This paper proposes a specially designed splitting device to study the phase separation of gas-liquid two-phase flow through a small break. The inner pipe diameter of the main test section is 40 mm. A small hole with 2.5 mm diameter was drilled at the main pipe wall to simulate the break. Three break orientation angles were tested, including 0 degrees (side), -45 degrees (inclined) and -90 degrees (bottom) from horizontal orientation. Experiments were conducted in an air-water two-phase flow loop with a horizontal test section. Stratified wavy, annular and slug flows were observed. Experimental results show that phase separation is affected by the break location, flow pattern and gas and liquid superficial velocities. The fraction of liquid taken off of slug flow is observed much larger than that of stratified wavy or annular flows due to its particular flow behavior. A simplified correlation of break pressure difference is proposed in terms of break outlet mass flow rate and gas quality. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.