The Well Pump Replacement Guide

How does a jet pump move water?

By cheating. A jet pump does not have the strength to lift a column of water on its own — it tricks the atmosphere into doing the lifting.

The venturi, which is the whole trick

A jet pump is a centrifugal pump — impellers and diffusers — with one extra part bolted on: a jet ejector, which is a matched nozzle and venturi.

High-pressure water is forced through the nozzle. Squeezing it that way makes it accelerate sharply, and as velocity goes up, pressure goes down. That creates a low-pressure zone right at the mouth of the ejector, and well water is pushed in behind it by the ordinary weight of the atmosphere.

Which is why 25 feet is a wall

Atmospheric pressure can only support so tall a column of water, so there is a hard ceiling that no amount of horsepower moves.

• A plain centrifugal pump with no ejector manages roughly 10 to 15 feet of suction lift.
• A shallow-well jet pump puts the ejector in the pump housing, ahead of the impeller, and reaches about 25 feet.
• A shallow-well ejector kit recirculates part of the discharge back through the ejector and can push that to about 28 feet — but delivered volume falls as the distance to water grows. You buy reach with flow.

The deep-well jet: move the ejector down the hole

For water sitting roughly 25 to 100 feet down there is a clever workaround. Instead of trying to create suction at the surface, you send the ejector down the well on two pipes:

• A pressure pipe carrying high-pressure water down to the ejector.
• A suction or return pipe bringing the combined flow back up.

Because the low-pressure zone is now created at depth rather than at the pump, the suction limit stops applying. The jet lifts water to a level the surface pump can finish by ordinary suction. It is a genuinely elegant piece of plumbing and it is why two-pipe well heads exist.

How does a submersible pump move water?

By not bothering with any of that. A submersible sits in the water at the bottom of the well and pushes upward, which sidesteps the atmospheric ceiling completely.

Stages, stacked

Inside the housing is a series of impellers and stationary diffusers. The motor spins the impellers; centrifugal force flings water outward and accelerates it; the diffuser catches that fast-moving water, converts its speed into pressure, and hands it to the next stage.

Each stage adds pressure. Stack enough of them and you can lift from practically any residential depth — multi-stage submersibles routinely serve wells beyond 400 feet. This is the key structural difference between the two families, and it explains the whole market:

Why pushing beats pulling

That last row has a diagnostic consequence worth remembering: on a submersible system, every noise you can hear is coming from the pressure switch and tank. If something sounds different, it is almost never the pump you are hearing.

What is the pressure tank actually doing?

This is the least understood component in a private water system and the one most likely to be quietly destroying your pump right now.

The air spring

A modern pressure tank contains a sealed rubber bladder with compressed air behind it. Water pumped into the tank squeezes that air, and the compressed air is what pushes water to your taps when the pump is off.

The cycle runs on two numbers set at the pressure switch:

• Cut-in — the pressure at which the switch starts the pump. Commonly 30 PSI.
• Cut-out — the pressure at which it stops. Commonly 50 PSI.
• Drawdown — the usable water delivered between those two points, and it is much smaller than people assume. Only about 25 to 30 percent of a tank's total volume is usable. A healthy 20-gallon captive-air tank delivers roughly 5 to 6 gallons.

The 2 PSI gap, which nobody explains

The tank's air pre-charge is set 2 PSI below cut-in — 28 PSI on a 30/50 switch, 38 PSI on a 40/60. That gap looks arbitrary. It is not.

Checking it takes a tire gauge on the Schrader valve at the top of the tank, with the system depressurized. Pre-charge drops over time even on a healthy tank, because air slowly permeates through the rubber and the valve itself can seep.

What "waterlogged" actually means

When the bladder fails, water fills the entire tank and the air cushion is gone. There is nothing left to store energy, so drawdown drops to almost nothing.

The consequence is mechanical and brutal. The pump satisfies cut-out in seconds because there is no volume to fill, then pressure collapses back to cut-in seconds later, and it starts again. Short-cycling.

Two causes that are not the bladder

Worth knowing so you do not replace a good tank:

• Lost pre-charge with an intact bladder. Air permeates slowly through rubber and leaks at the valve. The fix is adding air, not a new tank.
• A tank too small for the pump's flow rate. Perfect bladder, correct pre-charge, still short-cycles — because the drawdown volume is too small for how fast the pump fills it. This is a sizing error, and it usually dates back to the original install.

A leaking check valve down in the well can also mimic waterlogging closely, which is one reason the cheapest-cause-first diagnostic ladder is worth walking in order rather than guessing.

How is a replacement pump sized?

Two numbers define every pump on the market, and neither of them is "how deep is the well."

Total dynamic head — the number that is not well depth

TDH is the total resistance the pump has to overcome, expressed in feet. It adds up four things:

1. The pumping water level — how far down the water sits while the pump is running.
2. The vertical rise from there to the pressure tank.
3. Friction losses in the pipe and fittings.
4. The tank operating pressure, converted to feet. One PSI is about 2.31 feet of head.

