Which of the following is NOT an advantage of the manometer?

Asked in SSC JE 09/10/2023 (10am-12pm)

Detailed Explanation

Liquid column manometers are primary pressure-measuring standards. Understanding their engineering advantages and physical limitations is crucial for selecting appropriate instrumentation.

1. Primary advantages of liquid manometers:

High accuracy and sensitivity: Excellent sensitivity for small pressure differences (especially inclined manometers).
Simple and inexpensive construction: No delicate moving mechanical linkages, gears, or electronic sensors.
Direct calibration: Measures pressure directly from fundamental standards (length of liquid column and density: \(p = \rho gh\)).
Suitability for low pressures: Ideal for low-pressure gas and liquid applications where mechanical gauges lack resolution.

2. Key limitations and disadvantages:

Small operating range: High pressures require impractically tall glass columns (e.g., \(100\text{ kPa}\) water requires \(10.2\text{ m}\)).
Fragility: Glass tubes are easily broken under mechanical shock or overpressure.
Need for levelling: Sensitive to orientation and gravitational variation.
No over-range protection: Excessive pressure blows manometric liquid out of the tube.

Why “Small operating range” Is Correct

A small operating range restricts the instrument from measuring high pressures; this is universally classified as a physical limitation and disadvantage of a manometer, not an advantage.

Piezometer and manometer columns: Operating range is physically restricted by tube length.

Why the Other Options Are Wrong

A. Suitability for use in low-pressure applications: Suitability for low-pressure applications is a major advantage where mechanical dial gauges are inaccurate.
B. Better sensitivity: Better sensitivity (particularly with light fluids or inclined tubes) is a well-known advantage of manometers.
C. Simple construction: Simple construction with no moving parts to wear out is a prime advantage of liquid manometers.

Key Point

Small operating range is a limitation/disadvantage of liquid manometers, not an advantage.

Key Concepts for Students

Manometer height scales directly with pressure: h = p / (ρg).
For high pressures, mechanical gauges (Bourdon tube, diaphragm, strain-gauge transducers) are used instead.
Liquid column manometers serve as primary calibration standards for other pressure measuring devices.

Practice more: this is question 3 in Measurement of Pressure MCQs – Part 1. Try the whole set and check every answer instantly.