Abstract—We analyze the influences of initial conditions on a diaphragmless shock tube operation. The system consists of a driver tube, driven tube, and damp tank. The driver tube has a circular cross section with a diameter of 150 mm, while the driven tube has a rectangular cross section (60 mm × 150 mm). The shock tube is operated using a quick-opening pneumatic piston. Two types of piston driver are employed to release the pressure inside the piston: small diaphragm and solenoid valve types. The effect of the piston driver type on the shock Mach number is evaluated. Moreover, the initial piston pressure is chosen as a parameter to investigate its effects on the shock Mach number. The shock Mach number is determined by not only the initial operational pressure ratio of the shock tube but also the initial pressure in the high-pressure section in the diaphragmless shock tube. For a range of initial piston pressures, the shock Mach number is almost constant under a constant initial operational pressure ratio.