Which of the following is typically used in plumbing to indicate flow direction?

The check valve is specifically designed to allow fluid to flow in one direction while preventing backflow. This functionality is essential in plumbing systems, especially in applications where it is crucial to maintain the correct flow direction, such as in waste systems, fuel lines, and water systems. The orientation of the check valve is typically marked with an arrow indicating the direction of flow, making it straightforward to install and ensuring that users understand how the fluid should pass through the system.

In contrast, while flow meters are used to measure the flow rate of liquids or gases, they do not necessarily indicate the flow direction. Pressure gauges measure the pressure of a fluid within a system and lack the capability to specify flow direction. Ball valves control the flow of liquid or gas but are not primarily used for indicating direction; rather, they are used to either start or stop the flow entirely. Thus, the check valve is uniquely suited for this function within plumbing systems.