Which of the following valves is used for changing the flow direction in a hydraulic system?

A directional control valve is specifically designed to manage the flow path of hydraulic fluid within a system. By using this type of valve, a millwright can direct fluid to different components, allowing for control over the movement of actuators like hydraulic cylinders or motors. This capability is essential in applications where the movement needs to be switched between various directions or functions.

In contrast, a pressure relief valve is focused on protecting the system from excess pressure by allowing fluid to escape when a predefined pressure level is exceeded. A pressure reducing valve is used to lower and maintain fluid pressure to a predetermined level, ensuring that downstream components receive the appropriate pressure for safe operation. An unloading relief valve operates to divert fluid flow back to the reservoir or tank when there is no demand for pressure, but it does not facilitate flow direction changes.

Given these functionalities, the directional control valve is the clear choice for applications requiring flow direction changes in hydraulic systems.