To measure static pressure, use a manometer with at least two pressure ports to check both the suction and discharge pressure of the duct, and add these figures together. Static pressure is usually measured in inches of water column, which is defined as the pressure exerted by one inch of water at the temperature of its maximum density.
To test a duct’s static pressure, first choose the locations for your test holes, then drill the holes, take positive and negative readings in the supply, and return plenums with a manometer. The sum of these readings is the static pressure. This measurement can be compared with manufacturer specifications to ascertain whether the duct system is performing at its rated capacity.
Static pressure is also used in aircraft to measure altitude and airspeed. As atmospheric pressure is uniform at particular altitudes, constant measurements of this pressure are taken by a small cavity on the airplane’s exterior called the static port. These measurements are interpreted by the airplane’s static pressure system and pitot pressure system to give an approximate altitude and airspeed. Depending on the weight, airspeed and position of the static port, these measurements can become inaccurate, so it is important to identify the most optimal position for the static port during the design of the aircraft to ensure consistency between atmospheric pressure and the static pressure system.