A recovery cylinder that is half full of recovered R-12 at normal room temperature will be pressurized to what level?

The correct answer is based on the properties of refrigeration substances, specifically R-12, and how they behave under pressure and temperature conditions. At normal room temperature, which is typically around 70°F (21°C), R-12 has a vapor pressure of approximately 75 psig.

When a recovery cylinder is half full of R-12, the liquid occupies a portion of the cylinder while a vapor space exists above it. The pressure inside this cylinder is determined by the vapor pressure of the refrigerant at the current temperature. Since R-12 is a refrigerant that exists in a phase equilibrium of liquid and vapor, the pressure will stabilize at the vapor pressure corresponding to the temperature in that environment.

At room temperature, the vapor pressure will typically reach a stable level of around 75 psig in a half-full cylinder. This is crucial for recovery processes, ensuring safe handling and adequate storage of refrigerants, as they can exist as both liquid and vapor depending on their pressure and temperature conditions.

Thus, the pressure is primarily influenced by the characteristics of R-12 itself at the ambient temperature, confirming that the correct answer is indeed 75 psig.