duct pressure loss

Duct pressure loss (pressure drop) is the static pressure required to push a target airflow through a ventilation duct system. In underground mining, duct pressure loss is often the difference between “the fan is running” and “the face is actually ventilated.” As headings advance, duct runs get longer and more complex, and the required static pressure (Ps) rises. If the fan cannot provide that Ps at the required airflow (Q), the operating point shifts and end-of-duct airflow can drop sharply.

Duct pressure loss is driven by a few practical factors:

• Length and diameter: longer ducts increase friction loss; smaller diameter increases velocity and raises loss significantly.
• Surface condition: rough or damaged duct surfaces increase resistance compared with smooth, well-maintained ducting.
• Fittings: reducers, connectors, and transitions add local losses.
• System layout: poor routing, sharp turns, and frequent relocations often increase losses over time.

For correct fan selection, do not rely on free-air airflow ratings. Underground duct systems rarely operate near 0 Pa. Instead, define the required airflow at the target location (often the duct end) and estimate the total duct pressure loss under expected conditions. This gives a realistic Q@Ps duty point for sizing.

In operations, reducing duct pressure loss can be as effective as upgrading the fan. Increasing duct diameter (where feasible), improving routing, reducing sharp transitions, and using better-quality ducting can lower resistance and increase delivered airflow. A VFD can help maintain delivery as duct losses grow, but it should not be used to compensate for avoidable system inefficiency. The best results come from treating duct pressure loss as a controllable design and maintenance variable—measured, managed, and reflected in the duty point.