A Pitot Tube is also popularly known as a Pitot Probe. It is a device used for flow measurement that measures the fluid flow velocity. It was invented by Henri Pitot in the early period of the 18th century who was a French engineer. It was modified by a French scientist named Henry Darcy in the mid-19th century. This modified version is the one that is currently used. A Pitot Tube is used to ascertain the airspeed of a water speedboat, an aircraft as well as in order to measure gas, air and liquid flow velocities in some industrial applications.
The Principle of Pitot Tubes
Pitot Tubes measure the air velocity or the flowing liquid. It can be considered as a differential pressure flow meter that measures two different types of pressures namely Total Impact Pressure and Static Pressure. The Total Impact Pressure is the addition of the Kinetic and Static pressures that are detected in the form of the impact of the flowing stream on the Pitot opening. In order to measure the Total Impact Measure, many Pitot Tubes use a tiny L-shaped tube with its opening directed towards the oncoming flow stream.
When you keep solid body stationery, and centrally in a pipeline that contains flowing liquid, the fluid’s velocity starts reducing because of the presence of the solid body. At the same time, you can also see the pressure of the fluid increase because of the Kinetic energy conversion into pressure energy. The velocity shows zero directly before the solid body. This particular point in the entire process is called the stagnation point.
You can measure the fluid flow by gauging the difference between the stagnation point or the stagnation pressure and the normal flow line pressure or the static pressure. The operating principle of a Pitot Tube is basically when the kinetic head converts into pressure head.
A pitot tube is essentially used in the experiments of wing tunnels and also on aircraft in order to measure the flow speed. This is the underlying purpose of a pitot tube. The tube is quite slender and contains two holes. You can find the front hole in the air stream which is meant for measuring the stagnation pressure or the stagnation point. The side hole is meant for measuring the static pressure. There are many types of Pitot tubes such as Type PA, Type PB, Type PC and much more.
Applications of Pitot Tubes
Pitot tubes have a lot of industrial applications. They are used in utility streams where you require high accuracy. They are also used in pipe systems and air ducts. Pitot tubes are also used in aircraft in order to measure the velocity of air flow.
Furthermore, you can also use a Pitot tube to map flow profile in a duct or a channel. Pitot tubes come with a multitude of advantages and disadvantages. The advantages of pitot tubes are:
- They are economical and easy to install.
- You can easily remove some types from the pipeline.
- Pitot tubes also do not consist of any moving parts. Therefore, it greatly minimizes frictional loss.
- They are extremely small in size, and hence, it can easily partake in the fluid flow without causing a shutdown of the flow.
- Pressure loss is also minimal with pitot tubes.
- You can easily install pitot tubes in extreme environments such as high-pressure conditions or high temperatures.
Despite the plethora of applications of pitot tubes, they also come with their fair share of limitations and disadvantages. They are as follows:
- The sensitivity can be disturbed by the flow direction.
- Pitot tubes are not suitable for sticky or dirty fluid such as sewage disposal.
- They have poor accuracy and low sensitivity. They also require a high-velocity flow.
- Pitot tubes have also been discovered to have restricted applications in various industries because they are prone to become clogged easily with foreign materials present in the liquid.
- Also, pitot tubes have no standardization.
- A change in the velocity profile of pitot tubes might also result in substantial errors. Due to a change in the velocity profile, it is also common to witness a super low differential pressure, and hence, it can be quite challenging to measure it.
That said, when pitot tubes are put against each other, their advantages outnumber the limitations significantly.
How to Select A Pitot Tube?
In order to select the perfect pitot tube for yourself, you need first to understand your requirement well. There are many distinct types of pitot tubes that are meant for different applications in the market. All of them have a unique purpose and function. Therefore, before deciding on the right pitot tube for your work, you must understand precisely what you need the pitot tube for in the first place. When it comes time to select a pitot tube for yourself, you must also check the features of the pitot tubes you have shortlisted as they all come with a distinct list of characteristics.
First of all, you need to pick up the right one for yourself among the six basic types:
1. Type PA
This one has fixed take-offs and has an attached mounting chuck. There is no reinforcement tubing added in this type of pitot tube.
2. Type PB
Type PB is similar to Type PA because it has fixed take-offs as well as an attached mounting chuck. However, there is a reinforcement tubing added in it, unlike the Type PA pitot tube.
3. Type PC
Type PC has removable take-offs but no reinforcement tubing or mounting chuck. That is why they are different from the other tube types.
4. Type PD
Type PC has removable take-offs but no reinforcement tubing or mounting chuck. That is why they are different from the other tube types.
5. Type PE
Type PC has removable take-offs but no reinforcement tubing or mounting chuck. That is why they are different from the other tube types.
6. Type PF
Type PC has removable take-offs but no reinforcement tubing or mounting chuck. That is why they are different from the other tube types.
Therefore, based on these diverse elements, you can choose the ideal one for your application.