duct leakage

Duct leakage is one of the biggest hidden reasons auxiliary ventilation underperforms underground. Even when the fan is correctly sized, leaks at joints, couplings, damaged sections, or poorly fitted connections can divert airflow before it reaches the working face. The result is familiar: the fan sounds strong, but the face feels under-ventilated.

Leakage matters because the duct system is designed to deliver a specific end-of-duct airflow. If airflow escapes along the route, the fan must either produce more total airflow (often not possible at the required static pressure) or the face airflow drops. Leakage effectively shifts the system behavior and can move the operating point away from the intended Q@Ps duty point.

Common leakage causes include:

• Poor joint sealing at couplers and duct connections.
• Damage from abrasion, impacts, or repeated relocation.
• Incompatible components leading to loose fits or difficult alignment.
• Maintenance gaps where small tears become major leakage over time.

Reducing leakage is often the most cost-effective way to improve ventilation performance. Practical steps include using higher-quality ducting where required, standardizing connectors, inspecting joints routinely, replacing damaged sections promptly, and minimizing unnecessary bends that stress connections. Good leakage control can increase end-of-duct airflow without changing the fan, because it effectively reduces wasted flow and lowers the “effective” system demand.

Leakage also influences the choice between forcing and exhausting duct ventilation. For exhausting configurations, leakage can reduce capture effectiveness because leaks may draw in surrounding air rather than extracting contaminants at the face. Regardless of configuration, the selection should always be verified against the performance curve at the intended duty point and realistic leakage assumptions.

Bottom line: treat duct leakage as a primary design and maintenance variable. In many mines, improving duct integrity delivers a larger practical gain than simply buying a bigger fan.