Unexpected wear and failure of swing check valves cost power plants and water treatment facilities millions of dollars each year. Operating swing check valves at too low flow velocities can cause the check valve internals to rapidly wear and suddenly fail. Many of the swing check valve failures could have been avoided by the use of a minimum velocity limit or a numerical model to predict the limit of minimum velocity. The following equations and methodology can be used to predict a minimum velocity limit or VMIN for swing check valves. The limit of VMIN is defined as the minimum flow velocity in which the valve disk is fully open and stable without motion. The procedures and equations can also be used to predict the velocity (VOPEN) to just open the disk to any position or angle. The equations presented in this paper are also unique in that they can be applied to swing check valves that have large degrees of disk position or valve opening. The equations are not limited to swing check valves that must have a portion of the valve disk protruding into the flow through the check valve. Although the methodology was developed primarily for horizontal liquid flows, limited testing has shown that the equations can be applied for installations with inclined slopes and for applications with compressible fluids. The following equations were derived from a large data base of tests of different sizes and types of swing check valves. Tables and figures are presented to support the suggested equations.

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