CDWG Non-Negative Pressure Water Supply Unit — Hygienic Municipal Water Boosting Without Negative Pressure
In urban high-rise buildings and dense residential communities, maintaining stable water pressure without compromising the municipal supply network is a critical engineering challenge. Chaodun Pump’s CDWG Non-Negative Pressure Water Supply Unit solves this by directly utilizing the existing municipal pipe network pressure as a baseline, then boosting it through a variable-frequency pump system — without creating negative pressure that could affect neighboring users or draw contaminants into the supply.
Non-Negative Pressure Principle
The key to this system is its vacuum eliminator (negative pressure suppressor) that works in tandem with the pressure-boosting pump group. When municipal inlet pressure is sufficient (≥0.15 MPa), water flows directly through the unit to the building’s internal network. When demand increases and pressure begins to drop, the vacuum eliminator opens to admit atmospheric air, preventing negative pressure formation in the municipal pipe. Simultaneously, the variable-frequency pumps increase speed to maintain the target output pressure — typically set between 0.3 and 0.6 MPa depending on building height and fixture requirements.
This approach eliminates the need for intermediate storage tanks that can become contamination points, while ensuring that your building’s water demand does not steal pressure from the surrounding network. It is a genuinely hygienic and community-friendly solution.
Integrated Diaphragm Pressure Vessel
Alongside the pump group, a pre-charged diaphragm pressure vessel (preset at 70%-80% of the system working pressure) serves as a buffer that absorbs small demand fluctuations without triggering pump cycling. This significantly extends pump bearing and seal life, reduces energy consumption from unnecessary start-stop cycles, and keeps pressure stability within ±0.01 MPa even during peak-to-valley demand transitions.
Variable Frequency Drive and PID Control
The unit’s human-machine interface allows operators to set target pressure values and configure pump rotation logic. The VFD controller continuously monitors outlet pressure via a feedback transducer and adjusts pump speed in real time through a PID control loop. When demand is low, a single pump operates at reduced frequency. As demand increases, additional pumps stage in and each runs at the optimal speed point. This cascaded variable-frequency approach typically achieves 30%-50% energy savings compared to constant-speed pumping with throttling valves.
Compact Installation — No Anchor Bolts Required
The entire unit arrives as a skid-mounted assembly. It sits level on a reinforced floor surface, adjusted to a levelness tolerance of ≤2 mm/m using vibration isolators — no pre-embedded anchor bolts are needed. The inlet and outlet connections use flexible rubber joints to prevent pipe stress from transferring to the equipment body, and bypass piping requires independent support structures.
Electrical connections are straightforward: the control cabinet junction box faces outward for accessibility, signal and power cables are routed in separate conduits, and the grounding resistance is maintained at ≤4 Ω. The unit requires a minimum 600 mm clearance on all sides for routine maintenance access.
Technical Specifications
| Minimum Municipal Inlet Pressure | ≥0.15 MPa |
| Target Output Pressure Range | 0.3-0.6 MPa (adjustable via HMI) |
| Pressure Stability | ≤±0.01 MPa |
| Diaphragm Vessel Pre-charge | 70%-80% of working pressure |
| Maximum Medium Temperature | ≤40°C |
| Maximum Ambient Temperature | ≤40°C |
| Installation Levelness | ≤2 mm/m |
| Grounding Resistance | ≤4 Ω |
| Minimum Maintenance Clearance | 600 mm all sides |
Installation and Commissioning Procedure
Step 1: Pre-Installation Checks
Verify that the municipal inlet pressure meets the minimum 0.15 MPa requirement. Confirm flow rate and pressure parameters match your building design. Check that the medium temperature does not exceed 40°C and ambient conditions are within specification. Verify control cabinet power phase sequence and grounding continuity.
Step 2: Mechanical Positioning
Place the unit on a level, reinforced floor. Adjust using vibration isolators to achieve ≤2 mm/m levelness. Connect inlet and outlet piping with flexible rubber joints — do not allow pipe stress to bear on the equipment body.
Step 3: Electrical Connections
Route signal and power cables in separate conduits. Connect grounding with verified ≤4 Ω resistance. Set the diaphragm vessel pre-charge to 70%-80% of the intended working pressure.
Step 4: HMI Configuration
Through the touchscreen interface, set the target pressure (default range: 0.3-0.6 MPa) and configure the pump rotation sequence. Confirm the vacuum eliminator moves freely between open and closed positions.
Step 5: Commissioning
Open the municipal inlet valve. Jog each pump to verify correct rotation direction. Run a constant-pressure integration test with simulated load variations to confirm pressure fluctuation stays within ±0.01 MPa. Record operating frequency, pressure, and current data. Complete acceptance documentation.
Typical Applications
- High-rise residential buildings — Upper-floor water supply without tank contamination risk
- Urban residential communities — Centralized boosting from municipal mains to multiple buildings
- Office complexes — Stable pressure for HVAC makeup water and domestic supply
- Schools and hospitals — Hygienic water supply where storage tanks are undesirable
- Hotels — Consistent hot and cold water pressure across all floors
- Industrial facilities — Process water supply requiring stable pressure without negative impact on the municipal grid
Maintenance and Long-Term Reliability
The CDWG unit is designed for minimal routine maintenance. Key periodic checks include verifying the vacuum eliminator’s free movement quarterly, inspecting flexible rubber joints for degradation annually, testing the diaphragm vessel pre-charge pressure semi-annually, and reviewing VFD operating logs for unusual frequency or current patterns. The absence of a storage tank eliminates the need for tank cleaning and disinfection — a significant operational advantage over traditional rooftop tank systems.
Frequently Asked Questions
Q: What happens if municipal pressure drops below 0.15 MPa?
The vacuum eliminator opens fully to prevent negative pressure formation, and the control system adjusts pump operation to maintain output pressure within available inlet conditions. If the inlet pressure is insufficient for the required duty, the system will alert operators through the HMI.
Q: Can this unit replace an existing rooftop tank system?
In many cases, yes. The non-negative pressure unit eliminates the need for intermediate storage, reducing contamination risk, structural load, and maintenance requirements. However, a hydraulic analysis of your specific building is recommended to confirm suitability.
Q: How does the system handle power fluctuations?
The VFD controller includes built-in protection against overvoltage, undervoltage, and phase loss. The diaphragm vessel provides short-term pressure buffering during brief power interruptions, giving occupants time before pressure drops become noticeable.
Q: What is the expected energy saving compared to traditional constant-speed pumping?
Depending on the load profile, variable-frequency control typically achieves 30%-50% energy savings over constant-speed pumps with throttling or bypass valves. The savings come from matching pump speed to actual demand rather than running at full speed and wasting excess energy.
Need a Non-Negative Pressure Water Supply Solution?
Chaodun Pump engineers have designed CDWG Non-Negative Pressure Water Supply Units for residential, commercial, and municipal projects across diverse building types. We provide site-specific hydraulic analysis, equipment sizing, and commissioning support. Contact us to discuss your project’s water supply requirements.