Sealing technology manual for the process industry - Butterfly valve seals

BUTTERFLY VALVE SEALS Seals for butterfly valves ensure the reliable function of but- terfly and disc valves. In the food and beverage industry, they are used wherever a shut-off valve is sufficient and a more extensive flow regulation is not necessary. Shut-off butterflies, butterfly or disc valves are normally four- part units composed of a two-part housing with a threaded connector, weld-on ends or a clamp connector; a valve disc and a butterfly valve seal. It is only the last component that guar- antees the integrity of the entire unit, making it indispensable in preventing all three types of potential leakage – at the pipe seal, the flange and the actuator. Despite the simplicity of their basic design, seals for butterfly valvesareexpectedtomasterextremelydemandingoperating conditions:whenthevalveisopen,thegasketshouldonlymin- imally reduce the pipe diameter, and must be nearly free of dead space. The valve should be easy to close, but at the same time exhibit high compression when closed to provide a per- fect seal. Optimum materials, torque-reducing geometries, and highly realistic testing are needed in order to combine all of the desired qualities. The requirements are further intensified by the high flow speed when the valve is closing. This flow creates a major pres- sure differential and pressure fluctuations, both of which can blow the seal out of its seat into the pipe. In order to optimally tailor the seal design to prevent this, Freudenberg utilizes effi- cient and highly-effective computational models such as FEM. Dimensions • Dimensions fit standard DIN and ISO pipe dimensions • Standard metric: DN 15 to DN 250 • Standard inch: 1” to 6” • Individual dimensions available on request Types • Customer-specific types available on request thanks to FEM calculations • Special models with additional treatment (e.g. RFN) Installation and assembly • When stretching the gasket over the valve, avoid ledges, sharp edges and threaded surfaces on the shafts • Please refer to page 94 for general installation and assembly instructions 1 Optimal compression on the butterfly valve (or “valve disc”) ensures that the sealing location is reliably sealed. Here the goal is an ideal compromise between the integrity of the closed valve and the torque involved in actuating it 2 The quasi-static sealing location is also worth examining. If the compression is oriented correctly, the leakage of production and cleaning media is reliably prevented 3 The axle lead-through represents a particularly difficult sealing location. The optimal design dependably prevents leaks 3 1 2 1 3 2 Product portfolio 84

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