Book - School of Science and Technology

Water systems - principles 23510.052Velocities in m/s0.5 1.01.52.02.01.51.035 28 221.20.8151210Pipe size in mmWater flow rate in energy units kW/K1.00520.100.20.11.10.80.40.30.60.40.30.20.60.40.30.25.08650.220.10.1Units at pointsthus areequivalent lengthsin metres for ζ =10.01102 5 10 22 5 10 32 5 10 42 5Pressure loss in Pa per metre run (palm)10 5Figure 9.2 Sizing chart in energy units (kW/K) for water flow at 75 C in copper pipes (BS 2871: Table X)A convenient way of making allowance for single resistances is to add to themeasured length of straight pipe an equivalent length (EL) for each such item. Valuesfor unit equivalent length are marked on the charts in Figures 9.1 and 9.2 and these,multiplied by the appropriate value of , provide the actual equivalent length to beadded. The Guide Section C4 lists hundreds of values of for various types of pipefitting, etc., but Table 9.1 provides a short summary adequate for approximate calculationsto suit most normal situations.VelocitiesExperimental data regarding acceptable maximum and minimum water velocities in pipesare meagre but there seems to be general agreement that erosion is unlikely to become aproblem at less than about 2.5±3 m/s: similarly, it has been suggested that velocities of less