Which one of the following is a difference between a typical relief valve and a typical safety valve?

Correct Answer: Option C — A relief valve gradually opens as pressure increases above set point pressure whereas a safety valve fully opens at the set point pressure.

Relief valves are designed for liquid service and open proportionally to the pressure increase above the set point. Conversely, safety valves are designed for compressible fluids like steam, utilizing a huddling chamber to achieve a 'pop' action, ensuring full opening at the set pressure to prevent overpressurization.