LIT194-Handbook of TII.pdf - Diamond Head Sprinkler Supply

Total Dynamic HeadTotal Dynamic Head is the amount of pressure that one pump must generate or be availablefor proper sprinkler system operation. It represents the total of all pressure losses and requirementsincluding: 1) pressure change due to elevation, 2) sprinkler operating pressure, 3) friction loss inpipes, fittings and valves and 4) the pressure required to move the water.TDH =H s + H p + h f + H vWhere:TDH = Total Dynamic Head is the maximum pressure the pump will be required togenerate.H s = Static Head, the vertical distance in feet from the surface of the water source tothe point of discharge, in feet.H p = Pressure Head, the pressure required at the discharge (sprinkler, emitter ordischarge pipe) in feet. (If sprinkler psi is used it must be multiplied by 2.31 toconvert to feet.)h f = Friction Head, the pressure lost due to friction in pipe, valves and and fittingsfrom the water intake to the discharge point, in feet. (If pressure loss iscalculated in psi, it must be multiplied by 2.31 to convert to feet.)H v = Velocity Head, the energy required to move the water at the intended velocity(see velocity head) in feet. Because this is an insignificant loss in Total DynamicHead, it is sometimes ignored in these calculations.Example:Determine the Total DynamicHead where the sprinkleroperating pressure is 50 psi, themaximum flow is 150 gpm, theintake line is 35 ft. long andthe discharge line is 450 ft. Thepressure loss in the foot valveat that flow rate is given by themanufacturer to be 1 psi. In thissample problem we ignore thepressure loss in fittings.90 ft.4 in. Class315 PVC6 ft.4 in. Class315 PVCPumpFootValveMinimumWaterLevelTDH =H s + H p + H f + H vTDH = (90 + 6) + (50 x 2.31) + [(35 + 450) x ( 0.66 ) x 2.31] + (1 x 2.31) + 4.16 2100 64.4TDH = 221.47 ft.®Handbook of Technical Irrigation Information21