Gauge pressure is the pressure in excess of which reference pressure?

• A. Absolute Pressure
• B. Atmospheric Pressure
• C. Pressure Differential
• D. Working Pressure

Answer: (B)

Gauge pressure is the pressure in excess of the surrounding air pressure. In everyday instruments, the baseline is atmospheric pressure, so the reading shows how much the system pressure rises above ambient air. For example, if atmospheric pressure is about 14.7 psi and a gauge reads 30 psi, the absolute pressure inside the system is 44.7 psi (P_abs = P_gauge + P_atm). The absolute pressure is referenced to a vacuum, not to atmosphere, so it would be higher than the gauge reading by the amount of atmospheric pressure. Differential pressure is simply the difference between two pressures, not a single reference; and working pressure is a design limit, not a reference pressure.