Best Constant Pressure Well Pump Systems (2026)

Plumbing Picks is reader-supported. As an Amazon Associate, we earn from qualifying purchases at no extra cost to you.

Quick answer from a licensed plumber: For a submersible well, buy a matched set from a well-pump dealer and have a licensed pro install it: Franklin MonoDrive or 2-wire SubDrive if you keep your Franklin motor, or a Grundfos SQE with a CU 301 for a new small well. The Goulds AQUAVAR SOLO2 1AS15 fits a single-phase CentriPro or Grundfos motor, and its 3AS models run three-phase motors on single-phase power. If your pump sits above ground on a well whose water level stays within 26 feet below the pump while it runs, the Aquastrong Smart 45 is the one sold by its maker.

Our pick depends on your well. Franklin motor: a Franklin MonoDrive or 2-wire SubDrive from a well-pump dealer. Single-phase CentriPro or Grundfos motor: the Goulds AQUAVAR SOLO2 1AS15 (sold by a third-party seller). Check the Goulds AQUAVAR SOLO2 1AS15 on Amazon New small well: a Grundfos SQE with its control unit, from a dealer. Above-ground pump on a shallow well: the Aquastrong Smart 45. Check the Aquastrong Smart 45 on Amazon

A pressure switch runs the pump at full speed until the tank fills. A constant pressure system reads the pressure with a transducer and changes the motor speed, so the tap pressure stays put while you run a shower and the dishwasher together. It is not one pump you buy off a shelf. It is a matched set of a drive, a transducer, a small tank and a pump and motor the maker approves. Most of it goes down a well, so we lay out what Franklin, Grundfos and Goulds publish, plus the one above-ground pump we can link.

What a Constant Pressure System Needs

A variable-speed controller. A drive such as Franklin’s SubDrive or MonoDrive, the Goulds AQUAVAR SOLO2, or the drive built into a Grundfos SQE pump.
A pressure transducer. The drive reads it. Franklin ships a sensor with the drive, Goulds lists the transducer with its controller, and Goulds says to keep transducer wires 12 inches from power wires.
A small pressure tank. The tank only smooths out the drive. See the best well pressure tank picks.
A pump and motor the maker approves. Franklin, Grundfos and Goulds each name the motors and pumps their controller works with. Using anything else can damage the equipment and void the warranty.

Constant Pressure Well Systems Compared

System	Fits	Power in	Matching rule	Where to buy
Franklin MonoDrive / 2-wire SubDrive	Existing Franklin 2- or 3-wire motor, 1/2–1 hp (MonoDriveXT to 2 hp; UT2W to 1 1/2 hp)	Single-phase: MonoDrive 208/230 V; UT2W 115 V (1/2 hp) or 230 V	Franklin motors only; 2-wire motors need at least a 20-gallon tank	Well-pump dealer
Grundfos SQE + CU 301	New SQE pump, 3-inch borehole and up	1 × 200–240 V; 1 × 100–115 V for the 0.7 kW motor only (international booklet)	SQE pump only; never an outside drive or a capacitor box	Well-pump dealer
Goulds AQUAVAR SOLO2 (1AS15)	Single-phase CentriPro or Grundfos motor, 1/2–2 hp (1AS15); three-phase motors (3AS models)	196–265 V, no GFCI	Motor overload set from motor amps; wire per Goulds table	Amazon (1AS15, third-party seller) or well-pump dealer
Aquastrong Smart 45	Shallow well, above ground; water level within 26 ft below the pump while it runs	115 V plug-in	Well setpoint 44 psi maximum	Amazon, sold by Aquastrong

Details come from the Franklin, Grundfos, Goulds and Aquastrong documents listed under Sources. We link two of the four. When we checked on September 28, 2026, we found no Franklin SubDrive or MonoDrive listing on Amazon, and the only Grundfos CU 301 listing was a third-party seller with 2 left, so we do not link those; a well-pump dealer can supply them and confirm the exact match. The Goulds AQUAVAR SOLO2 1AS15 was listed in stock on Amazon, but sold by a third-party seller (eFaucets) and not by Goulds or Amazon, with 13 left. The Aquastrong was listed in stock on Amazon, sold by Aquastrong and shipped by Amazon. For a shallow well without a drive, see our best shallow well pump picks.