And the distinction that catches almost everyone: what matters is the pumping level, not the drilled depth. A 300-foot well with water standing at 50 feet is an easier job than a 200-foot well with water at 180.

Gallons per minute, from peak demand

Flow is sized from simultaneous peak use, not from average daily consumption. The common rule of thumb is 1 GPM per fixture. A typical three-bedroom, two-bath house has 10 to 12 fixtures and wants roughly 8 to 12 GPM; most homes land in a 6 to 12 GPM band.

Well yield, which overrides both

Here is the constraint that beats every other number on this page.

Oversizing is a genuine failure mode, not a harmless margin. An oversized pump on a low-yield well pulls the water level down past its own intake, runs dry, and short-cycles against the pressure tank — dry running and rapid cycling being the two most destructive things that can happen to a pump, arriving together.

If yield is the binding constraint rather than the pump, the eventual answers are storage, hydrofracturing, deepening or a new well — in roughly that order of cost, and none of them fixed by a larger motor.

Treat this table as a sanity check on a quote, never as the basis for one. Real selection comes from plotting your GPM and TDH against a specific pump's performance curve — depth alone is not sufficient, and a contractor who sizes from depth alone is guessing.

What are the parts of a well, top to bottom?

Useful vocabulary, because it is hard to evaluate a quote for components you cannot name. Here they are in the order a technician meets them.

The torque arrestor is the one worth asking about specifically. It is a cheap rubber part that prevents the most avoidable form of premature failure — a pump that has spent years scraping its own wire against a steel casing.

What are the early warning signs?

These arrive weeks or months before anything dramatic. All of them justify a scheduled service call rather than an emergency one, which is also materially cheaper.

• Cycle frequency changing. The earliest measurable signal, and you need no tools — just a watch. Baseline is 6 to 8 starts an hour under moderate use. Anything faster, especially when drawing small amounts of water, points at pre-charge loss before it becomes full waterlogging.
• Sputtering or spitting air at the taps. Air is entering the system. Usual suspects: a falling water level pulling the pump toward its intake, a suction leak on a jet pump, or a failing check valve.
• The sound changing. A jet pump running rougher or louder. On a submersible, new noise at the tank or switch — because that is where you hear a submersible system.
• Cloudy, sandy or gritty water. Suggests a failing screen or a pump set too low and drawing sediment. Sediment abrades impellers and seals, so this one is actively shortening the pump's life while you watch it.
• Pressure sagging when a second fixture opens. Low pressure upstairs, not being able to run two things at once, or a pump that runs and runs without reaching cut-out — all say the pump is losing ground against demand.
• A rising electric bill with no change in habits. A pump running longer or more often to deliver the same water.

When something does need diagnosing, work up from the cheapest possible cause — the cost guide's diagnostic ladder starts at a free breaker check and a $25 part, and a fair number of "dead pumps" never get past rung two.

Can you replace a well pump yourself?

In Texas and Florida, generally no — pump installation on a private well is licensed work in both states, and the license covers pump work specifically rather than only drilling. The registries are public and looking a contractor up takes two minutes; the cost guide has the statutes and the lookup detail.

Setting the law aside, the physical reality is worth stating plainly. A drop pipe full of water at 300 feet is several hundred pounds suspended over an open hole in the ground. If it gets away from you, the pump goes to the bottom of the well and recovering it — a "fishing" job — can cost more than the pump did.

There is a real difference between swapping an accessible shallow jet pump in a well house and pulling a submersible, and it is not unreasonable for a competent homeowner to think about the first. Check your state and county rules before you touch either, because doing unlicensed well work is its own problem regardless of how it turns out.

How often should you test the water?

Annually, at minimum — total coliform bacteria, nitrates, total dissolved solids and pH, per EPA and CDC guidance, plus anything known to be a local issue such as arsenic or radon. Your county health department can tell you what those are. Every three to five years, run a broader panel including metals and minerals.

Test off-schedule when any of these happen:

• Someone in the household becomes pregnant, or a young child moves in.
• Taste, smell or appearance changes at all.
• Any repair or replacement opened the well system — a pump pull included.
• After flooding, or any significant environmental change nearby.
• Known water problems appear in the area.
• You have just bought the property. Test immediately, to establish a baseline you can compare against later.

One result deserves a specific reaction rather than a general one. A coliform or nitrate hit on a rural property with its own septic system is a septic question before it is a well question — a failing drain field near a well shows up in the water long before it shows up in the yard. Test the water, then look at the field.

The one thing to take away

The pump gets the blame and the tank does the damage.

A pump is a fairly simple machine that lasts a decade and a half if you let it work the way it was designed to — starting a handful of times an hour and running for a while each time. The most common way to shorten that life by ten years is a failed or wrongly pre-charged pressure tank that has it starting and stopping every few seconds, all day, for two years, while the household notices nothing at all.

So: check the pre-charge against the switch setting, press the Schrader valve once a year, count cycles once a season. Then when something does go wrong, walk the diagnostic ladder from the cheap end instead of the expensive one.