end, the impeller spins and flings it outward, and the diffuser catches that fast-moving water and slows it down in a widening channel — which converts speed into pressure. Then the water flows into the next stage, where another impeller adds more. Each stage adds a little pressure, and a stack of them multiplies into enough head to push water up from hundreds of feet. More stages, more lift.
2-wire vs. 3-wire: where the starting parts live
Submersible motors come in two wiring flavors, and the difference is entirely about where the motor's starting components live:
| 2-wire | 3-wire | |
|---|---|---|
| Starting components | Sealed inside the motor, down the well | In a control box mounted above ground (basement, well house) |
| Wires down the well | 2 conductors + ground | 3 conductors + ground |
| Starting torque | Standard | Higher — better at breaking mineral scale loose |
| If the starter fails | The pump must be pulled up for service | The control box can be tested and repaired at the surface |
A 3-wire control box holds the start capacitor and relay (Franklin Electric's "Quick Disconnect" box is the one you'll see most). The capacitor gives the motor a stronger starting kick, which helps if mineral deposits have gummed up the works. A 2-wire motor has its starting switch sealed in the motor itself — simpler, and nothing extra mounted in the house, but a starting-component failure means pulling the pump. Neither type is "better" in general; it's a trade between serviceability and simplicity.
The check valve: the unsung part
On top of the pump end sits (or immediately follows) a check valve — a one-way valve that lets water go up but not back down. When the pump stops, the check valve keeps the drop pipe full of water and holds the system's pressure. Without it, every start would have to push a whole column of water back up from scratch, and the pump would spin backward as water drained down through it — hard on the motor and the bearings. Install practice calls for the valve within about 25 feet of the pump, below the lowest pumping water level, with additional valves at intervals on very deep sets. Spring-loaded check valves are the norm here; the old flapper style is too slow and causes water hammer on shutdown.
The jet pump: a surface pump with a trick
A jet pump sits above ground — in the basement, a pump house, or an outbuilding — and it's a centrifugal pump with an ejector (jet) assembly bolted on. The ejector is the trick: a nozzle that squeezes part of the pump's own water through a small opening at high speed, into a widening venturi tube. That fast jet of water creates a vacuum behind it, which pulls additional well water up into the flow. Some of the water the pump delivers gets recirculated back down to drive the ejector — the system spends water to move water, which is why jet pumps are less efficient than submersibles.
Jet pumps come in two configurations, split by the 25-foot suction ceiling:
| Shallow-well jet | Deep-well jet | |
|---|---|---|
| Ejector location | Built into the pump itself, above ground | Down in the well, submerged |
| Pipes to the well | One suction pipe | Two pipes (twin-pipe), or one pipe with the casing acting as the second (packer system) |
| Suction lift | Up to 25 feet (vertical lift plus pipe friction) | Water level deeper than 25 feet |
| Where you'll see one | Shallow wells, sand points, cisterns, booster systems | Older drilled wells; wells 4" or larger in diameter |
The deep-well version is the clever bit. Moving the ejector down into the well — typically 10 to 15 feet below the pumping water level — is effectively like burying the pump underground: the suction happens down there, and the surface motor only has to handle the pressure side. The pump sends water down the pressure pipe, the ejector fires it through the venturi, and the vacuum lifts well water up the suction pipe alongside it. Residential deep-well jet packages are rated for pumping water levels roughly into the 100-foot range — but the manufacturer performance tables tell the real story, with gallons per minute falling steeply as the water level drops. Below that range, submersibles take over; it's their natural territory.
Priming, foot valves, and airtight everything
A jet pump cannot pump air. The first time it runs — and any time it loses its water — it must be primed: filled with water by hand through a priming plug. Lose prime, lose water. The foot valve at the bottom of the suction pipe exists to hold prime between runs: it's a check valve with a screen that lets water in but not back out, keeping the pipe full while the pump sits idle.
And one more consequence of pulling by suction: the entire suction side must be airtight. A pinhole air leak on the intake of a submersible is irrelevant (it's underwater). On a jet pump's suction line, the same pinhole lets the pump suck air instead of water, and you get weak flow, sputtering, or no water at all. Jet-pump troubleshooting always starts with looking for air getting in.
Submersible vs. jet: the honest comparison
| Submersible | Jet pump | |
|---|---|---|
| Location | Down the well, submerged | Above ground, in the house or pump house |
| Moves water by | Pushing from below | Pulling by suction (+ venturi assist) |
| Depth range | Any residential depth | Shallow-well: ≤25 ft lift; deep-well: roughly the 100-ft range, declining |
| Noise | Silent — you'll never hear it | Audible hum and vibration in the house |
| Efficiency | Higher (state health-department pump guides note this directly) | Lower — recirculation eats energy |
| Maintenance | Near-zero day to day; everything is down the well | Priming, foot valves, seal/pipe maintenance — but all at the surface |
| When it fails | The crew pulls it up the well — the expensive service call | The motor is right there in front of you |
| Lifespan | 15–25 years is common for a quality unit | Generally shorter, with more interim attention |
The pattern is clear: submersibles win on efficiency, noise, depth, and lifespan; jet pumps win on accessibility — you can put your hands on every moving part without hiring a well crew. That's why new drilled wells are overwhelmingly submersible, while jet pumps persist on shallow wells and sand points where the physics suits them and surface access is genuinely convenient.
