1. Introduction to fans

Fans control the flow of air. There are a number of ways of controlling airflow.

The diagram illustrates all three methods.

1. Guide vanes.

2. Adjustable pitch blades.

3. Throttling valve.

Vanes, pitch blade and throttle valve
methods of air flow control in fans.

2. Fan performance

The performance of a fan can be graphed as seen in the
fan curve and system curve below.

The performance, not surprisingly, has similarities to that of pump performance.

As the airflow increases, the pressure dips, this is seen in the fan curve.

The air is fed into an arrangement of pipes and other devices that form a system.

The operating point for the fan is at the intersection of the two curves.

You should note that the frictional effect of the system soaks up some power.