Which of the following can be used to control actuator speed?

The needle valve is specifically designed for controlling the flow rate of fluids in hydraulic systems, which in turn affects the speed of actuators. By adjusting the position of the needle, the flow can be increased or decreased, allowing for finer control over the actuator's speed. This is especially important in applications that require precise movement, such as in robotics or automated machinery, where speed adjustments can significantly influence performance and safety.

While other types of valves can play roles in fluid systems, they do not offer the same level of control over flow rates as a needle valve. For example, a shuttle valve directs flow in specific paths but does not regulate the flow rate. A check valve allows fluid to flow in only one direction and prevents backflow, offering no means for adjusting flow speed. Similarly, a ball valve is great for on/off control of fluid but lacks the capacity for fine flow regulation. Hence, the needle valve stands out as the most effective option for controlling actuator speed.