The capability of a single impacting tee junction to perform as a full phase separator has been examined. Experimental data were obtained for the limiting inlet conditions under which full separation was attainable using air-water flow at a nominal pressure (P-s) of 200 kPa (abs) and ambient temperature in a junction of inside diameter (d) of 13.5 mm and outlet inclinations (theta) of 2.5 degrees, 7.5 degrees, 15 degrees, 30 degrees, 60 degrees, 75 degrees, and 90 degrees. Flow phenomena near the limiting conditions were observed and a simple correlation based on the similarity between these flow phenomena and the phenomenon of liquid entrainment in small upward branches was developed. This correlation was capable of accurate prediction of the data in terms of magnitude and trend. For high inlet flow rates beyond the limiting conditions, a single tee may not achieve full separation, and multi-junction separators may be necessary for a high degree of separation. (C) 2012 Elsevier Ltd. All rights reserved.