Question

Which of the following flow meters works on the principle of pressure difference?

• A. Rotameter
• B. Venturimeter
• C. Pitot tube
• D. Positive displacement meter

Hint:

Logic Tip: Think of a Venturimeter like briefly pinching a garden hose. The restriction forces the water to speed up, which drops the pressure at that specific point. By measuring exactly how much the pressure dropped, engineers can calculate the flow rate.

Answer 1

The Correct Option is B

Concept:
Variable head flow meters calculate fluid flow rate by intentionally introducing a restriction in the flow path and measuring the resulting drop in fluid pressure, relying heavily on Bernoulli's principle.

Step 1: A rotameter is classified as a "variable area" meter. It works by maintaining a constant pressure drop while allowing the physical area of flow to change as a float rises in a tapered glass tube.

Step 2: This type of meter directly measures volume by mechanically trapping, filling, and counting discrete, isolated amounts of fluid. It does not calculate flow based on pressure drops.

Step 3: A venturimeter works by forcing fluid through a gradually narrowing section (throat). As the area decreases, the fluid's velocity increases, which causes a measurable drop in static pressure between the inlet and the throat.

Step 4: While a Pitot tube does use pressure differences (stagnation vs. static pressure), it is primarily used to measure the local velocity at a specific point in a flow. The Venturimeter is the standard industrial answer for a flow meter measuring total volumetric flow rate via the pressure difference principle.