📌 Pitot Tube | Insertion Flow Meter

A Pitot tube (also called an Insertion Flow Meter) is a simple, low-cost device used to measure the fluid velocity in pipelines, ducts, or open channels. It works on the principle of differential pressure measurement between stagnation and static pressure points.

🔬 Principle of Pitot Tube

• Based on Bernoulli’s principle:

  • When fluid strikes the open end of the tube (stagnation point), it comes to rest, and pressure increases (stagnation pressure).

  • At the side openings, fluid continues to flow, showing only static pressure.

  • The difference between stagnation and static pressure = dynamic pressure, which is directly related to fluid velocity.

V=2ΔPρV = \sqrt{\frac{2 \Delta P}{\rho}}V=ρ2ΔP​​

Where:

• $V$ = Fluid velocity

• $\Delta P$ = Pressure difference (stagnation – static)

• $\rho$ = Fluid density

⚙️ Construction of Pitot Tube

1. Tube: A slender tube with two openings:

   • Front opening → measures stagnation pressure.

   • Side openings → measure static pressure.

2. Insertion Mechanism: Tube inserted directly into the pipeline or duct.

3. Manometer/Transmitter: Connected to measure the pressure difference.

4. Support Structure: Mounting arrangements for ducts/pipes.

🔄 Working of Pitot Tube

1. Inserted into the pipeline with its front opening facing the fluid flow.

2. The stagnation pressure is sensed at the front opening.

3. The static pressure is sensed from side holes.

4. The pressure difference is measured using a differential manometer or transmitter.

5. Using Bernoulli’s equation, the fluid velocity is calculated.

6. Multiplying velocity by the cross-sectional area of the pipe gives the volumetric flow rate.

🏭 Applications in Pharmaceuticals & Industry

• Measuring air velocity in HVAC ducts.

• Flow measurement in compressed air, steam, and gas lines.

• Monitoring exhaust air in cleanrooms.

• Measuring velocity in large pipelines where installing a full-bore flowmeter is not economical.