What Is a Non-Negative Pressure Water Supply Unit?
A non-negative pressure water supply unit (also called a non-negative pressure variable-frequency water supply system, direct-connection water booster unit, or stack-pressure water supply equipment) is an intelligent, energy-saving water pressurization solution that connects directly to municipal water mains without creating negative pressure. By utilizing the existing municipal water pressure as a baseline and adding variable-frequency pump boosting on top, it delivers stable, high-pressure water to high-rise buildings, commercial complexes, and industrial facilities while fully complying with municipal water network protection regulations.
Installation Guide — Step by Step
Pre-Installation Checks
Before unpacking and positioning the non-negative pressure water supply equipment, verify the following prerequisites:
- Municipal inlet pressure: Must be ≥ 0.15 MPa to ensure proper stack-pressure () effect. Measure at the point of connection using a calibrated gauge.
- Maintenance clearance: Reserve at least 600 mm of clearance on all four sides for future servicing and component replacement.
- Parameter verification: Confirm rated flow rate and pressure match your system design. Medium temperature must not exceed 40°C; ambient temperature must not exceed 40°C.
- Electrical check: Verify control cabinet power phase sequence and grounding connection before energizing.
Installation Procedures
- Positioning & Leveling: Place the direct-connection water booster system on a level, solid foundation. Use vibration isolators to adjust to a horizontal tolerance of ≤ 2 mm/m. No pre-embedded anchor bolts are required—the equipment’s weight and anti-vibration mounts provide sufficient stability.
- Pipe Connections: Connect inlet and outlet pipes using flexible rubber joints. Never allow pipeline stress to transfer to the equipment body. Bypass piping must have independent supports to prevent mechanical load on the unit.
- Electrical Wiring: Route the control cabinet junction box facing outward for accessibility. Separate signal cables and power cables into different conduits, securely fastened along the raceway. Grounding resistance must be ≤ 4Ω.
- Pressure Vessel Pre-Charge: Set the (pressure tank) pre-charge pressure to 70%–80% of the system operating pressure. Verify with a calibrated pressure gauge before closing the valve.
- HMI Configuration: Through the human-machine interface, set the target pressure (default: 0.3–0.6 MPa) and pump rotation-start logic. Confirm that the negative-pressure eliminator is in the free open/close position. Open the municipal inlet valve before starting.
Commissioning Process
Follow this sequence for safe and thorough commissioning of your non-negative pressure variable-frequency water supply unit:
- Municipal inlet confirmation: Verify water supply is stable at the required inlet pressure.
- Pressure & parameter setting: Input target pressure, pump rotation schedule, and alarm thresholds into the PLC/HMI.
- Jog test (): Momentarily start each pump to verify correct rotation direction and absence of abnormal vibration or noise.
- Constant-pressure test: Start the system in automatic mode and verify that all pumps maintain the set pressure under steady load.
- Peak/valley load simulation: Simulate maximum and minimum demand conditions. Pressure fluctuation must not exceed ± 0.01 MPa.
- Data recording: Log frequency, pressure, and current readings for each pump at minimum, nominal, and peak operating points.
- Acceptance sign-off: Complete the commissioning report and obtain authorized signatures.
For complete dimension drawings, bypass connection diagrams, and commissioning record forms, refer to the “CDWG Non-Negative Pressure Variable-Frequency Water Supply Equipment Installation & Maintenance Manual” (PDF / English version available upon request).
Technical Specifications
| Parameter | Specification |
|---|---|
| Municipal Inlet Pressure (Min.) | ≥ 0.15 MPa |
| Target Pressure Range | 0.3 – 0.6 MPa (adjustable) |
| Pressure Fluctuation (Steady State) | ≤ ± 0.01 MPa |
| Medium Temperature (Max.) | ≤ 40°C |
| Ambient Temperature (Max.) | ≤ 40°C |
| Grounding Resistance | ≤ 4Ω |
| Leveling Tolerance | ≤ 2 mm/m |
| Maintenance Clearance | ≥ 600 mm (all sides) |
| Control Mode | Variable-frequency (VFD) + PLC auto-rotation |
| Pressure Vessel Pre-Charge | 70% – 80% of system operating pressure |
Why Choose a Non-Negative Pressure System?
Unlike traditional water booster systems that require intermediate water tanks (which introduce contamination risk and occupy significant space), a non-negative pressure water supply unit connects directly to the municipal main. The key advantages include:
- Energy savings: Utilizes existing municipal pressure as a baseline, so the VFD pumps only add the differential pressure needed — often 30%–50% less energy than conventional booster systems.
- Water quality protection: Fully sealed design eliminates open-tank contamination, ensuring drinking-water-grade hygiene throughout the distribution network.
- Municipal compliance: The negative-pressure eliminator prevents any back-suction from the municipal network, meeting local water authority regulations.
- Compact footprint: No intermediate tank room needed — the entire skid-mounted unit fits in a standard mechanical room.
- Intelligent control: PLC-based auto-rotation ensures even wear across all pumps, extending service life and reducing unplanned downtime.
Frequently Asked Questions
Q1: What is the minimum municipal inlet pressure required?
The non-negative pressure water supply equipment requires a minimum municipal inlet pressure of 0.15 MPa. This ensures the stack-pressure () effect functions correctly. If your site has lower inlet pressure, consider our booster pump station variant instead.
Q2: Does the unit require anchor bolts or a special foundation?
No. The equipment is designed for direct placement on a level, solid floor. Vibration isolators provide leveling (tolerance ≤ 2 mm/m) and shock absorption. This significantly reduces civil engineering costs and installation time.
Q3: How stable is the output pressure?
Under normal operating conditions, the variable-frequency control system maintains pressure fluctuation within ± 0.01 MPa. During peak-to-valley load transitions, the PLC automatically adjusts pump speed and rotation to maintain constant pressure without water hammer or pressure spikes.
Q4: Can this system be used for hot water applications?
The standard model is rated for medium temperatures up to 40°C. For hot water applications (e.g., HVAC systems, industrial process water), we offer a high-temperature variant with specially rated seals and gaskets. Contact our engineering team for details.
Q5: What maintenance is required?
The non-negative pressure variable-frequency water supply system is designed for low-maintenance operation. Recommended checks include: quarterly inspection of vibration isolator condition, semi-annual verification of pressure vessel pre-charge, annual calibration of pressure transducers, and periodic review of pump bearing vibration and temperature trends.
Q6: How does the negative-pressure eliminator work?
The negative-pressure eliminator () is a vacuum-breaking valve that automatically opens if the suction pressure drops below a safe threshold, preventing any backflow or vacuum formation in the municipal main. It remains in a free open/close state during normal operation and requires no manual intervention.
Why Choose Chaodun Pump?
As a leading manufacturer of industrial and commercial water supply solutions, Chaodun Pump delivers non-negative pressure water supply units that meet international standards for performance, energy efficiency, and municipal compliance. Every unit undergoes rigorous factory testing — including hydrostatic pressure tests, variable-frequency response verification, and full-load commissioning — before shipment. Our technical support team provides on-site installation guidance, commissioning assistance, and after-sales service worldwide.
Contact us today for a free consultation on selecting the right non-negative pressure water supply unit for your project.