Best for Retrofitting a Standard Well

Franklin Electric MonoDrive and 2-Wire SubDrive Controllers

MonoDrive: 3-wire motors, 1/2 to 1 hp (MonoDriveXT to 2 hp) · 2-wire: SubDrive2W in Franklin’s brochure (1/2–1 hp, 207–260 V in); Franklin’s 2023 AIM lists the SubDrive Utility UT2W (1/2 hp at 115 V, up to 1 1/2 hp at 230 V) · MonoDrive 208/230 V in · 25–80 psi, preset 50 psi · pressure sensor included · UL and cUL listed

Franklin’s controllers are the retrofit route. Franklin says MonoDrive converts a conventional 1/2 to 2 hp system to constant pressure by replacing the 3-wire control box and pressure switch, and the 2-wire SubDrive does it for a 1/2, 3/4 or 1 hp two-wire system by replacing only the pressure switch. The drive holds the pressure you set by changing motor speed, with a soft start. Franklin’s own note on the SubDrive2W is worth reading: its maximum pump output is similar to what you get with a pressure switch, so you choose the pump the same way. A drive gives steadier pressure, not more water. Franklin’s 2023 AIM manual lists the current 2-wire drive as the SubDrive Utility UT2W, so ask the dealer which 2-wire model they stock.

The matching rules are strict. Franklin’s AIM manual says its single-phase 2- and 3-wire motors can only be used with the appropriate Franklin constant pressure controller, and that the warranty on its 2-wire motors is void on a non-Franklin drive. The MonoDrive sheet pairs each size with a specific motor series: 214505 for 1/2 hp, 214507 for 3/4 hp, 214508 for 1 hp. MonoDrive input is single-phase 208/230 V. The output-wire range is #6 to #14 on the NEMA 3R model, and Franklin says to use 75°C copper and never aluminum with SubDrive. Franklin tells you to keep motor cable under 1,000 feet for best results. It needs only a small tank: the pre-charge for the factory 50 psi setting is 35 psi, and 2-wire motors need at least 20 gallons.

Replaces the pressure switch or control box on an existing Franklin system (Franklin)
Adjustable 25–80 psi, factory preset 50 psi
Works with a small tank or an existing larger one, per Franklin
Soft start with underload, locked-pump and undervoltage protection built in

Only for the Franklin motor series it lists; Franklin voids its 2-wire motor warranty on other drives
We found no Franklin SubDrive or MonoDrive listing on Amazon, so it comes through a well-pump dealer
2-wire motors need a tank of at least 20 gallons, so the small-tank saving is smaller
A drive adds electronics that must be sized, wired and set up correctly

Verdict: The route if you already have a Franklin motor and want constant pressure without replacing the pump. A licensed pro should size and wire it.

Best Complete Package for a Small Well

Grundfos SQE Pump with CU 301 Controller

SQE 1, 2, 3, 5 and 7 m³/h models · MSE 3 permanent magnet motor with built-in frequency converter · 1 × 200–240 V, or 1 × 100–115 V for the smallest 0.7 kW motor, 50/60 Hz · 76 mm (3 in) minimum borehole · up to 150 m below static level · CU 301, 0–6 bar sensor and 8-litre tank

Grundfos builds the variable-speed drive into the pump. SQE pumps use a single-phase motor with a built-in frequency converter and soft start, and Grundfos says the CU 301 control unit is developed for constant-pressure jobs. Grundfos’ residential diagram shows the SQE pump, its cable, an 8-litre tank, the CU 301 and a 0–6 bar pressure sensor. The CU 301 talks to the pump through the power cable, so no extra cable runs down the well. At very low flow, under about 0.18 m³/h (about 0.8 GPM, our arithmetic), the pump cycles on and off 0.5 bar either side of the setpoint. The pump fits a 3-inch borehole, and the largest size in the range is labelled 7 m³/h, about 31 GPM (our arithmetic).

