In this paper, a one-dimensional, transient theoretical model, the Piston Flow Model (PFM), based on momentum analysis, is proposed to predict the time dependent forces acting on horizontal pipe bends in slug flow. Our experimental apparatus is described and results there from are presented. The PFM has been validated by comparing its predictions with our experimental results for air-water slug flow. The pressure traces, force traces and maximum force predicted agree well with our measurements. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.