Irrigation Professionals with questions about ... - Hunter Industries

1. Look in the left column (FLOW G.P.M.”) on the friction loss chartand read down to the GPM in our sample.Sample Problem:6 GPM2. Now, read across the top of the chart looking for the size ofthe pipe in our sample problem.Sample Problem:3/4 in .3. Read down this column, under the “P.S.I. LOSS” heading,and across the row for the GPM.Sample Problem:1.67 PSI loss4. Where the two intersect (in Step 3) is the PSI loss per 100. Dividethis number by 100 to find the loss per foot.Sample Problem:1.67100= 0.0167 psi loss per ft.5. Multiply your answer by the length of pipe supplying thissprinkler only (just to the next head on the zone).Sample Problem:0.0167 x 42 ft. = 0.701Determining Dynamic Pressure LossesWhen calculating dynamic pressures in pipes, we use the followingfactors:A) Pressure change due to elevation change.B) Pressure loss due to friction losses in the pipeC) Pressure losses in valves, meters, etc. (These losses are determinedby the manufacturer and listed in product literature or technicalcharts.)D) Pressure losses due to fittings.The following example illustrates how the dynamic pressure at a givenpoint in a landscape irrigation system is determined. Pressure change dueto the change in elevation is calculated and the friction losses aresubtracted from the subtotal. The example uses the Friction Loss Charts atthe back of this design manual.