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To ensure a uniform air flow the fan should be preceded by a straight duct section with a cross-section area equal to half of that of the fan. The length of the duct section should be 3 ÷ 4 D (D is the inner diameter of the fan). The length of the straight duct section downstream of the fan should be 1.5 ÷ 2 D. Reduction of the recommended duct length values results in a drop of the fan pressure and performance. To reduce noise and vibration use the VVGF flexible joints.
Axial fans without upstream ducting must be equipped with the VK-VO inlet cone to improve the air flow parameters.
If the axial fan is a terminal device of the ventilation system (i.e. there is no downstream ducting) the unit must be equipped with a diffuser to reduce the air flow velocity and the fan dynamic pressure. Reduction of the air discharge velocity results in a significant reduction of shock losses which are proportional to the square of velocity decrement.
The fan should not be equipped with a downstream contractor.
To install the fan directly downstream of a bend (elbow) use a curved section with a large bending radius or an array of internal guide vanes.
When changing from a smaller diameter to a larger one use a connector diffuser with the maximum opening angle of 12°.
To ensure normal operation of the fan in an obstructed space make sure to provide for a sufficient distance between the inlet and outlet flanges and the floor, walls, bulky equipment and obstacles.
