What does a pressure reducing valve primarily do?

A pressure reducing valve is primarily designed to lower and regulate the pressure of a fluid (typically gas or liquid) from a higher source pressure to a lower, more usable pressure suitable for a system. The selected answer accurately reflects this fundamental purpose, as the valve takes the city main pressure, which is often much higher, and reduces it to a safe and manageable working pressure that ensures efficient operation without risking damage to the downstream equipment or appliances.

Other options do not align with the primary function of a pressure reducing valve. While relieving system pressure relates to safety measures, it does not encompass the core function of reducing pressure for operational use. Similarly, reducing working pressure to match the city main pressure misunderstands the action of the valve, as the valve's role is to convert high pressure into a lower working pressure rather than vice versa. The prevention of hot water gravity circulation pertains more to check or control valves, not to the function of a pressure reducing valve, which focuses specifically on managing pressure levels.