What is the primary function of a pressure relief valve?

The primary function of a pressure relief valve is to prevent overpressure conditions within a system. This is crucial because excessive pressure can lead to equipment failure, dangerous leaks, or catastrophic explosions. The valve opens automatically when a pre-set pressure is exceeded, allowing fluid to escape and relieving the pressure in the system, thus ensuring safe operation.

While controlling fluid flow, ensuring system efficiency, and measuring pressure changes are important aspects of fluid systems, these are not the main purpose of a pressure relief valve. The valve's design specifically targets the mitigation of risks associated with high pressure, making option B the most accurate choice.