Of the following pressures, which expresses the greatest value?

When comparing pressures, it is important to understand the difference between absolute pressure (PSIA), gauge pressure (PSIG), and standard atmospheric pressure (also often given in PSI). In this context, PSIA represents absolute pressure, which includes atmospheric pressure, while PSIG indicates gauge pressure, measured relative to atmospheric pressure.

The value of 19.7 PSIA is referred to as absolute pressure, which means it includes the weight of the atmosphere pressing down on the point of measurement. The standard atmospheric pressure at sea level is approximately 14.7 PSI. Therefore, when we add this atmospheric pressure to the gauge pressure values, the true total pressure becomes apparent.

For example, the 5 PSIG pressure would convert to absolute pressure by adding atmospheric pressure: 5 PSIG + 14.7 PSI = 19.7 PSIA. However, the values of 7.5 PSI and 14.7 PSI are still lower when considered on their own without converting or adding atmospheric pressure.

In summary, since 19.7 PSIA represents the total pressure including the atmospheric component, it is the highest value in comparison to the other options, which are either lower absolute values or gauge pressures.