If atmospheric pressure is 14.7 psi and gauge pressure is 5 psi, what is the absolute pressure?

If atmospheric pressure is 14.7 psi and gauge pressure is 5 psi, what is the absolute pressure?

• A. 14.7 psi
• B. 5 psi
• C. 9.7 psi
• D. 19.7 psi

Answer: (D)

Absolute pressure is the sum of atmospheric pressure and gauge pressure. Gauge pressure shows how much pressure is above the surrounding air, so to get the total pressure relative to a vacuum, you add them: 14.7 psi + 5 psi = 19.7 psi. The other numbers don’t represent the total pressure: 14.7 psi is just the ambient air pressure, 5 psi is the gauge pressure alone, and 9.7 psi would come from subtracting the gauge from atmosphere, which isn’t how gauge pressure combines. The correct result is 19.7 psi.

Absolute pressure is the sum of atmospheric pressure and gauge pressure. Gauge pressure shows how much pressure is above the surrounding air, so to get the total pressure relative to a vacuum, you add them: 14.7 psi + 5 psi = 19.7 psi. The other numbers don’t represent the total pressure: 14.7 psi is just the ambient air pressure, 5 psi is the gauge pressure alone, and 9.7 psi would come from subtracting the gauge from atmosphere, which isn’t how gauge pressure combines. The correct result is 19.7 psi.