Frictional Losses at Pipe Fittings

FRICTIONAL LOSSES AT PIPE FITTINGS

Losses occur at the various fittings and valves used in practical systems in addition to the friction losses at the wall of a straight pipe. In general, these losses are derived from sudden changes in the magnitude or direction of flow induced by changes in geometry. They can be classified as loss due to a sudden contraction of enlargement, losses at entrance or exit, and loss due to pipe curvature. Losses can be conveniently expressed as a length of straight pipe offering the same resistance. This is usually in the form of a number of pipe diameters. For example, the loss at a right-angled elbow is equivalent to a length of straight pipe equal to 40 diameters. The sum of the equivalent lengths of all fittings and values is then added to the actual pipe length, and the total frictional loss is estimated by equation (2.20).