CDWG Non-Negative Pressure Water Supply Unit — Installation & Commissioning Guide
The CDWG non-negative pressure water supply unit leverages municipal pipe network pressure as its intake source, stacking that baseline pressure through variable frequency drive technology to deliver consistent building water service. This guide covers the complete installation, wiring, and commissioning workflow so system integrators and maintenance engineers can verify each step before handing the unit over to facility operations.
Pre-Installation Checklist
Before the unit arrives on site, confirm the following conditions are met:
- Municipal network inlet pressure at or above 0.15 MPa — this minimum ensures the non-negative pressure stacking effect functions as designed.
- Clearance space of at least 600 mm on all four sides for routine maintenance access.
- Media temperature at or below 40 °C and ambient room temperature at or below 40 °C.
- Control cabinet power phase and grounding verified against local electrical codes.
Installation Procedure
Step 1 — Leveling and Base Preparation
Place the unit on a firm, level surface. Use vibration isolators to achieve horizontal alignment within 2 mm per meter. The equipment base design eliminates the need for embedded anchor bolts, which simplifies retrofit installations in existing mechanical rooms.
Step 2 — Flexible Pipe Connections
Connect the inlet and outlet piping using flexible rubber joints. This isolates pipe stress from the equipment body — rigid connections can transmit thermal expansion forces into the pump casing and cause premature seal wear. Any bypass piping must be independently supported; do not allow bypass pipe weight to rest on the unit.
Step 3 — Control Cabinet Wiring
Position the control cabinet junction box facing outward for service access. Route signal cables and power cables through separate conduits and secure them at regular intervals. Ground resistance must measure 4 ohms or less. This separation prevents electromagnetic interference from the VFD from corrupting pressure sensor signals.
Step 4 — Pressure Tank Pre-Charge
Set the pressure vessel pre-charge pressure to 70–80% of the system working pressure. For a system targeting 0.4 MPa, the pre-charge should read approximately 0.28–0.32 MPa. This ratio ensures the bladder absorbs pump start-stop cycling without short-cycling the drive.
Step 5 — HMI Configuration
Through the human-machine interface, set the target pressure — typically between 0.3 and 0.6 MPa depending on building height — and configure the pump rotation logic. Verify the negative pressure eliminator valve moves freely before startup. Open the municipal inlet valve and confirm water reaches the unit.
Commissioning Sequence
Follow this verified sequence to bring the system online:
- Municipal inlet confirmation — verify water flow into the unit with stable pressure at or above 0.15 MPa.
- Pressure and parameter setting — confirm pre-charge pressure and HMI target pressure values match design intent.
- Point-start rotation check — briefly energize each pump to verify correct rotation direction. Reverse rotation indicates a phase swap and requires immediate correction.
- Constant pressure linkage test — run the system under steady demand and verify the VFD modulates frequency to hold the target pressure within the specified band.
- Peak-valley load simulation — simulate high-demand and low-demand scenarios to confirm pressure fluctuation stays within plus or minus 0.01 MPa. Record frequency, pressure, and current readings at each step.
- Data logging and handover — compile all readings into the commissioning report for client sign-off.
Technical Specifications
| Parameter | Value |
| Minimum inlet pressure | greater than or equal to 0.15 MPa |
| Target pressure range | 0.3 – 0.6 MPa (adjustable via HMI) |
| Pressure fluctuation (steady state) | less than or equal to plus or minus 0.01 MPa |
| Horizontal alignment tolerance | less than or equal to 2 mm/m |
| Ground resistance | less than or equal to 4 ohms |
| Max media temperature | less than or equal to 40 C |
| Max ambient temperature | less than or equal to 40 C |
| Maintenance clearance | greater than or equal to 600 mm all sides |
| Pressure vessel pre-charge | 70–80% of system working pressure |
Application Scenarios
Mid-Rise Residential Buildings
Residential towers in the 6–18 floor range typically require 0.3–0.5 MPa delivery pressure. The non-negative pressure design avoids creating a vacuum in the municipal supply pipe, which keeps the water utility compliant with local regulations while still boosting pressure to upper floors.
Commercial Office Complexes
Office buildings with variable occupancy patterns benefit from the VFD-driven pressure control. During early morning startup, the system ramps frequency to meet rising demand. During lunch hours and evening wind-down, the drive slows to conserve energy while maintaining stable pressure.
Hospital Water Supply
Medical facilities require uninterrupted water service. The CDWG unit multi-pump rotation logic ensures that no single pump bears continuous duty, and the pressure vessel provides short-term supply during pump switchover, preventing pressure dips that could affect clinical operations.
Frequently Asked Questions
What happens if municipal inlet pressure drops below 0.15 MPa?
The negative pressure eliminator valve opens automatically to prevent vacuum formation in the municipal pipe. The system will reduce output pressure proportionally or shut down depending on the control settings. This protects the public water network from being starved by the building demand.
How often should the pressure vessel pre-charge be checked?
We recommend checking pre-charge pressure every six months during routine maintenance. A gradual loss of pre-charge indicates bladder micro-leaks and the vessel should be replaced before it causes excessive pump cycling.
Can the unit operate without a pressure vessel?
Technically yes, but the pressure vessel plays a critical role in absorbing start-stop transients. Without it, the VFD will cycle more frequently, reducing pump and drive lifespan. The vessel is a standard component of the CDWG package for this reason.
Why is the grounding resistance specified at 4 ohms or less?
The VFD generates high-frequency switching noise during operation. Adequate grounding provides a low-impedance path for this noise to dissipate, protecting both the control electronics and personnel. Values above 4 ohms can allow stray voltages to build up on equipment enclosures.
What does the plus or minus 0.01 MPa pressure fluctuation specification mean in practice?
For a system set to 0.4 MPa, the actual pressure at the outlet will remain between 0.39 and 0.41 MPa under steady-state conditions. This tight tolerance ensures that fixtures on upper floors receive consistent flow regardless of demand fluctuations elsewhere in the building.
Why Choose Chaodun Pumps
Chaodun Pumps manufactures the CDWG non-negative pressure water supply unit in compliance with relevant domestic design and testing standards. Each unit undergoes factory pressure testing and commissioning verification before shipment. Our engineering team provides installation guidance and on-site commissioning support for projects requiring additional technical assistance.
For complete dimensional drawings, bypass connection diagrams, and commissioning record forms, please refer to the CDWG Non-Negative Pressure Variable Frequency Water Supply Equipment Installation and Maintenance Manual, available in English upon request.