Pitot tube

November 1, 2021

In the field of flow velocity measurement , there are many instruments that make it possible to assess such magnitude, but one of the most necessary to fulfill this task is undoubtedly the Pitot Tube.

An unknown name to many, this instrument is capable of measuring two pressures within a tube , and then finding an average between the two and determining a pressure and a relative velocity.

Given this dual character , the pitot tube has been consolidated in many industries and has quietly been involved in elements that we use on a daily basis.

In the next few lines, I will clarify this concept so that you can know in depth what this unique instrument is about and the benefits it has, to make the most of each of its capabilities.

What is a Pitot Tube?

The pitot tube is a set of tubes of various shapes, connected in different sectors of the tube to be measured, whose main function is to determine the flow rate or speed with which said fluid circulates in that tube.

In order to be able to measure this parameter, this tube uses two pressures within the tube, one generated when the fluid does not move and the other when it does, which translates the subtraction of both as differential pressure.

Why the pressure? Because in this case, the differential pressure is directly proportional to the speed , that is, as the pressure increases, the speed of the fluid increases.

In case you want to know the quantity precisely, you can simply use an equation, which quantitatively deduces this speed and the pressure.

What is a Pitot Tube for?

It is an instrument used in precision calculation, called in some terms, as total or stagnation pressure, which is nothing more than a sum between static and dynamic pressure.

In other words, this tube allows to measure the speed with which a certain flow circulates through a tube , which is important in any of the physical, industrial, mechanical jobs, among others.

This tube can also be used with other instruments to ensure the correct measurement in certain places, since both work synergistically and together, to achieve the proposed objective.

How does a Pitot Tube work?

The Pitot tube is an element that is inserted as an accessory in a hole in the tube, in order to maintain direct contact with the flow and thus be able to calculate through a shock, the speed with which it circulates inside the pipe.

At the time of being installed, you have to ensure that it is precisely in a straight section and away from any section where disturbances are generated, that is, the valves, connections or others.

It should be known that the pitot tube is in turn made up of two tubes, which using the same operating mechanism, one will measure the static pressure (without movement) and the other the dynamic pressure (with movement), which both will establish total or stagnation pressure.

Once inside, you will see how the height of the fluid will begin to grow, up to a certain point on the surface and once having the height, proceed to perform an equation, called the Bernoulli equation or in some models, it is shown by on a scale measuring with needles and even digital.

Bernoulli’s equation summarizes that the total pressure is the velocity squared, of how the flow circulates through the pipe. Simply put, pressures are directly proportional to flow velocity.

Pitot tube uses

The uses of the Pitot Tube are varied but have more relevance in places where elementary physics and engineering terms are applied . Some of the applications are intended as follows:

  • They are used in large diameter pipes , with generally clean fluids related to liquids and gases.
  • They are joined with manometers, to create an important piece in the aeronautical industry, called an aerometer. This element is capable of calculating the flow velocities, but in this case, of the air.
  • Determine the static pressure that the air has around the airplane when it flies.
  • It can be linked to speedometers , to determine how fast the car is traveling.
  • It is included in the tachometer , with an attached piece. Both work to determine the revolutions per minute with which the vehicle’s crankshaft is operating.

As you can see, the pitot tube is an indispensable element in the automobile, aircraft and vehicle industry in general, as a complement to other speed measuring instruments.

Pitot Tube Types

Pitot tubes do not present a wide variety, they are classified into two types. Well, it is an element that has been preserved since its appearance, since it is excellent at a functional level and because it is now being attached to other instruments to obtain other measurements. The types of pitot tube are:

  • Pitot tube type L or Pitot tube type Prandtl

This is a combined model, invented by Ludwig Prandtl, a physics-loving engineer. Here the Tube created by Pitot is joined with the ring of a manometer , in order to know the dynamic pressure that a fluid has in a given pipe.

  • Pitot Tube S or Stausscheibe Pitot Tube

The operating mechanism is the same as the previous one, except that it has a single orifice to be able to make measurements of the static, dynamic and total pressure of the fluids that circulate through a given pipe.

Both types are continuous, that is, one is born from the operating mechanism of the other. However, they have the same purposes, which is nothing more, than to make this important calculation of the flow.

Characteristics of a Pitot Tube

The Pitot Tube has a series of characteristics that will constitute its definition and functionality, since it shows in itself all the details about its design, structure and extra aspects that this instrument has. The main qualities are:

  • Its main function is to act as a flow meter.
  • Although it may not seem like it, in general terms they are very simple and cheap instruments .
  • Pitot tubes present variations in size , depending on each model.
  • It is one of the instruments that offers more precision , when it comes to measuring the speed of a fluid inside a tube.
  • It is easy to install, you just have to place it in a previously made hole on the back of the pipe.
  • As for the shape, it has a spherical part and then it bends, forming an L.
  • Its size is small.
  • The Pitot tube is an accessory that is located, against the current in which the flow circulates, to ensure that it collides with this instrument in order to make measurements.

Definitely, the Pitot Tube is a piece that has a wide number of qualities, which makes it an element with a lot of potential.

Importance of the Pitot Tube

The importance of this set of tubes lies in the fact that they are widely used in all sectors of daily life and that they have laid the foundations for the creation of new, more specialized flow measurement instruments.

In addition, it should be noted that the pitot tube not only determines the speed of the flow , but also the pressures, which is essential in different scenarios, for example, airplanes when they are flying, since there is a pressure that in itself collides with the airplanes, generated by air and the force of gravity.

Finally, the pitot tube is a preventive tool , because by marking the speed and pressure in a certain equipment or in an airplane or vehicle, it allows the person to lower the acceleration or act in a timely manner if there is a significant variation, which It allows to keep the whole element stable and avoid future accidents.

History of the Pitot Tube

The history of the Pitot Tube specifically begins in the 18th century, when an engineer and physicist, a native of the Parisian city, named Henri Pitot created this tube, in 1732.

It is born to be able to make measurements about the speed with which a flow or flow moves. To verify his invention, this remarkable scientist carried out the measurement in the Seine River.

However, the history of this instrument does not end there, as Henri Pitot established precedents for the specialization and evolution of this unique tube, to even measure different quantities than liquid flow, such as air.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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