Two Ways to Get Constant Pressure From a Well Pump

A constant pressure well pump system keeps delivery pressure steadier as water demand changes. It does not mean unlimited flow, identical pressure at every faucet, or a pump that runs continuously.

Two approaches can provide that result: changing pump speed with an electronic drive, or regulating a fixed-speed pump with a purpose-designed control valve. The useful comparison is how each fits the existing pump, motor, piping and pressure tank—not simply which can be set to the desired PSI.

Constant pressure is the result; variable speed is one method

A conventional pressure-switch system lets pressure move between its start and stop settings as water leaves and refills the pressure tank. Constant-pressure control instead regulates pressure during active demand, within the system’s operating limits.

Variable-frequency drive

A variable-frequency drive, or VFD, receives feedback from a pressure sensor or transducer and changes motor speed. Opening additional outlets causes the controller to increase speed; reducing demand allows it to slow down, subject to its operating limits. Xylem describes this speed-regulation principle for its residential constant-pressure systems.

The drive, motor and pump must be compatible. Do not assume that every existing single-phase well motor accepts any VFD. Franklin’s SubDrive Connect range supports specified two-wire, three-wire and three-phase applications, but that versatility belongs to the particular product range—not to all drives. Verify the exact motor and controller combination before ordering. Franklin Electric’s product information also identifies available dry-run, overload and other protections.

For detailed drive selection, electrical compatibility and operating limits, see our guide to variable-speed well pumps.

Fixed-speed pump with a constant-pressure valve

A purpose-designed valve such as a Cycle Stop Valve regulates downstream pressure by restricting discharge flow as demand falls. The motor still runs at fixed speed. The valve retains a minimum flow path; when demand stops, that flow fills the pressure tank until the pressure switch stops the pump. Regulation applies over a flow range, not at every possible demand. Cycle Stop Valves’ operating description explains the minimum-flow and tank-fill functions.

This is not simply a standard pressure-reducing valve added anywhere in the plumbing. For the CSV1A, the manufacturer specifies installation before all outlets, with the tank and pressure switch downstream. It also warns that the valve creates upstream backpressure and that piping between pump and valve must be rated for it. The installation instructions make those requirements explicit.

Compare the retrofit requirements

Question	VFD approach	Constant-pressure valve approach
How is pressure regulated?	Pressure feedback changes motor speed	A valve restricts discharge while motor speed stays fixed
What is the main compatibility check?	Exact drive–motor pairing, wiring and approved speed range	Pump suitability, valve operating range and upstream pressure ratings
What controls require attention?	Sensor placement, response settings and low-flow shutdown	Valve setting, pressure-switch settings and tank-fill flow
Can the existing tank remain?	Possibly; follow the controller’s tank requirements	Possibly; coordinate tank size, precharge, valve setting and switch settings

A valve-based retrofit is worth evaluating when the existing fixed-speed pump has suitable capacity and pressure ratings. A VFD is worth evaluating when a compatible pump-and-motor combination and electronic regulation suit the job. For either option, ask who can service the controls and obtain replacement parts locally.

Neither pressure setting proves hydraulic suitability. For a valve system, have the installer verify both the maximum upstream pressure and whether the valve’s minimum flow is suitable for the pump and motor. A safe pressure at the downstream gauge does not establish a safe pressure between the pump and valve.

Check flow at the required head—not just horsepower

The pump must supply the required gallons per minute at the total dynamic head, or TDH, of the installation. For a submersible well supplying a pressurized system, a useful calculation is:

TDH = vertical lift from pumping water level to the delivery point + required pressure head + pipe, fitting and equipment losses.

Use the water level while pumping, not just the drilled depth or resting water level. Include treatment equipment and the control valve, where fitted, at the intended flow. Grundfos’ pump-selection training explains these head components and the conversion of approximately 2.31 feet of water head per PSI.

For example, assume:

• Pumping water level is 120 feet below the pressure-control point.
• Required pressure there is 50 PSI.
• Calculated losses to that point are 20 feet at 10 GPM, including any valve loss.

The duty is approximately 10 GPM at 256 feet TDH: 120 + (50 × 2.31) + 20. Those are illustrative inputs, not a household sizing recommendation.

Ask the supplier to show that duty on the proposed pump curve. For a variable-speed package, check performance within its approved speed range. For a valve-controlled system, also check upstream pressure at low flow and the valve’s permitted pressure differential. The valve manufacturer’s technical guidance specifically identifies high differential pressure as a design concern.

A steady pressure reading near the tank also cannot erase losses farther downstream. An upstairs shower or a long irrigation branch can have lower pressure because of elevation and friction, especially as flow increases.

Keep the pressure tank—and use the right settings

Constant pressure does not ordinarily mean tankless. Franklin states that SubDrive Connect works with small pressure tanks or existing larger tanks; the CSV1A instructions likewise require a downstream diaphragm tank. The required size and precharge depend on the control method and model.

Do not automatically carry over a conventional pressure-switch precharge rule to a VFD. For example, the 2019 SubDrive Connect manual specifies precharge as a percentage of target pressure, while the CSV1A instructions relate it to pressure-switch cut-in. Those are different control arrangements. Use the current instructions for the exact equipment, and check precharge only with the pump disabled and the water side depressurized. Franklin’s model-specific manual details that procedure and its tank requirements.

Separate a control upgrade from a supply problem

Pressure control cannot make the well replenish faster. If demand exceeds sustainable yield long enough to exhaust available stored water, changing the controller does not resolve the shortage.

For a low-yield well, compare storage and demand management before buying a larger pump. Penn State Extension describes intermediate storage: the well fills a nonpressurized reservoir, and a separate pressure pump supplies the building. Constant-pressure delivery may be useful on that reservoir’s discharge side.

A useful quote should document demand and required pressure at a stated location, pumping water level, well yield, TDH, the pump curve, exact equipment models, component compatibility, tank settings and protective provisions. For a valve retrofit, insist on the upstream-pressure check; for a VFD retrofit, insist on confirmation of the motor–drive pairing.

If the reason for upgrading is newly weak pressure, first trace the existing well-pressure problem. A restriction, leak or declining water level needs diagnosis, not just a different pressure setting. Leave electrical testing and internal drive work to qualified personnel: a drive can retain hazardous voltage after power is disconnected, as the SubDrive Connect manual warns.