The forward and reverse flow characteristics have been measured for Zobel type vortex diode with 19 mm throat diameter using superheated stea with inlet pressures up to 12 bar absolute, and exhausting into a subatmospheric condenser to achieve inlet to outlet pressure ratios up to 30 A discharge factor, Cf, which relates the measured mass flow rate to the theoretical mass flow rate of a critical flow through a comparable isentropic nozzle, has been used to describe the resistance of the diode. In the choked region of the forward and reverse flow, Cf has a constant value of 0.95 and 0.38 respectively. The critical pressure ratios in the forward and reverse flow are approximately 2 and 4. Repeating the tests using wet steam with known dryness fractions, ha shown separately the effects of wetness on the diode performance. The forward flow discharge factor in the choked condition is seen to be independent of dryness fraction, and found to lie between 0.9 and 1.0, which is similar to that found with superheated steam. The reverse flow discharge factor in the choked condition varied from about 0.4 for a dryness fraction of, 0.98, to 0.48 for a dryness fraction of 0.92. Excessive steam wetness (quality less than 0.93) in the reverse flow direction led to a build-up of water and when this was eventually swept through to the diode, the resistance was seen to fall substantially as th strong internal vortex was destroyed. This problem can be overcome in practice, however, by installing a water separator before the diode. Reverse flow characteristics of four 10 mm throat diameter Zobel typ vortex diodes have been measured using air with inlet pressure up to 31 bar absolute, and exhausting into atmosphere. The characteristics are seen to be similar to those found with superheated steam, with a value of Cf of 0.38. The effect of installing the four diodes in series was investigated. It was shown that by sharing the pressure drop between the diodes and moving the operating point into the incompressible regime, som of the high resistance performance could be recovered. A detailed study of vortex flow was carried out using a large vortex throttle with superheated steam as the working fluid. The static pressur distribution has been determined experimentally both across the vortex an along the axis of the chamber exit duct. The chamber internal wall temperatures have been obtained using insulated, flush-mounted thermocouples. The measurements enabled the velocity field to be calculated. The bulk of the internal vortex was found to have an exponer. of 0.69. It was found that the vortex throttle choked at an upstream to downstream pressure ratio of about 6 with corresponding Cf value of 0.28. The resistance of vortex chambers is known to be strongly influenced by the presence of reversed flow in the exit, due to vortex breakdown. Schlieren photography of the swirling exhaust flow was used to show that whilst vortex breakdown does occur, it can only do so after the flow has become subsonic downstream of the exit and cannot therefore influence the vortex chamber resistance.