The production of metal powder using gas atomization technique is a wide spread process for manufacturing a wide range of spherical metal powder alloys. Metal powder properties generally improve with smaller powder particle size. Close-coupled atomizers are of great interest and controlling their performance parameters is critical for metal powder producing industries. In this study a new designed close-coupled nozzle system was used to produce tin powder to investigate the effect of the protrusion length of the melt delivery tube on the pressure formation at the melt tip. Observed improvement in particle refinement cannot be directly attributed to an increase in atomizing pressures and gas kinetics. Results from this study indicated that the observed metal flow rate was not behaving as what was earlier assumed, namely that, deeper aspiration enhanced metal flow rate. The melt flow rate was reduced with increasing the atomizing gas pressure. So that gas to melt mass flow ratio was increased for the same protrusion length and this ratio increase caused the finer powder particle size. (c) 2006 Elsevier B.V. All rights reserved.