1307479 Brakes DR ING hcF PORSCHE KG 20 Sept 1971 [18 Sept 1970] 43829/71 Headings F2E and F2F In a two-circuit brake installation, each brakelining carrier is actuated by two cylinders 1, 2 which are normally separately operated by tandem cylinders 6, 7 via lines 3, 4. These lines are normally fed from lines 11, 12 through grooves 36, 37 in spring loaded control pistons 16, 17. These pistons normally receive pressure at each end from each supply so that they remain balanced and do not move. At the same time differential pistons 14, 15, each of two diameters, are likewise balanced by pressure at the ends matched by pressure at the middle. When one system fails so that its pressure - collapses, the differential piston still having pressure at its large outer end, moves to the left because there is no counterbalance pressure at its middle from the other circuit. This concentrates the pressure at the end of smaller diameter and feeds an extra pressure to the remaining active brake cylinder, 1 or 2. The extra pressure fed to the left-hand end of piston 14 or 15, together with the failure of pressure at its other end from the other circuit, causes it to move to the right. This closes off the grooves 36, 37 to prevent leakage back of the pressurized fluid now acting in the surviving circuit. At the same time it closes a switch to energize warning light 44 or 45 as the case may be. As shown the rear wheels also have a two-circuit energization, but they may have only a single circuit (Fig. 1, not shown). The control pistons may be moved by electromagnets 46 energized from pressure detectors 47.