Well pumps · SQ family
Grundfos SQ vs SQE (constant pressure / CU)
Both are 3-inch Grundfos domestic submersibles with soft start and built-in motor protection. The practical fork is control strategy: SQ runs at a fixed design speed; SQE can vary speed and — with a CU 301/302-class controller, sensor, and small tank — hold a pressure setpoint.
SQ (fixed speed)
- Permanent-magnet motor with built-in frequency converter; runs at essentially one design speed.
- Soft start, dry-run, overload, over/undervoltage, and overtemperature protections are part of the value story.
- Typically paired with a pressure switch and a conventional pressure tank (on/off cycling in a band).
- 2-wire single-phase style install in many cases — no separate motor starter box like classic 3-wire induction motors.
SQE (variable speed) + CU constant pressure
- Same physical family as SQ, plus variable-speed / communication capability.
- CU 301 (common residential constant-pressure package): pressure sensor + small diaphragm tank (often ~2 gal / 8 L) + wall controller. Pump speed tracks demand to hold setpoint.
- CU 300 / CU 302-class units: more advanced monitoring / GO app workflows depending on generation — verify the exact kit for your model year.
- SQE can run without a CU, but you lose the full constant-pressure and diagnostic feature set.
- Tank precharge must match the manufacturer table (often ~70% of setpoint for the small tank). Wrong precharge breaks control.
What you feel in the house
| Topic | SQ + switch / tank | SQE + CU constant pressure |
|---|---|---|
| Pressure feel | Rises and falls in the switch band (e.g. 40/60) | Holds near setpoint while the pump is within its curve |
| Low-flow / night use | Normal short cycles if tank is undersized | CU often uses small-tank boost / on-off at very low flow, then speed control above ~1 gpm |
| Parts / service | Simpler electronics surface | Controller + sensor must be supported by someone who knows the platform |
| Generator / weak supply | Soft start helps both | Soft start helps both; confirm CU and sensor power during outages |
When constant pressure is not magic
If peak fixture demand exceeds what the selected SQE can deliver at the setpoint head, pressure follows the pump curve — the CU cannot invent flow. Size the curve first (GPM and total head), then pick control strategy.
Water quality still matters
Iron, sand, and H₂S affect pump life and what you treat after the well. See iron and rotten-egg / H₂S.
Final pump selection needs your well data and a published performance curve. Talk to a licensed well contractor for design, pull/replace, and code compliance. For product questions, you can also contact R.E. Merrill & Associates.
Hard-water cross-links
- Iron in well water — treatment order after the well can deliver flow
- Rotten-egg / H₂S — smell is not a pump feature
- Size softener by GPG — once pressure and yield are stable