An advanced, validated analytical model for predicting total required thrust to operate unbalanced disc globe valves (Fig. 1) has been developed that overcomes the limitations of the previous industry models and accurately predicts opening and closing thrust requirements throughout the valve stroke under a variety of design basis conditions. The previous industry models predict required thrust only at the fully closed and fully open positions; and do not address mid-stroke thrust requirements or potential for mid-stroke damage that can occur especially under high flow conditions. These limitations were overcome by developing a first principles based model, which predicts fluid forces and moment on the disc, disc-to body reactions, and disc-to-body friction forces throughout the stroke. The analytical model relies on force and moment coefficients that were derived from CFD (Computational Fluid Dynamics) to predict fluid forces and moments on the disc. The analytical model also identifies potential for “unpredictable behavior” resulting from disc/body reaction forces exceeding threshold of material damage. Finite Element Analyses (FEA), including elastic-plastic modeling of localized regions, were performed to predict internal forces, reactions and potential for material damage.

The model has been validated against a variety of disc and body geometries and fluid conditions, including water flow loop test sponsored by Electric Power Research Institute (EPRI), as well as recent steam testing under blow-down conditions performed by Kalsi Engineering, Inc. (KEI) for a variety of disc and body geometries and fluid conditions. The model overcomes the applicability limitations of Electric Power Research Institute (EPRI) MOV Performance Prediction Program (EPRI PPP) as well as Joint Owners’ Group (JOG) MOV Periodic Verification Program, and it can be used to reliably predict thrust requirements for globe valves under design basis conditions.

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