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

A check valve is specifically designed to prevent backflow in plumbing systems, allowing fluid to flow in only one direction. This functionality is essential in maintaining the intended direction of fluid flow and protecting systems from potential contaminants or siphoning effects that can occur if backflow happens. The check valve operates using a disk or flap that opens under pressure from fluid flow in the forward direction and closes when flow attempts to reverse, thereby effectively blocking the backflow.

In contrast, a gate valve is used primarily for on/off control and is not suited for preventing backflow since it can lead to potentially hazardous situations if inadvertently left partially open. A float valve is typically used in applications like filling tanks and manages the water level but does not prevent backflow from occurring. The pressure relief valve serves a different purpose, focusing on relieving excess pressure to prevent system overpressure but does not function as a backflow prevention device. Thus, the check valve is the most appropriate choice for ensuring the integrity of fluid flow direction in plumbing systems.