HVAC - EPA Certification Practice Exam

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What does absolute pressure measure in comparison to gauge pressure?

It is measured above atmospheric pressure
It includes all atmospheric pressure
It is lower than gauge pressure
It is the same as atmospheric pressure

The correct answer is: It includes all atmospheric pressure

Absolute pressure measures the total pressure exerted by a fluid, including all atmospheric pressure acting on it. This means that when measuring absolute pressure, the measurement accounts for the weight of the atmosphere above the point being measured. In contrast, gauge pressure measures pressure relative to the ambient atmospheric pressure, effectively excluding atmospheric pressure in its calculations. For example, if a tire pressure gauge reads 30 psi, this figure typically represents gauge pressure, meaning that it’s measuring the pressure above the current atmospheric pressure. If atmospheric pressure is considered, the absolute pressure of the tire would be about 30 psi plus the atmospheric pressure (approximately 14.7 psi at sea level), resulting in an absolute pressure of around 44.7 psi.