A fluid flow control device includes a valve body, a bonnet, a control assembly, and a seal assembly. The valve body defines an inlet portion, an outlet portion, a bonnet opening, and a fluid flow path extending between the inlet portion and the outlet portion. The bonnet is disposed in the bonnet opening. The control assembly is at least partly supported by the bonnet, and includes a ball element disposed within the valve body and rotatable between an open position and a closed position. The valve body defines an internal recess at a location downstream from the inlet portion and adjacent the bonnet opening. The seal assembly is disposed within the internal recess and includes a movable sleeve seal, a retaining device, and one or more sealing elements for preventing leakage between the sleeve seal and the retaining device and/or the valve body.