Variable port valve plug

A valve assembly has a valve body having an inlet passageway and an outlet passageway. A flow orifice is disposed within valve body and provides flow communication between the inlet passageway and outlet passageway. A valve seat cooperates with the flow orifice and a variable port valve plug to open and close the valve. The valve plug has a plug body with a conically-shaped smooth tapered wall, a proximal end, and a domed distal end surface that smoothly transitions into the tapered wall. The valve plug is movable between an open position out of contact with the valve seat and a closed position borne against the valve seat. A maximum open position of the valve plug relative to the valve seat can be selectively changed to vary flow characteristics through the valve assembly.