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Another method to create a pressure drop in a fluid system is to use an existing elbow in the piping system. It has been determined that the pressure of fluid will show a slight pressure differential as it passes through an elbow. The fluid that flows near the inside radius of the elbow will have a slightly lower pressure than the fluid that flows on the outer radius of the elbow. The figure below shows an example of this type of meter. One can also notice that the distance the fluid travels on the outer radius of the elbow will be longer than the distance on the inner radius of the elbow. Two low-pressure ports are provided on the inner side of the elbow to provide the lower-pressure reading, and two ports are provided on the outer side of the elbow to provide the higher-pressure reading so that a better average of each pressure is determined. The amount of pressure difference from this type of sensor is very small and a manometer or ultralow differential pressure sensor must be used to sense it. The pressure difference is used in a calculation to determine fluid flow. The amount of pressure difference will increase when the fluid flow increases, and the pressure difference will decrease when the fluid flow decreases.
ABOVE: Pressure ports are located on the inside radius and outside radius
of an elbow to measure the small amount of pressure drop that occurs
when fluid flows through the elbow.
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