Abstract: A fault-tolerant system relieves pressure of fluid flow in a drilling system. Redundant pressure relief valves can open to relieve fluid flow from a discharge outlet of a manifold when over pressurization is detected. A hydraulic arrangement operably connected to the redundant relief valves provides hydraulic motive force in redundant hydraulic circuits respectively to the redundant relief valves. The redundant circuits are cross-connected to one another. Pressure transducers distributed in the hydraulic arrangement measures operational pressures of the hydraulic arrangement. Redundant controllers can both control the hydraulic motive force provided in the redundant circuits respectively to the redundant relief valves to open and close the relief valves in response to the pressure level measurement.