To measure static pressure in a pipe, one uses a pressure gauge connected to a:
Try it first: pick an option, then read the explanation.
Correct answer: D. Manometer
Asked in SSC JE 2010
Detailed Explanation
Static pressure in a flowing fluid is measured using an instrument connected flush to the pipe wall without protruding into the fluid stream.
1. Evaluate the functions of the listed devices:
- Pitot tube: Measures stagnation pressure (\(p_0 = p + \frac{1}{2}\rho v^2\)) at its tip facing upstream.
- V-notch: Used to measure discharge (flow rate) in open channels, not pipe pressure.
- Differential U-tube: Measures the difference in pressure between two points, not static pressure at a single point.
- Manometer (Piezometer / Simple U-tube): Measures the static pressure at a cross-section when connected to a wall tapping.
Why “Manometer” Is Correct
Among the given options, a manometer (or piezometer) connected to a pipe wall tap is the standard instrument used to measure the static fluid pressure.
Why the Other Options Are Wrong
- A. Pitot tube: A Pitot tube measures dynamic and stagnation pressure, not pure static pressure alone.
- B. V–notch: A V-notch weir is an open channel flow-rate measuring device.
- C. Differential U-tube: A differential U-tube measures the difference in pressure between two points, not local static pressure at a point.
Key Point
A manometer connected to a wall pressure tap measures static pressure in a pipe.
Key Concepts for Students
- A wall tap senses pure static pressure because fluid streamlines are undisturbed.
- Connecting a U-tube manometer allows measurement of both positive and vacuum static pressures.
- Static pressure is the true thermodynamic pressure felt by particles moving with the flow.
Practice more: this is question 18 in Measurement of Pressure MCQs – Part 2. Try the whole set and check every answer instantly.