STATIC ANALYSIS OF THE INLET SPHERICAL VALVE FROM A FRANCIS TURBINE

Abstract

Spherical valves are used for blocking the water flow in the penstock of high-pressure hydraulic turbines. The spherical valves close in the following cases: turbine load rejection, safety shutdowns, shutdowns for inspections and repairs. Valve components are subject to mechanical stress in both the "closed" and "open" positions. At valves used for a long period of time in an operating mode with multiple starts/stops, fatigue may occur. In this paper are analyzed the stress and displacement distributions for an inlet spherical valve from a high head Francis turbine. The stress distributions are analyzed at the main components of the valve: impeller, casing and trunnions. The identification of the variation of stress values between the stress state corresponding to the "open" and "closed" positions allows to determine the stress cycles.