CU321 Variable Frequency Drive



The Grundfos CU 321 is a constant pressure control system designed for use with 4" larger Grundfos SP pumps and motors. This wall mounted system maintains a constant pressure within the maximum pump performance in spite of varying water consumption.


For 4" or larger wells:

  • Domestic and light commercial water supply
  • Irrigation
  • Livestock watering
  • Water transfer

Features & Benefits

  • Complete solution from one manufacturer
  • Easy setup: Simply select pump model and choose pressure setpoint
  • Four pump choices:  Offered in most popular sizes, both 3 and 5 hp: 15, 25, 40 and 75 gpm
  • Matched pump and motor: 3 hp pump on 3 hp motor and 5 hp pump on 5 hp motor
  • Respects original operating designs; operates pump and motor within its designed rpm and hp ratings
  • Built-in protection features: soft-start, dry run, overload, over/under voltage, sensor alarm
  • Wide voltage range: 3 hp unit; single phase 208-240 VAC (+/- %) - 5 hp input; single or 3-phase 208-240 VAC (+/- %)


  • Complete Solution
  • Easy Set-up
  • Built-In Protection Features




Constant Pressure Systems

Literature Code: L-SP-SL-019
File Size: 2.19 MB


CU 321 Installation & Operation Guide

Literature Code: L-SP-TL-022
File Size: 1.74 MB

Product Guide

Product Guide

Literature Code: L-SQ-PG-001
File Size: 6.95 MB

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