Hypothesis: In this study, the spontaneous and forced imbibition of an asymmetric Y junction by a completely wetting fluid submitted to the action of gravity is investigated. The considered junction is made of three capillaries of close but different dimensions. This system is used as a simple model to study gravity induced fluid fragmentation in microfluidic junctions and porous media. Using simple calculations, analytical results predict a fragmentation criterion, two dynamics leading to fluid fragmentation and asymptotically drop lengths and spacings. Experiments: Both spontaneous and forced imbibitions of three microfluidic Y junctions were undertaken, varying the capillary and Bond numbers. Results show the validity of the fragmentation criterion, the derived junction imbibition dynamics and confirm qualitatively the analytical description of the fragmentation process. Findings: The dynamics prior to fragmentation does not depend on whether the imbibition is forced or spontaneous. However, it depends on the position with respect to gravity of the junction branch of lowest Laplace pressure. Finally, gravity induced fragmentation happens in the squeezing regime described in the Drop-On-Demand (DOD) literature at the junction and is locally controlled by viscosity rather than gravity. (C) 2018 Elsevier Inc. All rights reserved.