Which pump do you have?
You can usually tell without any equipment:
- Submersible: The wellhead in the yard has a sealed well cap and nothing else — no motor, no humming box. Indoors you'll find the pressure tank, the pressure switch, and possibly a 3-wire control box mounted on the wall near the tank. Nothing you can see actually moves.
- Shallow-well jet pump: A motor-and-pump unit sitting in the basement or pump house, one pipe running to the well, and you'll hear it cycle. Often next to the pressure tank.
- Deep-well jet pump: Same surface motor, but two pipes head to the well (or one pipe plus the well casing itself). The ejector is down in the well where you can't see it.
If you're buying a home with a well, figuring out which you have is step one of the buyer's due-diligence guide.
Sizing matters — and it's not about horsepower
Pumps aren't sold as "small, medium, large." An installer matches the pump to two things: the well's depth and water level (which set the total head — the lift plus friction plus the pressure-switch setting) and the household's peak flow rate (gallons per minute when everything runs at once). The motor's horsepower and the number of impeller stages are chosen together against the pump's performance curve.
Why it matters: a pump run far from its designed conditions wears itself out from the inside. A pump oversized for its conditions (big pump, shallow lift) runs in upthrust — the impellers float upward and grind on the diffusers above them. A pump undersized for the job (small pump, deep well) runs in downthrust — the impellers get shoved downward and wear below. Run inside its designed range and the impellers float between the diffusers with minimal wear — which is a big part of why some submersibles last decades and others die young. So when a contractor talks about the "right pump," this is what they mean: the pump whose sweet spot lands on your well's actual conditions, not the biggest motor on the shelf.
When knowing how your pump works won't help
Understanding the machinery is genuinely useful — it makes every contractor conversation sharper. But it's worth being clear about what it can't do for you:
- It won't tell you why the pump is short cycling. That's almost always the pressure tank or switch, not the pump — see the pump and pressure tank troubleshooting guide.
- It won't fix water quality. A pump moves water; it doesn't clean it. Contaminants are a water testing problem, not a pump problem.
- It won't solve a dry well. If the water level has dropped below the pump intake, no pump type helps — the answer is a deeper set, hydrofracturing, or a new well, and that's a contractor conversation.
- It won't make a jet pump work past its physics. A shallow-well jet on a 40-foot water level doesn't need a bigger motor — it needs a different pump. The 25-foot suction ceiling is non-negotiable.
And if the problem is "no water at all," start with the safe homeowner checks — breaker, pressure switch, tank — in the no-water triage wizard before you think about the pump at all.
Frequently asked questions
Why does a submersible pump never need priming?
Because it's submerged. Priming means filling a surface pump's housing and suction line with water so it stops pumping air. A submersible's intake is already under water whenever the pump is properly set below the water level — there's no air to get out. It also can't "lose prime" the way a jet pump can when a foot valve leaks.
Can I replace my jet pump with a submersible?
Usually, yes — and drillers do this conversion routinely on deep-well jet setups, since the well is already deep enough and the two drop pipes come out to make room for one drop pipe plus the submersible's wiring. You'll need a pitless adapter at the wellhead if the old installation doesn't have one, and the wiring run to the well. The payoff is quiet, more efficient operation. Whether it's worth the money on a working system is a math question — see the full ownership economics in the well water system cost and maintenance guide.
What's the difference between 2-wire and 3-wire, in practical terms?
The starting components live in different places. On a 3-wire, they're in a box on your wall — if the pump won't start and the box is the culprit, it's a cheap surface fix. On a 2-wire, they're sealed in the motor — simpler, nothing extra to maintain, but a starter failure means pulling the pump. The 3-wire also starts with more torque, which helps in hard water where mineral scale can grab the works. Either will run for decades in a clean well.
How deep can a deep-well jet pump actually work?
Residential deep-well jet packages are rated for pumping water levels roughly into the 100-foot range, but capacity falls off steeply with depth — a pump that delivers double-digit gallons per minute at 40 feet might manage a trickle at 120. The practical line is drawn by the flow you need: once a jet can't deliver it, a submersible is the answer. Check the specific pump's performance table against your well's pumping water level before assuming it'll do the job.
Does a bigger horsepower pump give me better water pressure?
Not directly — and this is a common money trap. Pressure at your taps is set by the pressure switch (typically 40/60 psi), not by motor size. A bigger pump delivers more flow and handles more lift, but it can't push the system past the switch's cut-out setting. If your pressure is weak, the suspects are usually the switch setting, a clogged filter or screen, or a tired pressure tank — not insufficient horsepower.
Why is my jet pump so loud compared to my neighbor's well?
Your neighbor almost certainly has a submersible. A jet pump's motor spins a few thousand RPM in your basement or pump house — you'll hear it, especially the vibration transmitted through the floor. A submersible spins the same way, but it's a hundred feet underground with a column of water and rock between you and it. If the noise is new or getting worse, though, that's a maintenance flag: worn bearings or a failing motor get louder before they quit.