What Is a Pressure Sustaining Valve?
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A pressure sustaining valve is a hydraulically operated control valve designed to maintain a minimum upstream pressure in a water system. It automatically protects critical areas of a distribution network by ensuring pressure does not fall below a preset value, regardless of downstream demand.
In municipal water systems, industrial pipelines, fire protection networks, and irrigation systems, maintaining stable pressure is critical. A pressure sustaining valve plays a key role in preventing pressure collapse and protecting infrastructure.
What Does a Pressure Sustaining Valve Do?
In simple terms:
A pressure sustaining valve ensures that the pressure before the valve (upstream) does not drop below a set minimum. If upstream pressure begins to fall, the valve automatically throttles or closes to protect that pressure.
Why This Matters
Without a sustaining valve:
High downstream demand can starve critical areas
Pumps may cavitate due to low suction pressure
Fire protection systems may lose required pressure
Elevated zones may experience pressure collapse
How a Pressure Sustaining Valve Works
Most pressure sustaining valves are diaphragm-actuated hydraulic control valves that use line pressure and a pilot control system. They operate automatically, no external power required (unless it is an electrically assisted model).
Step-by-Step Operation
The pilot control senses upstream pressure
When upstream pressure is above the setpoint → the valve opens and allows flow
When upstream pressure drops to the preset minimum → the valve begins to close
If pressure drops further → the valve closes more to sustain the minimum pressure
The system continuously modulates to maintain the set pressure.
Common Applications of Pressure Sustaining Valves
Pressure sustaining valves are widely used in:
🔹 Pump Protection
Prevent low suction pressure that can damage pumps or cause cavitation.
🔹 Elevated Zones
Maintain pressure in high elevation areas where pressure can drop quickly.
🔹 Fire Protection Systems
Ensure required fire flow pressure is always available.
🔹 Municipal Distribution Systems
Maintain minimum system pressure across pressure zones.
🔹 Priority Flow Control
Prioritize one zone over another during high demand.
Real-World Example
Imagine a water main feeding two branches:
Branch 1 supplies a hospital
Branch 2 supplies irrigation
If irrigation demand spikes, it could reduce system pressure. Installing a pressure sustaining valve on the irrigation branch ensures that the hospital supply maintains its minimum required pressure. If pressure begins to drop, the valve restricts irrigation flow to protect the hospital line.
This is a common strategy in municipal and industrial water systems.
Pressure Sustaining vs. Pressure Reducing Valves
Although they sound similar, they perform opposite functions.
Valve Type | What It Controls |
Pressure Sustaining Valve | Maintains minimum upstream pressure |
Pressure Reducing Valve (PRV) | Limits maximum downstream pressure |
Key Difference:
A sustaining valve protects pressure before the valve.
A reducing valve protects pressure after the valve.
Both are essential, but they solve different hydraulic challenges.
Key Benefits of Pressure Sustaining Valves
✔ Protect critical infrastructure
✔ Prevent pressure collapse
✔ Improve system reliability
✔ Automatically adjust to demand changes
✔ No electricity required (standard models)
✔ Increase pump lifespan
Where Pressure Sustaining Valves Are Installed
Municipal water distribution systems
Industrial processing facilities
Irrigation networks
Fire protection systems
Booster pump stations
High-rise building supply systems
A pressure sustaining valve is a critical component in modern water distribution systems. By automatically maintaining minimum upstream pressure, it protects pumps, ensures fire flow availability, and prioritizes critical service zones.
If your system requires pressure stability, especially in multi-zone or high-demand environments, a pressure sustaining valve is often the right solution.
