A flow control valve is a combination of a __________.

A flow control valve is designed to regulate the flow of fluid by using the mechanisms of a needle valve and a check valve. The needle valve component allows for precise adjustments in flow rate by changing the size of the opening through which the fluid passes. This precision is crucial in applications where controlling the speed and pressure of fluid flow is important.

The check valve aspect ensures that fluid flows in only one direction, preventing backflow that could disrupt system operation or cause damage. This combination is effective in maintaining desired flow characteristics while also protecting the system from potential issues related to reverse flow.

In contrast, options involving other types of valves, such as relief valves or directional control valves, do not encapsulate the essential functions of a flow control valve as accurately as the combination of a needle valve and a check valve. Therefore, the choice that identifies a flow control valve as a blend of a needle valve and a check valve best represents its operational purpose in fluid systems.