When braking, step on the brake pedal, the pedal force is enlarged by lever to operate on the control valve putter. First, the control valve push back spring is compressed, and the control valve putter moves forward along with the air valve column. The vacuum one-way valve is closed when the control valve is moved forward to the position of the control valve leather bowl in contact with the vacuum one-way valve seat. At this time, the booster's true air chamber, the application gas chamber is separated. At this point, the air valve column ends in contact with the surface of the reaction disk. The air valve opening will be opened as the control valve pusher continues forward. After the outside air is filtered through the open air valve and access to the air chamber, the air chamber (right air chamber) is entered into the booster and the servo force is generated. Because the material of the reaction disk (rubber piece) has the physical property requirement of the unit pressure in all places of the force surface,The servo force increases with the gradual increase of the input force of the control valve. Servo force due to the limited resources, when the maximum servo power, namely the application of air chamber of the vacuum is zero (that is, a standard atmospheric pressure), servo power will become a constant, no longer change. At this point, the input force and output force of the booster will increase by the same amount. Cancel the brake, with the decrease of the input power, control valves putter move backward, the vacuum one-way valve port open, booster true air chamber, the application of air chamber are interlinked, servo power decreases, and the piston body backwards. As the input force decreases, the servo force will be reduced to a fixed ratio (servo ratio) until the brake is completely removed.