The document provides information about various components in hydraulic brake systems, including: 1) A residual check valve keeps slight pressure in the system to prevent air leaks, while proportioning valves limit rear brake pressure to improve balance during hard stops. 2) A pressure-differential switch lights the brake warning light if pressure is lost in one circuit, while a brake fluid sensor does the same for low fluid level. 3) Common valves like metering valves and electronic proportioning systems work to properly time and balance brake pressure between the front and rear.