The handbook of Technical irrigaTion informaTion - Hunter Industries

Handbook of Technical Irrigation Information4 inch Class 315 PVC6 feetFootValveMinimumWaterLevel18NPSHA = 30 – 6 – (1.5 x 2.31) – ( 0.31 x 0.2 x 2.31) – (0.5 x 2.31)NPSHA = 19.24 feet of headThe Net Positive Suction Head Available (NPSHA) can be calculated by the formula above while the Net PositiveSuction Head Required (NPSHR) varies from one pump model to another and can be found with the pump performancecurves provided by the manufacturer. For any given pumping situation and pump model, the NPSHA mustexceed the pump’s NPSHR in order for the pump to operate properly and avoid cavitation.Total Dynamic HeadTotal Dynamic Head is the amount of pressure that one pump must generate or be available for proper sprinklersystem operation. It represents the total of all pressure losses and requirements including: 1) pressure change due toelevation, 2) sprinkler operating pressure, 3) friction loss in pipes, fittings and valves and 4) the pressure required tomove the water.TDH = H s + H p + h f + H vWhere:TDH = Total Dynamic Head is the maximum pressure the pump will be required to generate.H s = Static Head, the vertical distance in feet from the surface of the water source to the point of discharge,in feet.H p = Pressure Head, the pressure required at the discharge (sprinkler, emitter or discharge pipe) in feet.(If sprinkler PSI is used it must be multiplied by 2.31 to convert to feet.)h f = Friction Head, the pressure lost due to friction in pipe, valves and and fittings from the waterintake to the discharge point, in feet. (If pressure loss is calculated in PSI, it must be multiplied by2.31 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 Dynamic Head, it is sometimes ignored inthese calculations.