What is a common function of an air-and-vacuum relief valve in water systems?

An air-and-vacuum relief valve plays a crucial role in maintaining the integrity of water systems by performing dual functions that ensure the system operates smoothly. One of its primary responsibilities is to prevent pressure build-up within the pipelines. When water flows through the system, it can create pressure, especially when there are changes in flow conditions or in the event of pipe blockages. The air-and-vacuum relief valve opens to release excess pressure, thereby protecting the system from potential damage due to over-pressurization.

Additionally, this valve allows air to escape from the system. When water is draining from a pipeline, a vacuum can form, which can lead to pipe collapse or disruption in flow. The air-and-vacuum relief valve automatically opens to let air in and balance the pressure, ensuring that the system remains operational and preventing any negative effects that may arise from a lack of air.

Together, these functions of preventing pressure build-up and allowing air to escape are critical for the safe and efficient operation of water distribution systems. This is why the correct answer encompasses both these essential roles.