Abstract: An improved low-noise rotary control valve is disclosed. Such valve includes a valve body (10) and a rotatable ball (12) mounted within the valve body. The improvement includes an upwardly extending diverter (28) in the entry flow passage (15) of the valve body (10). A downwardly extending diverter (30) is disposed on the leading edge of the upper half (50) of the valve (12). Such diverters (28, 30) provide only small impedance to flow when the rotary control valve is in the full open position, but provide a tortious path for fluid flow through the valve (20) when it is partially closed. Such tortious path of the fluid inhibits vortex formation within the flow passage of the valve (14) with the result that vibration and noise are reduced. A third impediment placed in the outlet flow passage (16) extends upwardly from the valve and inhibits vortex formation downstream of the valve.