A rotary valve assembly for controlling flow passing through substantially parallel passages, is disclosed. A wall has a cylindrical bore extending transverse to the passages. An elongated rotor is rotatably supported at opposed ends thereof within the cylindrical bore. A plurality of axially spaced valves are disposed on the rotor so as to open and close the passages. A plurality of wall portions are disposed between the valves so as to isolate the adjacent passages. A C-ring is disposed on the respective wall portion of the rotor in sealing contact with the wall surface surrounding the cylindrical bore. An O-ring is disposed axially adjacent to the C-ring and adapted for reducing radial vibration of the rotor and cooperating with the C-ring to prevent leakage flow through the adjacent passages.