An Assessment for Hydraulically Efficient Design of Uniformly Sloping Submain Lines

Abstract

Determining the actual pressure head profiles along the submain lines with a uniform slope is very important for proper hydraulic design of water distribution systems. In practice, there are three general pressure head profiles (Type I, Type II, and Type III) along submain lines depending on different uniform line slope situations. Of all types of pressure profiles, the Type IIb profile is considered the optimal (or ideal) pressure profile which can produce the minimum pressure head difference for a given pipe length. This profile occurs when the total energy loss by friction is just balanced by the total energy gain due to uniform downslope. This paper presents a comprehensive analysis based on the energy-gradient ratio (EGR) approach to identify the optimal (or ideal) pressure profile (Type IIb), to achieve the minimal point of the relative maximum pressure variation, Φ H , which can be defined as the ratio of the maximum allowable pressure head difference (ΔH max ) to the total friction drop (h f(L) ). This minimal point is regarded as 'the most efficient pressure profile' or 'ideal hydraulic design' in the existing literature. For this purpose, an illustrative figure ( Figure 4) was developed to compare values of the relative maximum pressure variation versus the dimensionless EGR (K S = S 0 /S f ) for all types of pressure profiles. In this figure, the present ϕ H curve versus K S values allows the design engineer to make a decision for the best alternative for selecting the K S value, where for a given pipe slope (S 0 ) the K S value can be selected to meet the minimum pressure variation [K S =1, (ϕ H ) min =0.36] or the range of pressure variation as close to the minimum point as possible. The present design technique may provide a useful decision support tool for achieving a good design solution among hydraulically possible alternatives with minimal pressure head difference, and results in a higher level of water application uniformity along the multi-outlet pipeline system. RÉSUMÉDéterminer les profils réels de pression le long de tuyaux porte-rampes avec une pente uniforme est très important pour la conception hydraulique appropriée des systèmes de distribution d'eau. Dans la pratique, il existe trois profils de pression généraux (type I, type II et type III) le long des tuyaux en fonction de différentes situations de pente uniforme. Parmi tous les types de profils de pression, le profil type IIb est considéré comme le profil de pression optimale (ou idéal) qui peut produire la perte en charge minimale pour une longueur de tuyau donnée. Ce profil se produit lorsque la perte totale d'énergie par frottement est juste compensée par le gain d'énergie totale en raison de la pente descendante uniforme. Cet article présente une analyse complète sur la base du rapport de gradient d'énergie pour identifier la combinaison optimale (ou idéale) du profil de pression (type IIb) pour obtenir le minimum de variation relative de la pression maximale, ΦH. ΦH peut être défini comme le rapport de la différence de hauteur ...