Comparative Study of Pressure Reducers for Aerosol Sampling from High Purity Gases

A performance evaluation and comparative study has been conducted with six pressure-reducing devices suitable for particle sampling from high pressure gas systems. Pressure-reducing devices are used to reduce the gas pressure from that existing in the high-purity compressed gas system to ambient conditions for subsequent measurement of particulate contaminants by particle counters. Six pressure-reducing devices, including designs based on the orifice plate, orifice design with expansion cone, and capillary tube designs, have been evaluated experimentally to determine their particle penetration characteristics and contribution to background particle. Studies showed that particle loss in pressure reduc· ers depended upon the pressure-reducing geometry, gas pressure and particle size. Particle penetration through orifice type devices was found to be superior to that found for capillary tube type devices. The 50% penetration through orifice type pressure reducers was found to be at a particle diameter of approximately 3.0 ",m, while for the capillary tube designs at a particle diameter less than 1.0 ʹ" m. For the orifice-type pressure reducers the particle background concentration was less than 0.05 particles/ft3 (1.77 particles/m3 ). Significantly higher particle background levels were found for the capillary tube type devices which is believed to result from particle reentrainment from the capillary tube wall