Pressure Transients Caused by Air-Valve Closure while Filling Pipelines

Abstract

Air valves are normally installed at high points along undulating pipelines to allow for air discharge or intake during filling or dewatering. Initial filling of a newly constructed pipeline, or refilling a portion of an existing pipeline after a shut-down for maintenance purposes, can produce destructive pressure surges caused by air-valve closure. Methodologies for determining safe filling rates for the pipeline, taking into account factors such as air-valve characteristics, riser dimensions, driving head, and allowable working pressure, are proposed in this paper. An optimal filling method can be achieved either by a two-stage filling procedure, which comprises a fast filling rate during the first stage and a slower filling rate during the second stage when the water level approaches the highest air valve, or by using an antislam air valve. The comparison of computed transient pressures with test data indicates that the analytical models produce reasonable predictions of pressure surges caused by air-valve closure.