dear all
I have a question regarding isolation philosophy in following scenario: a compression stage have a common scrubber and 2 compressor and cooler in duty standby configuration.outlet of each compressor equipped with shut down valve which with a manual isolation valve provide double block isolation scheme.inlet line of scrubber will be depressurized and isolated by single valve which provided enough isolation. there are an spill back stream equipped with control and by pass valve. the stream is branched off from compressor discharge line after shutdown valve described before.for human entry to scrubber need a positive isolation against live plant.the problem in this regard is spill back stream. by pass stream of control valve has only a globe valve. which combination will provide proved isolation to insert spectacle blind on inlet stream of scrubber against leakage through spill back line and control valve bypas.