Devices and systems which control the flow of fluid through a conduit are described herein. One flow control device that controls the flow of fluid through a conduit, includes a body having an axis and defining a passage that allows fluid to flow from an upstream position to a downstream position, the valve body having a converging portion in the upstream position with an inner surface that curves gradually inward, but having an annular rim formed by a portion that extends outward from the inward curving shape, and a throat between the converging and diverging portions; and, a flow regulator supported within the body for controlling the flow of fluid through the conduit, the flow regulator having an annular seating surface configured to contact the annular rim of the body.