Airflow is volume of air mass flow and static pressure is what drives it. Static pressure is of no significance other than to achieve the required airflow, But is so important to get right. It is the same concept between ampere and voltage, ampere being the running electricity, voltage is the differential that drives it. This is also the case for water volume flowing in a pipe and pressure head.

Combination of these 2 concepts gives you power consumption. This is true for airflow vs pressure, ampere vs voltage or water volume vs head.

Static pressure changes vs round pipe diameter.

At constant duct velocity, static pressure loss increases exponentially with decrease in duct diameter. In below example chart, using typical dust collector duct velocity of 20m/s, static pressure is seen to increase substantially when duct size approaches lower end of its diameter. It is this reason why vacuum cleaner uses vacuum pump that produces static pressure of 200mbar range, instead of blower. This knowledge alone has important implication on dust collector sizing and ductwork layout.

Static pressure and dynamic pressure

As air flow axially inside a duct, there is velocity as well as static pressure difference between 2 points of the duct that drives the airflow. The former is kinetic energy and the latter is potential energy. Both of these should be measured and calculated in blower fan testing. The sum of these 2 are total pressure.

Static pressure can be rather easily determined as in diagram below.

And a combination of Pitot tube and inclined manometer are used to measure velocity pressure, normally in term of mmWG. Airflow can be calculated from it by including air density (temperature) and duct diameter.