Booster This booster is the hydraulic operation 1. Unloading Valve booster. Depress the brake pedal, the oil 2. Slid Valve comes from steering pump applies into 3. Boot booster piston (6) and the hydraulic force 4. Master Piston in the piston (7) will increase. 5. Shell 6. Booster Piston 7. Piston 8. Slid Valve 20-81