HVAC - EPA Certification Practice Exam

How is atmospheric pressure displayed on a gauge pressure measurement?

1. As absolute pressure

2. As negative PSI

3. As zero PSI or PSIG

4. As a percentage of atmospheric pressure

The correct answer is: As zero PSI or PSIG

The correct response indicates that atmospheric pressure is represented as zero PSI or PSIG on a gauge pressure measurement. Gauge pressure measures pressure relative to atmospheric pressure, meaning that the zero point on a gauge is defined as the ambient atmospheric pressure. Therefore, any pressure reading above this zero point is considered positive, while any reading below it is negative. In the context of pressure gauges, this means that if the gauge is at zero PSI or PSIG, it implies that the pressure being measured is exactly equal to the surrounding atmospheric pressure. This is a standard convention in pressure measurement systems, allowing for consistent interpretations of readings. When a gauge shows pressure above zero, it signifies that the measured pressure exceeds atmospheric pressure, and when it shows negative values, that indicates a vacuum or lower pressure than the atmospheric baseline. Thus, measuring relative to atmospheric pressure is essential in many applications, including HVAC systems, to ensure accurate monitoring and control of pressure conditions.