Wire and voltage rules are Grundfos’ own. Grundfos’ international booklet lists 1 × 200–240 V, plus a 1 × 100–115 V version of its smallest 0.7 kW motor (confirm the US model with the dealer), and the voltage at the motor terminals must stay within −10% to +6% of nominal. Grundfos gives maximum drop-cable lengths at 5% voltage drop: for its largest 1.85 kW motor at 240 V, 37 m (about 121 ft, our arithmetic) on 1.5 mm² cable and 150 m (about 492 ft) on 6 mm². Grundfos says an authorised electrician must make the connection, and that the pump must never be connected to an external frequency converter or to a capacitor box. One conflict: the data booklet names the CU 300 and CU 301, while the installation instructions say CU 302. Confirm the control unit for your pump with a Grundfos dealer.

Pump, CU 301, sensor and tank are designed as one constant-pressure system (Grundfos)
Fits a 76 mm (3 in) borehole
Dry-running, over- and undervoltage, overload and overtemperature protection built in
Grundfos gives cable-length tables so wire is sized to the motor

The Grundfos documents we opened are the international 50/60 Hz editions in metric units; ask the dealer for the US data sheet before sizing
Data booklet and installation instructions name different control units (CU 301 vs CU 302)
The only Amazon listing we found for a CU 301 was a third-party seller with 2 left, and no SQE pump listing, so a dealer is the way to buy
Replaces the pump; it is not an add-on for a standard pump

Verdict: The neat all-in-one for a new or replacement small well with a 3-inch casing, bought and installed through a Grundfos dealer.

Best for CentriPro or Three-Phase Motors

Goulds AQUAVAR SOLO2 Constant Pressure Controller

1AS15 for single-phase 2- or 3-wire motors · 3AS20, 3AS30 and 3AS50 for three-phase motors from single-phase 230 V · input 196–265 V · setpoint 20 psi up to 85 psi (100 psi transducer) · NEMA 3R, −4°F to 122°F

The SOLO2 is a controller only. Goulds’ manual lists the controller with its transducer and transducer wire; the Amazon listing does not say, so confirm the transducer is in the box before you order. Goulds pairs it with a submersible motor and pump and a pressure transducer, and its manual says to use it alongside the pump manual. The 1AS15 runs single-phase 2- or 3-wire motors, and the 3AS models run three-phase motors from a single-phase supply, which is how a three-phase pump works on residential power. Goulds lists service-factor amps for CentriPro, Franklin and Grundfos motors and has you set the overload dial from the motor’s amps. Franklin’s AIM manual, though, says its single-phase 2- and 3-wire motors can only be used with a Franklin constant pressure controller, and that a Franklin 2-wire motor on a non-Franklin drive voids the warranty. So with a Franklin motor, use a Franklin drive; the 1AS15 makes most sense with a CentriPro or Grundfos single-phase motor. The controller is rated NEMA 3R and Goulds says it may be mounted at the wellhead.

This manual is the most detailed on the rules. The input must be 196 to 265 V, and Goulds says not to use a GFCI on it because it causes nuisance trips. Wire is copper rated 75°C, sized in Goulds’ tables at a 5% drop. For a 1 hp motor on a single-phase supply, Goulds lists 226 ft of #14, 360 ft of #12 and 571 ft of #10 from the service entrance to the controller, and the controller-to-motor run is budgeted separately. Underwater splices must use waterproof heat-shrink kits, and Goulds says vinyl tape is not acceptable and failing to use one voids the warranty. Transducer wires must stay 12 inches from power wires, and no valve or filter may sit between the transducer and the pump. Tank pre-charge is 20 psi below the setpoint for the 5 psi drop setting and 30 psi below for the 20 psi setting. Goulds calls for a relief valve piped to a drain.

Detailed wire, breaker, generator and tank tables in one manual (Goulds)
Choice of single-phase-motor and three-phase-motor models
Setpoint adjustable from 20 psi up to 85 psi with the 100 psi transducer
Outdoor-rated NEMA 3R enclosure that can mount at the wellhead

A controller only: the pump and motor are matched separately from Goulds’ tables
Cannot run on a GFCI-protected circuit, and needs a 196–265 V supply
The Amazon listing is from a third-party seller (eFaucets), not Goulds; a well-pump dealer can also supply and confirm the match
Not the retrofit for a Franklin motor: Franklin says its single-phase motors can only be used with a Franklin controller

Verdict: The choice for a single-phase CentriPro or Grundfos motor, a three-phase motor on single-phase power, or a system a pro wants to size from published wire and tank tables. The button links the 1AS15 for single-phase motors; a three-phase motor needs a 3AS model.

