The static pressure curve of a fan is part of the fan performance chart that shows how static pressure varies with airflow at a given speed. It is one of the key tools engineers use to select and apply axial and centrifugal fans in industrial and mining ventilation systems.
Static pressure is the pressure associated with the potential energy of the air in the system, measured relative to ambient atmospheric pressure. It is the pressure that overcomes friction losses in ducts, filters, bends, diffusers and mine airways. In contrast, velocity pressure is associated with the kinetic energy of the moving air. The sum of static and velocity pressure at a point is called total pressure.
When a manufacturer tests a fan in a laboratory, they measure airflow and pressures at many operating points along the fan curve. For each airflow, they determine the static pressure the fan can develop. Plotting these values with airflow on the horizontal axis and static pressure on the vertical axis results in the static pressure curve. At low airflows, the fan can generate a relatively high static pressure. As airflow increases, static pressure generally rises to a peak and then falls off as the fan approaches its maximum capacity.
The static pressure curve is used together with the system resistance curve—which shows how much static pressure is required by the ductwork or mine airway at different flow rates. The point where the system curve intersects the fan static pressure curve is the operating point: here the fan’s static pressure capability exactly matches the system’s static pressure requirement, and the corresponding airflow is the actual flow you can expect.
Understanding the static pressure curve helps in several ways:
- It allows you to select a fan model and size that can provide the required airflow at the system static pressure.
- It shows how changes in system resistance (such as dirty filters or new duct branches) will shift the operating point.
- It helps identify unstable regions of operation, such as stall or surge, where static pressure may behave unpredictably.
In mining ventilation, knowledge of static pressure curves is especially important because long haulageways, regulators and raises create significant resistance, and high static pressures are common at main fans. Correctly matching fan curves to mine system curves ensures that legal air quantity requirements are met in all working areas.
In summary, the static pressure curve of a fan is the graph of static pressure versus airflow at a constant speed. It is an essential design and troubleshooting tool for anyone responsible for industrial or mining ventilation systems.
