The Pilot Tube

A pilot tube is used to measure the flow speed of a gas. A gas flows with density and velocity parallel to some small openings, which we name point 1. The Pressure in the left arm of the manometer (the thin pipe), which is connected to these openings, is the Static pressure in the gas Stream.

At point 2, the velocity is reduced to 0 as the gas stagnates.

Applying Bernoulli’s Equation to points 1 and 2, we get:

The manometer reads for the difference in pressure, so we can substitute and solve for , giving us: