Improvements in or relating to valves for fluids

This relates to valves for fluids with particular application where the fluids are toxic, radioactive or valuable so that leakage into the environment must be reliably prevented or where contact with surrounding atmospheres or fluids must be prevented. The particular application considered is for process gas valves in the pipework in centrifuge cascades for the separation of the 235U and 238U isotopes of uranium where the process gas is uranium hexafluoride. Additional safeguards are provided as a precaution against bellows failure on bellows-sealed valves. It includes a bellows mounting member to which one end of the valve bellows is sealed, the other end being sealed to the valve closure member. This is interposed with the provision of sealing means, between two separate portions of the valve body. There is a valve operating member secured to the valve closure member and in a bore in one end of the valve body parts with a seal between. There is a rotatable member held against the longitudinal movement in screwthread engagement with the valve operating member; this is rotated to operate between valve open and valve closed positions. Valved communication to an interspace between the bellows and the appropriate seal allows testing during operation for inleakage and outleakage. (U.K.)