A pitot tube is an instrument for measuring a flowing fluid’s velocity (speed). Pitot tubes are used in anemometers to calculate airspeed in wind tunnels and aircraft in flight. They also measure the flow of liquids. Let us learn more about pitot tube and their operation in this article.
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What is a Pitot Tube?
A pitot tube or a pitot probe is a flow measurement appliance used to calculate the fluid flow velocity. French engineer Henri Pitot invented the pitot tube in the early 18th century. In the mid-19th century, French scientist Henry Darcy altered it to its modern form.
Pitot tubes are widely utilised to determine a boat’s water speed, the airspeed of an aircraft, and measure air, liquid and gas flow velocities in various industrial applications.
Pitot Tube Construction and Working
A pitot tube consists of two hollow tubes that measure pressure at various places within the pipe. One tube gauges the impact or stagnation pressure, and the other tube measures only the static pressure, usually at the pipe wall. These hollow tubes can be mounted separately in a pipe or installed together in one casing as a single device.
Pitot Tube Diagram
Pitot Tube Working Principle
The pitot meter comprises a tube that is directed towards the flow. The fluid penetrates through the impact hole, and apart from this, there can be two more holes in the pitot tube that act as static pressure sources.
Another pressure sensing component should be installed on the meter to measure the static pressure. The tube axis measuring the static pressure should be free from burrs so that the boundary is smooth, and it should be perpendicular to the boundary.
​​The pitot-static tube that has the static pressure inlet is shown below.
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A pitot tube is a cylinder with one end open and the other end closed. The fluid streaming through the pipeline enters the pitot tube and rests there. Another section within the pitot tube is filled with fluid with static pressure. A diaphragm separates both chambers.
The measure of dynamic pressure is given by the difference in level between the liquid in the tube and the free surface. Measuring the impact and static pressure connected to the proper differential pressure meter determines the flow velocity and thus the flow rate.
The flow rate is computed from the square root of the pressure. In estimating the flow rate from the pressure, the calculation is dependent on factors such as the location of the static tap and the tube design. The Pitot-static probe includes the static holes in the tube system to eradicate this parameter.
Pitot Tube Advantages
- Pitot Tube is portable and does not contain any moving parts.
- It is economical.
- Permanent pressure loss is low.
- Pitot tube can be easily installed on an existing system.
Pitot Tube Disadvantages:
- Foreign materials in a fluid can easily obstruct the pitot tube and disrupt normal reading.
- Less accurate
- Low range
Pitot Tube Application
- The pitot tube is used in utility streams.
- It is used in the air duct and pipe system.
- It is used in aircraft to measure airflow velocity.
- They are used for mapping flow profiles in a channel or duct.
Frequently Asked Questions – FAQs
How does the Pitot tube work?
The front hole estimates the stagnation pressure, while the side openings measure static pressure. The difference between these two measurements is called dynamic pressure – this is what is used to estimate airspeed.
Where is the pitot tube used?
Pitot tubes measure airspeed aboard aircraft in flight and the wind tunnel; they also measure the flow of liquids.
When was the pitot tube invented?
Henri Pitot, a French engineer, invented the pitot tube in the early 18th century. It was modified to its modern form in the mid-19th century by French scientist Henry Darcy.
Can the pitot tube measure static pressure?
A Pitot tube gauges total and static pressure from which air velocity can be calculated. The Pitot tube is inserted into the duct with the tip pointed toward the airflow.
How to measure pressure using a pitot tube?
Dynamic pressure is given by the differential pressure calculated between both pressures. The measure of dynamic pressure is given by the difference in level between the liquid in the tube and the free surface.
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