Constant Pressure Well Pump Systems

How a constant pressure system works

A standard well system runs the pump at full speed until the pressure switch reaches cut-out, then shuts it off. The pressure tank feeds the house until pressure falls to cut-in, and the pump starts again. You feel that as a slow sag in pressure, followed by a jump when the pump kicks back on.

A constant pressure system replaces the pressure switch with a pressure sensor and a drive. Franklin Electric's SubDrive manual describes it plainly: by adjusting the motor and pump speed, the drive delivers constant pressure as demand changes. One faucet open, the pump turns slowly. Shower, dishwasher and sprinkler at once, it speeds up. Franklin says pump speed and energy use automatically adjust to water demand.

The drive also ramps the motor up gradually rather than slamming it on at full voltage, and Franklin says that means a cooler motor and lower start-up current.

Who it's for

Go constant pressure if:

• Several people use water at once and you notice pressure swings in the shower.
• You run irrigation, a pool fill or other long draws that keep a standard pump cycling.
• There's no room for a big pressure tank. The system works with a much smaller tank.
• You're replacing a submersible anyway and the extra cost fits the budget.

Stick with a standard pressure switch system if:

• It's a one- or two-person house and pressure swings don't bother you.
• The budget is tight. A conventional pump replacement costs far less (see the table below).
• No local contractor services drives. A drive that fails on a Saturday is a problem if the nearest tech who stocks parts is two counties away.

Options compared

HomeAdvisor's constant pressure range is the same $2,000 to $5,000, against $275 to $1,550 for a submersible pump. Forbes Home also lists constant pressure pumps at $2,000 to $5,000.

Variable frequency drive (VFD) systems

This is what most people mean by a constant pressure well pump. Franklin Electric (SubDrive), Goulds, Grundfos and others sell drive packages. Some drives run a standard submersible motor. Others, like Franklin's SubDrive, are specified for particular motors: the manual says to use it only with Franklin Electric 4-inch submersible motors as listed. Ask the installer whether your existing pump and motor can stay, or whether the job is a full package.

Drives also watch the pump. Franklin's SubDrive flags motor underload, the fault you see when the well is overpumped, and waits before retrying. That's dry-run protection built in.

Cycle stop valves

A cycle stop valve (CSV) is a mechanical valve that sits between the pump and a small tank. When you use a little water, it pinches the flow so the pump keeps running against it instead of filling the tank and shutting off. Pressure stays close to steady during long draws, and there's no electronics to fail. The pump still runs at full speed, so it doesn't save power the way a drive can at low flow.

Pump savers

"Pump saver" usually means a dry-run or underload protector, not a constant pressure device. It shuts the pump off when it senses the well running dry, then retries after a delay. Useful on low-yield wells, but it won't change how your pressure feels.

Numbers that matter

• Starts. Franklin rates its single-phase motors up to 0.75 HP for 300 starts a day and 1 to 5.5 HP motors for 100. A constant pressure system keeps the pump running through long draws instead of stopping and starting.
• Tank pre-charge. On a drive system, Franklin sets the tank's air at 70% of the pressure setting, not the just-below-cut-in setting used on standard systems.
• Tank size. Drive systems can run on a much smaller tank than a standard system. Keep some tank, though. It covers small draws so the pump isn't starting for every glass of water.

What to skip

• Buying a drive to fix a problem it won't fix. Low well yield, a failing pump or a clogged line still cause low pressure with a drive installed.
• Mixing parts without checking compatibility. A drive specified for certain motors may not protect or run a different one properly.
• Paying for "constant pressure" on a booster that's really just a bigger pump. Ask whether there's a variable speed drive in the package.

Install notes

The drive mounts indoors, out of sun and weather, near the panel or pressure tank. Franklin says it should be installed by technically qualified personnel. Expect the contractor to rewire the pump circuit through the drive, install the pressure sensor, set the pre-charge on the tank, and program the pressure you want.

If you run the well from a generator during outages, tell the installer, and read our well pump backup power guide before you buy. Pressure tank pricing for a standard setup is on our well pressure tank cost page, and HomeGuide puts a tank swap at $800 to $1,500.