ABSTRACT
A knowledge of the hydraulic gradient is of value since it indicates the pressure variation to which the pipeline is subjected. The maximum pressure head governs the stress which the pipeline must be designed to withstand. Apart from the important requirements of service connec tions, the minimum pressure head may not have any great significance. This arises from the fact that, provided the hydraulic grade line is always above the pipe section, the pressure will not fall below atmo spheric. Even if over a certain length the hydraulic grade line does lie below the pipe section, discharge will be maintained by siphonage up to about 7-5 m negative head, at which point vaporisation may be expected to commence. It is good design practice, however, to site the pipeline so that the pressure does not fall below atmospheric. This is to avoid any risk of impurities being sucked into the pipeline.
