Proflow Pressure Relief Valve, Supercharger, Universal, -04AN ORB, Black - PFE621-04BKPart Number: PFE621 04BK This manual pressure relief valve can be used to relieve pressure in superchargers by pressing down on the plunger. With either AN4 or 1 8 NPT thread, they can be used for many other applications also where pressure relief is sometimes necessary. Comes in a black anodised finish. Tested to withstand up to 40 PSI.