A 3-port valve, also known as a three-way valve, is a type of valve that has three ports or openings for fluid flow. It is typically used to control the direction or flow of a fluid in a system. The three ports are usually labeled as the inlet, outlet A, and outlet B.

The operation of a 3-port valve can vary depending on the design and application, but the basic principle involves the movement of a control element, such as a ball or a disc, to direct the flow of the fluid. In one position, the valve allows fluid to flow from the inlet to outlet A, while blocking flow to outlet B. In another position, the valve allows fluid to flow from the inlet to outlet B, while blocking flow to outlet A. Some 3-port valves may have a third position that allows fluid to flow simultaneously to outlet A and outlet B.

These valves are commonly used in heating, ventilation, and air conditioning (HVAC) systems, as well as in industrial processes where the control of fluid flow is required. They can be manually operated or automated using actuators to provide precise control over fluid direction. The specific application and requirements will determine the type and construction of the 3-port valve used.