What device would you use to control hydraulic fluid flow?

A hydraulic valve is the correct choice for controlling hydraulic fluid flow. Hydraulic valves are specifically designed to manage the direction and rate of fluid within a hydraulic system. They work by opening, closing, or regulating the flow paths of the hydraulic fluid, allowing the operator to manipulate system performance effectively.

These valves can be manually operated, solenoid-actuated, or automatically controlled, depending on the application and requirement. By adjusting the position of the valve, one can increase or decrease flow, direct the fluid to different parts of the system, or stop the flow altogether, which is essential for controlling actuators, motors, or any other hydraulic components connected in the system.

Other devices mentioned in the question, such as a hydraulic accumulator, hydraulic cylinder, and hydraulic reservoir, play different roles in a hydraulic system. An accumulator stores hydraulic energy for later use, a cylinder converts hydraulic fluid energy into mechanical work, and a reservoir serves as a storage tank for the hydraulic fluid. None of these devices are designed to directly control fluid flow in the manner that hydraulic valves do.