The semi-trailer is equipped with a pneumatic brake device that acts on all wheels. When the car is driving, use the foot brake. When parking, use the parking hand brake. At the same time, a dual-line pneumatic brake system is used. The semi-trailer is equipped with an emergency relay valve and a trailer air tank, etc. The right one is a brake line, which is connected to the wet air tank of the tractor through a connecting valve. Regardless of whether the semi-trailer is braking or not, it always charges the trailer air tank; the left one is a control line, which is connected to the tractor's double-chamber brake valve through a connecting valve. The control line is usually airless. When braking, the tractor's double-chamber brake valve uses the compressed air in the front circuit air tank as a signal to control the trailer's emergency relay valve, and the emergency relay valve sends the compressed air in the trailer air tank to the trailer's brake air chamber.
The semi-trailer's braking system is equipped with a dual-line pneumatic brake. When the semi-trailer is continuously braking down a long slope, it can always charge the trailer air tank. When the semi-trailer and tractor are accidentally uncoupled or the trailer's air pipe leaks, that is, the air pressure is lower than the specified pressure, the trailer can automatically perform emergency braking, and the main vehicle's rear brake circuit does not lose its braking effect. Due to the high sensitivity of the emergency relay valve, it is placed as close to the trailer's air tank and trailer axle as possible in the pipeline layout, and a thicker air supply pipe is used.
