An experimental study is conducted to investigate effects of the conical valve angle on thermal energy separation in a counter-flow vortex tube. A new geometry is designed for the cold end side, which is called 'helical swirl flow generator'. Combined and interactive effects of the helical length of the swirl flow generator, the ratio of the tube length to the tube inner diameter (LID), the inlet pressure and especially the angle of the conical valve on the performance of the vortex tube are comparatively investigated as a function of the cold mass fraction, y(c). Four different conical valves have been used with the angle of 30, 45 degrees, 60 degrees and 75 degrees. Finally, it is observed that the effect of the valve angle on the performance changes according to the value of L/D and, it has a weak influence on the system performance. (C) 2010 Elsevier Inc. All rights reserved.