What is a characteristic of a check valve?

A check valve is specifically designed to allow fluid to flow in one direction only. This unique characteristic prevents backflow, ensuring that the fluid moves in the intended direction through a system or pipeline. The operation of a check valve relies on the pressure of the fluid; when the flow is in the correct direction, the valve opens, and when the flow reverses, the valve closes due to the back pressure, completely blocking the reverse flow. This feature is essential in various applications to protect equipment from potential damage caused by backflow, such as in pumps and fluid systems.

The other options describe functionalities not inherent to check valves. While some may control multiple outputs or require manual intervention, these functions are typically associated with other types of valves, such as gate valves or globe valves, which are designed for different operational purposes. Moreover, maintaining constant pressure is generally the role of pressure relief valves or regulators, rather than check valves, which are focused solely on preventing backflow.