HVAC - EPA Certification Practice Exam

Which of the following statements is true regarding absolute pressure?

1. It can have negative values.

2. 0 psia cannot be reduced further.

3. It is measured in PSIG.

4. It is less important than gauge pressure.

The correct answer is: 0 psia cannot be reduced further.

The statement that "0 psia cannot be reduced further" is true regarding absolute pressure. Absolute pressure is defined as the pressure relative to a perfect vacuum, meaning that 0 psia represents a complete absence of pressure above a vacuum. Because absolute pressure measures how much pressure exists in relation to a vacuum, it cannot physically go lower than 0 psia; negative values would indicate a theoretical pressure state that does not exist in real-world applications. In contrast to gauge pressure, which is measured relative to atmospheric pressure and can have negative values when below atmospheric pressure, absolute pressure always remains a positive value or zero, reflecting the true pressure exerted by a gas or liquid irrespective of the surrounding atmospheric pressure. Thus, other options are not applicable if we are considering the definition of absolute pressure.