Actually it just interrupts the boost signal from the intake manifold to the ALDA if it exceeds a set pressure. The line from the intake manifold should run through it before the ALDA

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine