The double-chamber brake chamber has both an inflatable brake chamber and a deflated brake chamber. Force is generated by inflation and deflation for wheel braking. The air-filled brake chamber is used for service braking, and the deflated spring brake chamber is used for parking and emergency braking. The main feature of the spring brake chamber is to obtain a mechanical braking force by releasing the spring energy.
Generally speaking, the meaning of service brake is the foot brake we usually talk about, which is the braking force generated by stepping on the brake. (Usually we can see that when there is a trailer driving on the road, the deflated sound heard by the brakes is the spring brake air chamber.)