The pitot tube traverse is the most accurate and reliable method for measuring airflow through a duct. Traverse readings should be taken on all fans, supply, and exhaust. When finding a location for your traverse make sure the duct is straight and about 6 to 10 duct diameters downstream from any elbows, transitions, or branches. The pitot tube tip should always be pointing into the airstream. The pitot tube traverse is also a good way to compare two different methods of airflow measurement. A good example is reading a sidewall diffuser with your flow hood and comparing that reading with a duct traverse taken upstream. If the readings do not match then a "Correction Factor" may be needed. Now lets talk about how a pitot tube traverse works. There are three pressures that exist in a duct that has air flowing through it. It can be measured by using the formula Total Pressure (TP) = Static Pressure (SP) + Velocity Pressure (VP):

• Total Pressure (TP) - potential or explosive energy.
• Static Pressure (SP) - pressure that is exerted in all directions of a duct. When static pressure is equal to total pressure, there is no air flow.
• Velocity Pressure (VP) - the difference between total pressure and static pressure.