Low-Flow Instability in PRVs: Bypass the Problem or Solve It?

Water distribution systems demand efficiency, reliability, and stability, especially under low-flow conditions. Yet, many pressure reducing valves (PRVs) struggle when demand drops below 10%-20% of their nominal capacity.

Research has shown a strong correlation between unstable PRV operation and higher occurrences of pipe rupture and water loss. Fluttering and pressure fluctuations also accelerate wear on pipelines. The result? System inefficiencies, leaks, and damage to infrastructure that require costly maintenance.

To solve the problem, most industry solutions introduce workarounds, like V-port trims and external bypasses, which come with significant limitations.

There are two common methods that most manufacturers rely on to combat low-flow instability: V-port trims and external bypasses. But these approaches have inherent limitations and shortcomings:

V-port:

1. Limited effectiveness below 10% flow – V-ports help stabilize pressure down to 10% of the nominal flow. Below that, a bypass is still required.
2. Restricted flow capacity – The smaller passage area in a V-port reduces the valve’s Kv (flow coefficient). If designers overlook this, they may miscalculate system.

External bypass:

1. Increased complexity & maintenance – A bypass adds extra components to the system, increasing installation and operational costs, and requiring more frequent servicing.
2. Larger space requirements – Extra piping and devices increase the system’s footprint, making installations cumbersome.
3. Higher setpoint at low flow – Since the bypass valve’s setpoint is always higher than the main PRV, nighttime or low-flow conditions result in increased pressure, leading to more leaks and higher water losses.
4. Reliance on direct-acting PRVs – Many bypass solutions depend on direct-acting pressure reducing valves, which are unreliable. Their setpoints can shift with flow, sometimes deviating by up to 2.5 bar.

Ultimately, these workarounds may help mitigate instability, but they don’t address the root cause—the inability of standard PRVs to handle ultra-low flow rates effectively.

The DOROT S300 series eliminates the need for external bypasses and v-ports, by seamlessly regulating flow down to 1 m³/h at any valve size.

No instability, no fluttering, just consistent, reliable pressure control.

Key Advantages of the DOROT S300:

• Full-Range Stability – The S300 maintains precise pressure regulation, from high to ultra-low flow, without extra components.
• No External Bypass Needed – A simplified system means reduced complexity and lower installation costs.
• Superior Durability – By eliminating fluttering, the valve ensures a longer system lifespan, with minimal maintenance.
• Compact & Efficient – Without a bypass, installations take up less space—perfect for tight or retrofit applications.
• Consistent Setpoint – Unlike direct-acting PRVs, the S300 holds a steady pressure setpoint across all flow conditions, ensuring accurate and reliable control.

For years, bypasses and V-ports have been the default industry response to low-flow instability. But why accept a workaround when a true solution exists?

The DOROT S300 redefines PRV performance by delivering reliable, full-range pressure regulation, without the inefficiencies of traditional designs.

When it comes to PRVs, the choice is clear: Don’t bypass the problem. Just solve it.

Heimann, A. The Economic And Operational Implications Of Utilizing A Low-Flow Bypass Pressure Reducing Valve: An In-Depth Analysis, 2024