HEAD LOSSFluid FlowMinorLossesThe losses that occur in pipelines due to bends, elbows, joints, valves, etc. are sometimes calledminor losses. This is a misnomer because in many cases these losses are more important thanthe losses due to pipe friction, considered in the preceding section. For all minor losses inturbulent flow, the head loss varies as the square of the velocity. Thus a convenient method ofexpressing the minor losses in flow is by means of a loss coefficient (k). Values of the losscoefficient (k) for typical situations and fittings is found in standard handbooks. The form ofDarcy’s equation used to calculate minor losses of individual fluid system components isexpressed by Equation 3-15.(3-15)H_{f}k^{v}22gEquivalentPipingLengthMinor losses may be expressed in terms of the equivalent length (L_{eq}) of pipe that would havethe same head loss for the same discharge flow rate. This relationship can be found by settingthe two forms of Darcy’s equation equal to each other.fL v^{2}D 2 gkv^{2}2 gThis yields two relationships that are useful.(3-16)L_{eq}k^{D}f(3-17)kfL_{eq}DTypical values of L_{eq}/D for common piping system components are listed in Table 1. Theequivalent length of piping that will cause the same head loss as a particular component can bedetermined by multiplying the value of L_{eq}/D for that component by the diameter of the pipe.The higher the value of L_{eq}/D, the longer the equivalent length of pipe.HT-03 Page 34 Rev. 0

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