INTRODUCTION With two bends in series the overall pressure loss is not obtained by summing the individual bend losses unless the spacing between the bends is sufficiently large to eliminate interference effects (see Table 11.2). This Item gives values of a correction or interaction factor@ ?? that relate the overall loss of combinations of two bends in series to the sum of the losses for the individual bends in interference-free flow. The types of bends considered in this Item are circular arc and mitre@ both of constant cross-sectional area. A further subdivision of mitre bends into either single mitre or composite types is made. The geometries of the three types of bends are shown in Sketches 1.1 to 1.3. For a particular combination of bends the interaction factor