（1） Working status
When braking, the brake pedal is depressed, and the pedal force acts on the control valve push rod after being amplified by the lever. First, the return spring of the control valve push rod is compressed, and the control valve push rod and the air valve column move forward. When the control valve push rod moves forward to the position where the control valve cup contacts the vacuum valve seat, the vacuum valve port is closed. At this time, the vacuum and application air chamber of the booster are separated, and the end of the air valve column is just in contact with the surface of the reaction disk. As the control valve push rod continues to move forward, the air valve port will open. After air filtration, the outside air enters the application air chamber (right air chamber) of the booster through the open air valve port and the channel to the application air chamber, and the servo force is generated.
Because the material (rubber part) of the reaction disk has the physical property requirement that the unit pressure at all parts of the stressed surface is equal, the servo force increases in a fixed proportion (servo force ratio) with the gradual increase of the input force of the control valve push rod. Due to the limited servo force resources, when the maximum servo force is reached, that is, when the vacuum of the application air chamber is zero (that is, a standard atmospheric pressure), the servo force will become a constant and will not change.
At this time, the input force and output force of the booster will increase by the same amount; When the brake is cancelled, the control valve push rod moves backward as the input force decreases. When the maximum boost point is reached, after the vacuum valve port is opened, the vacuum of the booster and the application air chamber are connected. The vacuum of the application air chamber will decrease, the servo force will decrease, and the piston body will move backward. In this way, as the input force gradually decreases, the servo force will also decrease in a fixed proportion (servo force ratio) until the brake is completely released.
（2） Non working state
In the non operating state, the return spring of the control valve push rod pushes the control valve push rod to the locking position of the right lock plate, and the vacuum valve port is in the open state. The control valve spring makes the control valve cup and the air valve seat closely contact, thus closing the air valve port.
At this time, the vacuum air chamber and the application air chamber of the booster are respectively communicated with the application air chamber channel through the control valve chamber through the vacuum air chamber channel of the piston body, and are isolated from the outside atmosphere. After the engine is started, the vacuum at the intake manifold of the engine (negative pressure of the engine) will rise to -0.0667 MPa (that is, the air pressure value is 0.0333 MPa, and the air pressure difference from the atmospheric pressure is 0.0667 MPa). Subsequently, the vacuum of the booster and the vacuum of the application air chamber rose to -0.0667 MPa, and they were ready to work at any time.