**Velocity at a Point using a Pitot Tube**

A combination of piezometer and pitot tube can be used to obtain the velocity at a specific point. Static pressure can be measured using a piezometer. The Pitot tube, as shown in the figure, can be used to measure the stagnation pressure. Stagnation pressure is the pressure when the flow has a stagnation velocity (i.e., V = 0). By perfectly aligning the Pitot tube with the flow, the flow will come to a stop at the tip of the Pitot tube, hence providing the stagnation pressure measurement.

Applying Bernoulli's equation between points 1 and 2 as shown in the figure, and canceling the elevations (equal values) gives,

Since V_{2} = 0, the velocity at point 1 is

where p_{1} and p_{2} are known from the height of the fluid column in the piezometer and Pitot tube, respectively.

**Energy and Hydraulic Grade Lines**

The energy grade line (EGL) and the hydraulic grade line (HGL) provide a graphical interpretation of Bernoulli's equation. The EGL represents the total head available with respect to a chosen datum (i.e., a reference line, as shown in the figure).

Sometimes, this is also referred as the piezometric head and is the height a fluid column would rise in a piezometer. For example, the EGL and HGL for frictionless flow in a duct are shown in the figure.

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