Check the Goulds AQUAVAR SOLO2 1AS15 on Amazon

Best Above-Ground Option (Shallow Wells Only)

Aquastrong Smart 45 Booster Pump (115 V)

115 V, 60 Hz, 3/4 hp, 6.8 A max (nameplate) · 1-inch NPT inlet and outlet · 22–80 psi, preset 44 psi · max 1,500 GPH and 150 ft of head · 26 ft maximum suction lift · water 32–175°F · 55 dB(A) · IPX5 · 24-month warranty

This is the one pump here that is not a submersible system. The Smart 45 is a self-priming, variable-speed pump with a built-in tank, pressure sensor and check valve. It sits above ground and pulls water by suction, so it can serve a shallow well only, and Aquastrong’s manual sets the maximum suction lift at 26 feet. Suction lift is measured from the pump down to the water level while it is pumping, not the resting level (our note), and Aquastrong adds a minimum outlet pipe resistance once lift passes about 20 feet (6 m). It cannot replace a submersible pump in a deeper well. Aquastrong lists 1,500 GPH as its maximum flow, which is 25 GPM (our arithmetic), and its manual has no flow-by-lift table, so that figure is the pump at its best.

Aquastrong’s manual is specific about wells. For a well, the pressure setpoint should not go above 44 psi, and the difference between inlet and outlet pressure must not exceed 51 psi. Use a foot valve with a strainer, keep the inlet pipe under water by at least 1.64 feet, and put a filter on the inlet if the water can carry sand or gravel. The tank pre-charge is 18 psi, and priming takes at least 1.2 litres of water in the pump housing. It plugs into a standard 115 V outlet, but Aquastrong says the pump must be grounded, and installs must follow local code. Ask a plumber if you are unsure about the suction line.

Constant pressure from an above-ground pump with a tank and sensor built in (Aquastrong)
Listed for shallow wells to 26 feet of suction lift
Dry-run, overheating, blockage and sensor-fault protection, per the manual
24-month warranty from the maker

Not for deep wells or submersible replacement: suction lift stops at 26 ft
Well setpoint is capped at 44 psi, lower than a 40/60 switch system
No flow-by-lift table in the manual we opened
55 dB(A) in typical use, per Aquastrong

Verdict: The pick if your pump sits above ground on a well whose water level stays within 26 feet below the pump while it runs, and you want steady pressure without a big tank.

Check the Aquastrong Smart 45 on Amazon

I send an occasional note when a new guide goes up — repairs worth doing yourself, and the parts that actually last. No spam, no course funnel; written by a licensed Georgia plumber.

Before You Buy

Read the motor nameplate. Note horsepower, voltage, 2-wire or 3-wire, and the motor series. Every maker on this page ties its controller to specific motors.
Match the voltage. Franklin’s MonoDrive takes single-phase 208/230 V, Grundfos’ international data booklet lists 1 × 200–240 V, or 1 × 100–115 V for its smallest 0.7 kW motor (confirm the US model with the dealer), and Goulds needs 196–265 V. Check the voltage at the panel with a meter.
Size the wire. Use the maker’s table for your motor and run length. Franklin says 75°C copper and never aluminum on a SubDrive, and Goulds gives lengths at a 5% drop. Longer runs need heavier wire. Our submersible well pump guide covers cable sizing for standard pumps.
Plan the tank. Set the pre-charge to the maker’s rule, always with the tank empty. Franklin gives 35 psi for its 50 psi setting. See the tank size and drawdown chart.
Add a relief valve and a gauge. Goulds calls for a relief valve piped to a drain and a gauge to set pressure. Our well pressure gauge picks help you check the setting.

