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Residual ValveTwo types of residual valves are common in today's properly engineered brake systems. A 10-pound valve is used to maintain line pressure, in order to keep the rear brake shoes closer to the surface of the drums, which in turn, gives a higher, firmer pedal. A 2-pound residual valve is needed for applications where the master cylinder is mounted lower than the calipers (like many street rods). It performs an important job by preventing backflow (of fluid) from the calipers to the master cylinder.