Definition check — vacuum pressure vs. atmospheric pressure When pressure intensity at a point is lower than local atmospheric pressure, the difference (p_atm − p_local) is called vacuum pressure. Do you agree?

Introduction / Context:
Pressure terminology in hydraulics distinguishes among absolute pressure, gauge pressure, and vacuum pressure. Understanding these definitions is essential for instrumentation, cavitation analysis, and pump selection.

Given Data / Assumptions:

• Local atmospheric pressure head h_atm is known.
• Measured local absolute pressure head h_abs may be above or below h_atm.
• We adopt standard sign conventions used in hydraulics.

Concept / Approach:
Gauge pressure p_gauge = p_abs − p_atm. When p_abs < p_atm, p_gauge is negative. The magnitude of this negative gauge pressure is termed vacuum pressure: p_vacuum = p_atm − p_abs. In head terms: h_vacuum = h_atm − h_abs.

Step-by-Step Solution:

Verification / Alternative check:
Manometers with one leg open to atmosphere read vacuum as an upward deflection on the vacuum side; the magnitude equals p_atm − p_abs. This matches the definition above.

Why Other Options Are Wrong:

• Disagree / qualifiers: Vacuum pressure is not limited to gases or cavitation; any fluid at p_abs < p_atm qualifies.

Common Pitfalls:
Confusing absolute and gauge scales; forgetting that absolute pressure cannot be negative (lower bound is zero absolute).

Final Answer:
Agree