How does a boiler operator determine the absolute pressure?

To determine the absolute pressure, it is essential to understand the relationship between gauge pressure, which is the pressure indicated by the gauge on the boiler, and atmospheric pressure. Gauge pressure reflects only the pressure above atmospheric pressure. Absolute pressure, on the other hand, is the total pressure exerted, which includes both the gauge pressure and atmospheric pressure.

The correct method for calculating absolute pressure is to add the gauge pressure to the atmospheric pressure because absolute pressure is defined as:

Absolute Pressure = Gauge Pressure + Atmospheric Pressure

This ensures that all forces acting on the fluid within the boiler are accounted for, which is vital for safe operation and efficiency. Gauge pressure alone would not provide a complete picture because it does not consider the baseline atmospheric pressure.

Thus, the answer, which involves subtracting the gauge pressure from the atmospheric pressure, would lead to an incorrect understanding of how pressure measurements work, as it misrepresents the basic principle of pressure measurement in relation to atmospheric conditions. The other options similarly reflect misunderstandings about the relationship between gauge and absolute pressures.