Irrigation Professionals with questions about ... - Hunter Industries

LENGTH is the fourth factor affecting friction losses in pipe. Thegreater the distance, the greater the cumulative effect of the first threefactors (velocity, i.d. and roughness). In Figure 17 we see the directrelationship between increased length and increased pressure loss. Thetotal pressure loss doubles as the length of the pipe doubles.Figure 17These four factors affecting pressure loss in pipe were used to developformulas for calculating the pressure loss associated with various types ofpipe. Several formulas were developed; the most common in landscapeirrigation hydraulics is the Hazen-Williams formula. The Hazen-Williamsformula can be represented as:1.852 1.852100 QH f = 0.090194( )4.866C dWhere H f= pressure loss in pounds per square inch (PSI)C = roughness factorQ = flow in gallons per minute (GPM)d = inside pipe diameter in inchesSince these formulas are somewhat cumbersome, we will rely on chartsdeveloped using the Hazen-Williams formula. Samples of these charts canbe found in the back of this design manual.