Principle of operation: A pitot tube flowmeter for wet compressed air operates on the differential pressure principle. It consists of two ports: a stagnation (or impact) port facing upstream and a static port facing sideways. As the wet compressed air flows through the pipe, the stagnation port faces directly into the flow, causing the air to decelerate momentarily and creating a high pressure point. The static port measures the static pressure of the flowing air.

Differential pressure measurement: The pressure difference between the stagnation pressure and the static pressure is measured by a pressure sensor. This pressure difference, known as the dynamic pressure, is directly proportional to the velocity of the air flow according to Bernoulli’s principle.

Calculating the flow rate: By measuring the differential pressure, the pitot tube flow meter calculates the velocity of the wet compressed air. In addition, the meter typically includes temperature measurement capabilities. Using the temperature data, the meter can calculate the volume flow of the air and compare it to reference conditions, ensuring accurate measurement regardless of changes in temperature and pressure.

Advantages of Pitot tube flow meters:

  • Simple design: Pitot tube flow meters have a simple design, consisting of only a tube and a pressure sensor. This simplicity makes them easy to install and maintain.
  • Suitable for wet air: Pitot tube flowmeters are suitable for measuring wet compressed air because they do not rely on heat transfer and are less sensitive to moisture content than thermal mass flowmeters.
  • Wide range of applications: They can be used in a wide range of industrial applications, including HVAC systems, pneumatic conveying and compressed air systems.
  • Low pressure drop: Pitot tube flowmeters typically have a low pressure drop, minimising energy loss in the system.
  • Reliable performance: With no moving parts, pitot tube flowmeters offer reliable performance and long-term stability.

 

Disadvantages:

  • Limited measurement range: Pitot tube flow meters may not be able to accurately measure very low flow rates due to the lack of a high enough pressure differential.
  • Cost-effectiveness compared to thermal mass flowmeters: While pitot tube flowmeters offer reliable performance, they may not be as cost effective as thermal mass flowmeters in certain applications.