CDBK Variable Frequency Control Cabinet — PID Pressure Regulation & Energy-Saving VFD Technology
The CDBK series variable frequency constant-pressure water supply control cabinet combines AC variable frequency drive technology with microcomputer monitoring to deliver precise pressure regulation across the full pump flow range. By using real-time pipe network pressure as its feedback signal, the cabinet automatically adjusts pump motor speed through PID closed-loop control, maintaining consistent outlet pressure regardless of fluctuating demand — a far more efficient approach than traditional constant-speed pump operation or elevated water tank storage.
How the PID Control Loop Works
A pressure transducer installed on the discharge manifold converts the actual pipe network pressure into an electrical signal fed back to the controller. The controller compares this measured pressure against the user-defined setpoint and adjusts the variable frequency drive output frequency accordingly. When water demand increases and pipe pressure drops, the VFD frequency rises, accelerating the pump motor to restore pressure. When demand decreases, frequency drops and the motor slows, preventing over-pressurization. This continuous automatic adjustment keeps pressure stable within a narrow band and eliminates the pressure spikes and drops associated with on-off pump cycling.
Core Parameters
| Parameter | Value |
| Control voltage | 380 V AC, 3-phase |
| Motor power range | 0.55 – 200 kW |
| Power voltage fluctuation tolerance | Plus or minus 10 percent |
| Ambient temperature | -10 to +40 degrees C (non-freezing) |
| Relative humidity | 20% to 90% (no condensation) |
| Altitude | Below 1000 m |
| Vibration tolerance | Less than 5.9 m/s squared (0.6 G) |
| Inclination tolerance | Less than 5 degrees |
| Design standard | CJ/T 352-2010 (Microcomputer-Controlled Variable Frequency Water Supply Equipment) |
Model Designation
| Code | Meaning |
| CDBK | Chaodun Variable Frequency Control Cabinet |
| 3 | Number of Main Pumps Controlled |
| P | Pressure Control |
| T | Temperature Control |
| K | Unit Interlocking Control |
| 7.5 | Main Pump Power (kW) |
| 2.2 | Auxiliary Pump Power (kW) |
| 1 | Number of Auxiliary Pumps |
Control Functions
Manual Control
Operators can switch to manual mode via the panel, directly starting and stopping individual pumps through dedicated switches. The work selection switch assigns primary and standby pump roles — for a two-pump system, choose “Pump 1 primary, Pump 2 standby” or the reverse. For three-pump systems, options include “Pumps 1 and 2 primary, Pump 3 standby,” and so on.
Automatic Control
In automatic mode, the controller responds to pressure or level signals without operator intervention. When municipal network pressure meets the user requirement, the system remains in standby. When pressure falls below the setpoint, the system automatically starts and enters constant-pressure supply mode.
Remote Monitoring and Control
The cabinet supports remote monitoring, allowing facility managers to observe equipment status and issue control commands from a central control room or off-site location.
Temperature Control
In hot water circulation systems, the cabinet can modulate pump operation based on temperature sensor feedback, maintaining consistent supply temperature alongside pressure regulation.
Automatic Sleep and Wake-Up
When the system detects low-flow or zero-flow conditions — such as during nighttime hours in a residential building — the cabinet automatically shuts down and enters sleep mode, eliminating unnecessary energy consumption. When flow demand resumes, the system wakes and restarts automatically.
Automatic Fault Recovery
After automatic shutdown due to overcurrent, overvoltage, or undervoltage faults, the cabinet can attempt automatic recovery and resume normal operation without manual intervention.
Protection Features
- Primary protection — Automatic protection against motor overload, short circuit, phase loss, and water source interruption.
- Auxiliary protection — Overcurrent, overvoltage, and undervoltage protection for pump motors.
- Standby auto-switchover — If an active pump fails, the standby pump automatically takes over, ensuring uninterrupted water supply.
Pump Rotation and Scheduling
Automatic Pump Addition and Removal
As water demand changes, the cabinet automatically starts or stops additional pumps to match the required flow. When the VFD-driven pump reaches maximum frequency and pressure remains below setpoint, a second pump starts at line frequency. As demand decreases, pumps are stopped in reverse order of startup.
Pump Rotation
The cabinet alternates primary and standby pump roles at programmable intervals (configurable by hour, day, or week). This equalizes running hours across all pumps, preventing the standby unit from sitting idle long enough to develop bearing corrosion or seal degradation.
VFD Pump Cycling
When adding a pump, the first pump starts on VFD, then switches to line frequency while the next pump starts on VFD. When removing pumps, the first-started pump stops first. This VFD-cycling approach ensures each pump experiences soft-start benefits.
Installation and Commissioning
Pre-Installation
Reference the cabinet dimensions to prepare mounting hardware — embedded bolts for concrete floor installations or wall-mount brackets for panel installations. Complete external wiring per the design drawings and remove all dust and debris from inside the cabinet before energizing.
Pre-Energization Checks
- Verify all primary and secondary wiring connections match the wiring diagram.
- Confirm component specifications match the design requirements.
- Check that air switches, contactors, thermal relays, and other components operate freely without binding.
- Inspect for loose screws, foreign objects, or damaged components inside the cabinet.
- Perform insulation resistance testing per applicable electrical codes.
Soft Start Operation
In automatic mode, the VFD or soft starter provides smooth motor acceleration, eliminating the inrush current spike and water hammer associated with direct-on-line starting. This significantly extends the service life of pumps, motors, and piping. For manual starts on larger motors, the autotransformer starter provides reduced-voltage starting with adjustable delay (15 to 120 seconds).
Application Scenarios
Residential and Commercial Building Water Supply
The CDBK cabinet serves residential communities, office buildings, and hotels requiring 24-hour constant-pressure water supply. The elimination of elevated water tanks prevents secondary water contamination and reduces structural load on buildings.
Fire Protection Systems
When integrated with fire pump networks, the cabinet maintains standby pressure in fire piping, ensuring immediate water availability at hydrants and sprinkler heads. The automatic fault switchover provides redundancy critical for life safety systems.
Industrial Process Water
Manufacturing facilities, oil fields, and pipeline pumping stations use the CDBK for constant-pressure industrial water supply and long-distance pipeline boosting. The temperature control function supports hot water circulation and boiler make-up water systems.
Agricultural Irrigation
Sprinkler and drip irrigation stations benefit from the cabinet’s ability to maintain precise pressure across variable field demand, improving irrigation uniformity while reducing energy consumption compared to constant-speed pump operation.
Why Choose Chaodun Pumps
The CDBK variable frequency control cabinet is manufactured in compliance with CJ/T 352-2010 standards and features internationally branded VFD components, programmable logic controllers, and low-voltage electrical components. The digital PID regulation provides precise pressure control with keyboard operation and digital display — fully automatic with no need for continuous operator attendance. The circuit design is straightforward for easy troubleshooting and maintenance.
For system configuration assistance, wiring diagrams, and pump matching recommendations based on your specific flow and pressure requirements, contact our engineering team.