Abstract
The aim of this paper is to show how surge diagrams follow logically from two simple principles: The propagation of pressure waves at the speed of sound, and Joukowsky's law expressing the relation between variations in pressure head and in velocity head.
Surge lines are a manner of plotting Joukowsky's law and of showing how energy which is being introduced into a pipe or is being drained from it can be converted from one form into another.
Complications can be avoided in drawing surge diagrams by recognizing the truly significant factors. If this is done, most practical problems can be studied with adequate accuracy by simple diagrams.
The methods used are illustrated by typical examples from the frequent problem of a power failure in a pumping station. Excessive surge pressures are usually avoided by providing an air vessel or a flywheel, the aim being to stop the column of water gradually and to dampen out the oscillations. Special care is needed in avoiding the formation of voids or air spaces anywhere in the system.
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