ESDU 83037 gives comprehensive data for the estimation of pressure loss in circular-arc bends taking account of the effects of bend radius ratio and angle, upstream and downstream duct lengths, surface roughness, cross-sectional shape and Reynolds number. The data are in the form of a general equation for which a graphical solution is also provided. For the common case of a 90 degree, smooth bend of circular or square section a direct graphical presentation of pressure loss coefficient is given. Reanalysis of the available information for single and 90 degree composite mitre bends has shown that, contrary to the usual assumption, surface roughness has a significant effect on pressure losses. These data are given graphically in terms of a reference pressure loss coefficient and correction factors for Reynolds number and roughness effect. Approximate data are provided for "standard pipe bends" for use where little detail of the bend geometry is available and sources of data for other bend types (for example, bends where the inner and outer walls are not concentric) are referenced. The effect of guide vanes or splitters in bends is considered and a simple design for use in mitre bends is given. All the information results from correlations of experimental data drawn from a wide range of sources. A practical worked example is included, and data on straight pipe friction factors and effective surface roughness of various pipe materials are given. The method for circular-arc bends is provided in the software volume as a program on disc accessible under DOS, both as uncompiled Fortran and in ESDUview, a user-friendly shell that prompts on-screen for input data.