On a fan, the word “intake” refers to the side where air enters the fan before it passes through the impeller and is discharged. Manufacturers often label one end of the housing as “intake” and the opposite end as “discharge” or “outlet”, sometimes using arrows to show the direction of airflow. These markings are important so that installers connect the fan correctly into the ventilation system.
For an axial fan, air flows parallel to the shaft. The intake side is the open end where air is drawn towards the blades, and the discharge side is where air leaves the fan after being accelerated by the impeller. In many industrial and mining axial fans, the intake side may have a bellmouth or inlet cone to smooth the airflow, while the discharge side connects to a duct, plenum or free outlet. Labeling the intake helps ensure that the bellmouth faces the incoming air and that duct transitions are arranged correctly.
For a centrifugal fan, air enters the intake at the eye (centre) of the impeller and is then thrown radially outward into the scroll casing. The intake is usually a circular opening on the side of the housing, often fitted with a flanged inlet or inlet box. The discharge is located tangentially on the casing where the air leaves under pressure. Knowing which opening is the intake is essential when connecting ducts, filters and dampers, as these must be placed on the suction side if they are to operate and be maintained correctly.
On smaller equipment fans, especially electronic cooling fans and EC fans, the term “intake” may be printed on the frame together with small arrows showing rotation direction and airflow direction. The intake arrow shows which direction air enters the fan, while the airflow arrow points from intake to discharge. These markings prevent accidental reversal when mounting fans in panels, cabinets or heat exchangers.
In ventilation design, the word “intake” is also used more broadly to describe air that is entering a system. For example, intake air shafts, intake drifts and intake ducts all refer to parts of the system that carry fresh air towards the mine or building. When a drawing labels a fan as being on the “intake” side of the system, it means the fan is connected to air that is still relatively clean and fresh, rather than exhaust air from contaminated zones.
In summary, “intake” on a fan simply marks the side where air enters. It helps installers correctly orient the fan and connect it to the right ductwork, ensuring that the designed airflow pattern and performance are achieved in industrial and mining ventilation systems.
