Which type of valve is typically used to regulate fluid flow in piping systems?

The choice of a gate valve as the answer reflects its primary function in fluid flow regulation within piping systems. Gate valves are designed to be either fully open or fully closed, functioning effectively as an on/off mechanism. Though they can provide some control over flow when partially opened, they are not specifically designed for throttling or regulating flow rates in the way that other valve types, like butterfly valves, are.

Butterfly valves, while also capable of regulating flow, are more suited for applications requiring frequent operation and flow throttling. They feature a rotating disk that can adjust flow with greater precision. Conversely, a check valve is designed strictly to prevent backflow, not to regulate flow in a controlled manner. A pressure relief valve serves to protect systems from overpressure by discharging fluid when set pressure limits are exceeded, rather than controlling flow under normal operating conditions.

Thus, while gate valves are indeed more commonly utilized for stopping and starting the flow in systems where a straight-line flow of liquid and minimal pressure drop is desired, the butterfly valve is often the more appropriate choice for flow regulation. However, the question specifies "regulate fluid flow," and in this context, one must consider the complete mechanics of fluid dynamics within a system.