Which device can be used to prevent backflow in a plumbing system?

The prevention of backflow in a plumbing system is critical to ensure the safety and quality of the water supply. An air gap is a highly effective method for preventing backflow because it creates a physical separation between the water supply and potential contaminants. This separation is achieved by allowing a gap between the outlet of a fixture and the flood level of the receptacle into which it drains.

When water flows from a fixture, it does so without any physical connection that could allow for backflow to occur. If there is a sudden drop in pressure within the system, contaminants cannot be siphoned back into the potable water supply due to this air gap. This is crucial in preventing situations that could lead to cross-contamination, thereby safeguarding public health.

In contrast, pressure relief valves, flow control valves, and trap seals serve different functions within a plumbing system. Pressure relief valves are designed to release excess pressure in systems, flow control valves regulate the flow rate of liquids, and trap seals are meant to maintain a water barrier against sewer gases, but none of these devices specifically address the prevention of backflow in the same way that an air gap does.