Pressure Measurement — Can Vacuum Pressure Be Read with a Piezometer? Consider a simple piezometer tube (open to atmosphere at the top). Can it be used to measure vacuum (below-atmospheric) pressure at a tapping point in a pipeline?

Introduction:
A piezometer is the simplest pressure-measuring device: a vertical transparent tube connected to the point of interest and open to atmosphere at the top. It is suitable for measuring positive gauge pressure head but has limitations for negative gauge (vacuum) pressures.

Given Data / Assumptions:

• Tube is open to atmosphere at the top.
• Working fluid is incompressible and compatible with the tube.
• No sealing or auxiliary vacuum equipment is used.

Concept / Approach:
In a piezometer, the liquid level rises above the tapping if the pressure is above atmospheric (positive gauge). For vacuum at the tapping, the column would need to fall below the connection level, which an open-topped tube cannot display reliably; air would simply enter, and cavitation or separation can occur. Hence piezometers cannot measure vacuum; manometers with a low-vapor-pressure fluid (e.g., mercury) or vacuum gauges are used instead.

Step-by-Step Solution:
For p > p_atm, height h = (p - p_atm) / (rho * g) is observed as a rise.For p < p_atm, a fall is required; the open top admits air and breaks continuity, preventing a stable negative head reading.Therefore, vacuum pressure measurement needs alternative arrangements (e.g., U-tube manometer or Bourdon-type vacuum gauge).

Verification / Alternative check:
Standard textbooks explicitly restrict piezometers to positive gauge measurements and recommend U-tube or inverted manometers for vacuum readings.

Why Other Options Are Wrong:
Sealing with a pump changes the instrument type; arbitrary small limits (< 1 kPa) are unsupported; the correct general statement is that a simple piezometer cannot measure vacuum.

Common Pitfalls:
Connecting piezometers where vapor pressure may be approached; assuming any negative reading is meaningful; ignoring capillary effects in very small tubes.

Final Answer:
False