The flow throttling and regulating function of a valve means the valve can control the flow capacity, pressure, flow speed etc. Simply speaking,the flow throttling& regulating function let you throttle the fluid depending open % of the total opening. Lesser the opening higher the throttling and otherwise.
Such function valves can control the speed and capacity of flow, temperature, or pressure in a piping system. The valves can be moved into any position, including fully opened and fully closed (similar function with Shutoff/On valve). They can be operated with a manual hand wheel or can be driven with an automated actuator. The regulating valves are responsible for varying the valve’s position to maintain constant pressure downstream. The regulator opens and closes to increase or decrease the pressure in the system.

Pressure Regulating Valve

Regulating Knife Gate Valve

Throttling-V-Port-Valve