High security valve for pipelines carrying noxious gases - has two valve plates closed by pressurising casing and opened by evacuating

摘要

The valve is a conventional double-seat valve, in which two plates (6,7) can be pressed against seatings with surrounding seals (12,13) thus closing the opening into the two pipes (3,4) entering the valve casing (2). A pressurising system (11) ensures that a specific pressure is produced inside the valve casing between the two valve plates (6,7); to close the valve, this specific pressure is equal to or greater than the highest pressure in either of the two adjacent pipes (3,4), while to open the valve it is equal to or lower than the lesser of these two pressures. Preferably, when the higher pressure is applied to close the valve, a gas is used which is non-ktoxic but is compatible with the process gas in the pipeline.