A duct elbow changes the direction of airflow while consuming installation space and adding resistance. Angle, radius, section shape and connection details all affect the result. A drawing that specifies only “90-degree elbow” leaves several important purchasing decisions unresolved.
Reserve the turning envelope
For round ductwork, state nominal diameter, angle and the required centreline or throat-radius basis. For rectangular ductwork, identify width and height in the installed orientation, turning plane and the chosen construction. Include flanges, insulation and assembly clearance in the overall envelope.
Lindab's segmented bend data separates angle, nominal connection size, radius and installation dimensions. These are not interchangeable measurements. A compact elbow may fit the space while requiring a different pressure-loss allowance from a larger-radius fitting.
Check the neighbouring fittings
The airflow entering an elbow may already be uneven after a fan, transition or branch. Closely spaced bends can create a different operating condition from an isolated fitting. Show the surrounding route to the designer rather than comparing elbows outside their installation context.
Turning vanes may be part of a rectangular-elbow design, but should be selected and supported for the intended duty. They also affect cleaning access and can be inappropriate for some contaminated air streams. There is no universal vane arrangement that can be copied into every ventilation or extraction system.
Confirm the joint and conveyed air
Match spigot, flange or clamp connections to the adjoining system. Specify material, temperature, pressure and sealing requirements, including any cleaning or corrosion exposure. A metal fitting's appearance does not establish fire performance or suitability for hazardous exhaust.
Plan support so the elbow does not impose unintended loads on equipment connections. Where deposits can accumulate, provide an appropriate inspection and cleaning arrangement. Resolve these features before installation space is occupied by other services.
Compare round and general duct elbows with rectangular elbows. Send shengtongjh a dimensioned route sketch with airflow and connection details to coordinate the fitting.