Directional control valves can be:

Directional control valves are essential components in hydraulic and pneumatic systems that manage the flow of fluid or air within the system. The correct answer reflects the fact that these valves can indeed be of several types, each serving different applications and functionalities.

Rotary directional control valves operate by rotating a spool or disc to change the flow direction, making them suitable for applications that require precise control. Their design allows for several configurations, providing versatility in directing the flow.

Sliding valves, on the other hand, operate through a sliding motion, often with a spool that shifts position along a cylinder. This sliding mechanism effectively alters the pathways for fluid flow, enabling the control of the system's operations with varying flow paths.

Poppet valves utilize a different mechanism, featuring a movable element (the poppet) that seals against a seat. This type of valve can also direct flow, but it does so by either allowing or blocking fluid passage based on the position of the poppet.

By recognizing that directional control valves can take the form of rotary, sliding, or poppet types, the answer encompasses the full range of common designs used in the industry. Understanding the distinct types of directional control valves helps in selecting the right valve for specific functions within hydraulic and pneumatic systems.