Forensic Analysis of a Large-Diameter Knife Gate Valve Performance

Knife gate valves (KGVs) are frequently used in pipeline systems as on-off valves and to enable isolation and servicing of other system components. This type of valve operates by lowering a steel plate between two seal rings that are integral to the valve body. This paper presents an evaluation of performance problems with 2,130 mm (84 in) diameter KGVs, including seal-ring clearance and opening tolerance issues. Loads that act on the knife gate valve include selfweight, internal water pressure, tension from the bolts connecting the valve to the adjacent pipe, and gasket compression loads. We present the results of extensive non-linear finite element analysis, including contact between the pipe flanges, rubber gaskets, and the valve body. The model was used to evaluate valve deformation and determine the root cause of the observed performance issues. A favorable comparison of the model results and measured deformations is presented. We show how modeling was used to guide the design of a modification which resulted in satisfactory valve performance and provide some recommendations about design of valves of this type.

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