Flow Measurement

# What is a pitot tube and what is it used for

#### What is a pitot tube and what is it used for

A pitot tube is used to measure pressure and it is used in pipelines to measure the fluid flow. This device is widely used to measure the airspeed of an aircraft and it is also used for many industrial applications to measure the velocities of liquid air and gas. The pitot tube measures the local velocity at a given point in a flowing stream and not the average velocity in the pipe. Pitot tubes are called line inserted devices because they can be installed in, flow stream. The pitot tube probe has two parts and it can sense the static and dynamic pressure in the fluids. Pilot tube is the cheapest way to measure the fluid flow

#### How does a pitot tube work

A pilot tube can be considered as a small cylinder which is placed in a way that fluid can enter so it would be opposite to the fluid flow it’s one end is open and the other end is closed because of this the fluid that enters won’t be able to flow further and it will come to a static position. The diaphragm inside the pilot tube will separate the static fluid pressure from the total system pressure. The difference between these two measurements is the fluid flow rate. A pilot static tube is a flow velocity meter and it is capable to measure fluid velocities as a localized point. The energy conversion takes place at the stagnation point. Potential energy is converted into kinetic energy. A pressure higher than the dynamic pressure results from the kinetic to potential conversion. Static pressure is compared to the dynamic pressure-flow so that it can be measured with the help of a differential manometer.

#### How pitot tubes are constructed

A pitot tube is a slender tube that has two holes and it is used to calculate the velocity of the fluid that flows through the pipe. A pilot tube is a small round cylinder with one end opened like a small hole and the other end closed. A separate chamber can be seen in the pilot tube and that would be filled with fluid and it has static pressure. The chambers are separated by diaphragm, so if the pilot tube is installed in the flow stream, then it would measure the direct pressure at the contact pilot tube hole, and the second measurement is needed for the static pressure and the difference between these two measurements would be dynamic pressure. To measure the static flow the pressure sensing element must be arranged properly. The axis of the tube measuring the static pressure should be perpendicular to the boundary

#### How do you install a pitot tube

The pitot tube must be installed perpendicular to the duct. The head must be kept parallel facing the flow. If it is required to measure the speed of the fluid then the instrument must be placed in the opposite direction of the fluid.

#### What are the advantages of a pitot tube

• It is easy to install
• This device can be removed from a process without shutting down the process
• Design and construction is simple
• Produce energy saving compared to the equivalent orifice
• It can be used to measure flow in large water pipes and air gas ducts
• It doesn’t have any moving part
• It is small in size and can be used in tight space
• Long life
• Pressure loss is low
• Low cost

#### What are the disadvantages of the pitot tube

• Clogging could happen if there is foreign material in the liquid
• It must not be used in places where accuracy is important
• It won’t work properly in dirty streams
• Low rangeability
• Low sensitivity
• It would only work properly in high-velocity flow

#### What are the applications of the pitot tube

• It is used in aircraft to measure the speed
• It can measure the wind speed in a tunnel
• It can measure the speed of air or gas when the pipe is closed
• It is used in hostile environments
• HVAC commissioning
• It is used in marine and aeronautical speedometers