Fuel Pressure Safety Switch only (Low Pressure) Nitrous Outlet DJP Performance Performance Parts Nitrous Express Switch Panel Nitrous Express EFI Fuel Pressure Safety Switch w 4AN Manifold Nitrous Fuel Solenoid (25psi) with V Purge and 4AN Adapter Drag Race Amazon.com: Nitrous Outlet Fuel Pressure Safety Switch & 4an manifold. This safety switch automatically shuts off the nitrous flow if fuel pressure drops below the user adjustable set point. Includes a billet Aluminum 4an manifold that allows you to install the fuel pressure safety switch in line with a 4an fuel fitting.