Chapter11 Valves 12

Valves 11.1 CHAPTER 11 Valves Introduction The conduits in all water power plants except large low head plants, are ordinarily rn1e orov2.7(d)-deadl ead shut off devices. Generally these components are valves. They exist in different types and design depending on function and requirements. In any power plant valves for different purposes are usually needed. Normally it is a shut-off valve just in front of the turbine. In this way the turbine may be emptied without emptying the shaft or penstock. In addition the guide vane cascade is depresserised so that leakage flow is avoided. With a long head race tunnel and surge chamber it is normal to have a shut off valve just downstream of the surge chamber. In this way the shaft or penstock may be emptied without emptying the tunnel. To prevent large damage at an eventual rupture of the penstock, a pipe break valve is normally installed in the pipe just downstream of the shut off valve. This valve closes automatically when the water velocity exceeds a certain set value. The most relevant types of valves are: - spherical valves - butterfly valves - gate valves - ring valves 11.1 Spherical valves Spherical valves are applied mostly as shut off valves in front of high head water turbines. They are however, used as pipe brake valves as well. Spherical valves are presently covering a pressure range of 160 m to 1250 m water head. The spherical valves consist of the valve housing with flanges, valve rotor, bearings and seals. 11.1.1 Valve housing and valve rotor The valve housing has a spherical shape. It may either be axially split permanently in two halves and bolted together with heavy flanges, or these two halves may be welded together after the rotor has been installed.

Chapter11 Valves 12

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