Which type of valve allows flow in one direction but prevents backflow?

A check valve is specifically designed to allow fluid to flow in only one direction while preventing any backflow. This function is essential in various systems to maintain pressure and protect equipment from potential damage caused by reverse flow.

Check valves achieve this through a simple mechanism that typically involves a disc or a ball that swings or lifts off its seat when fluid flows in the designated direction. If the flow attempts to reverse, the disc or ball reseats and blocks the opening, thereby stopping the backflow effectively.

While other types of valves serve various functions, such as controlling flow rates or directing flow paths, they do not provide the same backflow prevention feature inherent to check valves. For example, a ball valve can control flow very effectively, but it does not inherently prevent backflow unless specifically designed with that capability. Similarly, lift check valves also function to allow flow in one direction and are a variation of check valves, but they are less common than standard check valves in many applications.

In summary, the defining characteristic of the check valve is its primary role in preventing backflow, making it the correct answer to the question.