Airflow Measurement Venturi (Differential Pressure)

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I measure the differential pressure of a 12-volt centrifugal blower fan using a 3:1 Venturi and a manometer filled with water. The red liquid is water with red food coloring added to it. Air flows from the fan across the end of the clear tube on the right side, and into a narrower section with one-third the cross-sectional area across the end of the tube on the left side. The venturi effect causes lower pressure in the narrower section. The difference between the height of water on the left side and the height of water on the right side is the differential pressure in height of water column. This pressure can be used with the diameters of the venturi to calculate air flow. I purchased the fan from an online retailer, specifically a 12-volt blower fan available at RobotShop.com. To better understand the process, watch this video: https://www.youtube.com/watch?v=v3APioRqdGg.