The development and evaluation of a new type of flow conditioning system between the control valve and stilling chamber of the Vought Systems Division 4 X 4-ft transonic-supersonic wind tunnel are reported. The new system results in a series of normal shocks created by four perforated plates to dissipate total pressure differences between the reservoir and stilling chamber. Data are presented which demonstrate flow quality improvements obtained by using the new design, including a significant reduction in test section flow unsteadiness and elimination of flow angularity induced by the control valve at transonic Mach numbers. Design methods are developed which insure no loss in run time at transonic Mach numbers and minimum run time losses at higher supersonic Mach numbers.