What type of valve is used to prevent backflow in plumbing systems?

The check valve is specifically designed to prevent backflow in plumbing systems. By allowing fluid to flow in only one direction, the check valve effectively blocks any reverse flow that could potentially contaminate the water supply or disrupt the plumbing system's functionality. This mechanism is critical in situations where backflow can occur due to changes in pressure within the system, such as during water mains breaks or pump failures.

Other types of valves, such as the air-admittance valve, are used to allow air into drainage systems to prevent siphoning and protect trap seals, but they do not prevent backflow. Ball valves are primarily used for on-off control within pipes and do not serve the specific purpose of preventing backflow. Pressure relief valves, on the other hand, are designed to release pressure that exceeds a certain threshold to prevent damage to the system, without addressing backflow prevention.