When a Standard Pressure Switch System Is Fine

Most wells run fine on a pressure switch and a properly sized tank. That is our view, not a maker claim. If the pump has years left and the 30-to-50 or 40-to-60 swing does not bother you, keep it. A switch system is simpler to diagnose and any plumber can replace the parts. A drive adds a controller, a transducer and a matching rule to follow. Franklin says a SubDrive pumps more or less water as you need it instead of draining and filling a large tank, so a drive makes sense when the swing bothers you, when short cycling is wearing the pump, or when you are replacing the pump and want the smaller tank. Otherwise, start with the pressure switch guide and the tank picks. If your well pump is fine but house pressure is low, a booster pump is another route.

Who Should Install It

On a submersible well, hire a licensed pro. Grundfos says an authorised electrician must make the connection, Goulds says a qualified technician must do all electrical work to the National Electrical Code, and Red Lion says to employ a licensed electrician or water systems contractor. The work includes splicing the motor leads with a heat-shrink kit, pulling the pump on its pipe and setting the drive. Goulds and Franklin both say not to put their drives on a GFCI, which Goulds says causes nuisance trips. That differs from a standard pump, so if your inspector calls for ground-fault protection, ask the drive maker which device works with it. Ask your installer to put the motor amps, drop cable size and drive settings on the tank label for the next person. The Aquastrong is a plug-in above-ground pump, but its suction line still has to be airtight and its foot valve in the water.

FAQ

What does a constant pressure well system need?

Four things: a variable-speed drive or controller, a pressure transducer, a small pressure tank, and a pump and motor the maker approves for that drive. Franklin, Grundfos and Goulds each publish which motors and pumps go with which controller. A pressure switch does not do this job; the drive reads a transducer and changes motor speed.

Can I add constant pressure to my existing submersible pump?

Sometimes. Franklin says its single-phase 2- and 3-wire motors can only be used with the appropriate Franklin controller, so a Franklin motor needs a Franklin drive. Goulds lists service-factor amps for CentriPro, Franklin and Grundfos motors, but Franklin voids its 2-wire warranty on other drives. A Grundfos SQE pump has the drive built in, so it replaces the pump. Read the motor nameplate first, and have a licensed pro confirm the match.

Do I still need a pressure tank?

Yes, a small one. Franklin says a SubDrive needs only a small tank, but 2-wire motors need at least 20 gallons. Grundfos draws its system with an 8-litre tank. Goulds gives a minimum tank by pump flow and a pre-charge rule: 20 psi below the setpoint for the 5 psi drop setting. See our tank size and drawdown chart.

Is constant pressure worth it, or is a pressure switch fine?

Franklin says a SubDrive pumps more or less water as you need it, instead of draining and filling a large tank. In our view, a standard switch and tank are fine if the pump runs steadily, the pressure swing does not bother you, and you want the simplest system to repair. A drive earns its cost when shower pressure swings annoy you, or when you want a smaller tank or a gentler start on a long cable. See 30/50 vs 40/60.

Is this a do-it-yourself job?

On a submersible well, hire a licensed pro. Grundfos says an authorised electrician must make the electrical connection, Goulds says all electrical work must be done by a qualified technician to the National Electrical Code, and Red Lion says to employ a licensed electrician or water systems contractor. Pulling a pump on a drop pipe is also heavy, risky work. Rules for well work vary by state, so check yours. The above-ground Aquastrong is the only unit here a careful homeowner might set up.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. Every size, rating and spec on this page comes from the manufacturer documents listed below, which we opened and read, or from the Amazon listing we link; nothing here comes from hands-on testing. Of the two linked products, the Aquastrong was listed in stock on Amazon and sold by its maker, and the Goulds controller was listed in stock with 13 left but sold by a third-party seller, when we checked on September 28, 2026. Where a link goes to Amazon we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.

Sources

Bottom Line

Constant pressure is a matched system, not a single pump. Read the motor nameplate, then follow the maker’s table for voltage, wire size and tank. Franklin fits an existing Franklin motor, Grundfos SQE is the all-in-one for a new small well, and the Goulds AQUAVAR SOLO2 covers CentriPro or Grundfos single-phase motors and three-phase motors. On a submersible well, the install is a licensed pro’s job. If your existing pressure-switch system works and the swing does not bother you, it is fine to keep it.