Design and Analysis of Double Wall Bellows for Valve Technology

Abstract

Tokamak is a fusion reactor used for fusion power generation research experiments. Gen- erations of plasma requires to maintain very high vacuum belows 10-7 bar in the chamber known as vacuum vessel. For this purpose a set of cryopump is used. This cryopump is working under varying loading conditions of the pressure and speed. Operation of cryopump requires to maintain speed of pumping. In order to maintain its speed a arrangement double wall bellows is used. The vacuum system of cryopump is needed the isolated environment during the pumping procedure. It is required to design a leak proof bellows arrangement. To maintain vacuum into the gas chamber of cryopump a disc valve is used for opening and closing of the chamber. As this operation is reciprocating in nature chances of disturbing vacuum in chamber are high. To prevent this leakage and to provide proper sealing, is complicated task which required proper design and analysis. The aim of the present work is to prevent leakage from actuator chamber (at room tem- perature and pressure) to application chamber(vacuum around 10-7 bar ). The double wall bellows assembly needs to be designed to sustain ultra high vacuum. For this application bellows has to under go higher compression and expansion same as cycling loading. And the double wall bellows assembly is necessary to maintain working conditions under prescribed parameter, which is highly useful for the purpose of the preventive maintenance. The design of the bellows assembly is carried out using Expansion Joint Manufacturing Associations (EJMA) standards. Here the results also demands for the valve shaft of the cryopump for bending criteria. As valve shaft is overhang in nature, which is supported by the main ange of the cryopump. Analysis of the bellows and valve shaft is done with standard FEA tool. And the results of which is are coming within satisfactory limits.