What happens to pressures when air travels through a restriction?

When air travels through a restriction, such as a narrowing in a duct or an orifice, the behavior of static and velocity pressures is governed by the principles of fluid dynamics, specifically Bernoulli's principle. As air enters a restricted area, its velocity increases due to the conservation of mass. Since the area available for flow decreases, the air must speed up to maintain mass flow continuity.

As the velocity of the air increases, the static pressure decreases. This is because energy must be conserved; as kinetic energy (associated with velocity) increases, potential energy (which can be related to static pressure) decreases. Therefore, within a restricted flow, we observe that the static pressure drops while the velocity pressure rises, highlighting the inverse relationship between these two forms of pressure.

This understanding is vital in various applications such as HVAC, where managing air pressure and flow is crucial for system efficiency and performance. Additionally, recognizing how pressure changes in response to restrictions can help in troubleshooting and designing systems for optimal airflow and pressure characteristics.