duct bends losses

Duct bends losses are local pressure losses created when airflow changes direction through elbows, turns, and poorly aligned duct sections. In mining duct ventilation, bends are often added as headings advance or as equipment moves, and the cumulative impact can be large. Even if the fan’s nameplate looks strong, extra bend losses increase the required static pressure (Ps) and can shift the operating point, reducing end-of-duct airflow at the face.

Not all bends are equal. Losses rise when:

• Bends are sharp (tight radius), causing separation and turbulence.
• Multiple bends are close together, compounding disturbance and raising resistance.
• Transitions are misaligned, creating step changes and additional turbulence.
• Ducts are damaged or partially collapsed near bends, increasing blockage.

From a selection standpoint, bend losses must be included in the duct system pressure estimate. The correct approach is to define the required face airflow and then determine the realistic Q@Ps duty point after accounting for friction losses and local losses (including bends, reducers, and connectors). Selecting by free-air rating is risky because bend losses move the operating point into higher Ps where many fans deliver significantly less airflow.

Practical ways to reduce bend losses include improving duct routing, using smoother turns where possible, minimizing unnecessary elbows, and keeping fittings properly aligned and sealed. When the system must change frequently, a VFD can help maintain airflow as resistance increases, but it is still better to prevent avoidable losses than to “speed up” into noise and inefficiency.

Bottom line: bend losses are a common hidden cause of under-ventilation at headings. Treat duct routing as part of the ventilation design, and verify delivery at the duct end—not at the fan outlet.