Does a Four-Circuit Damage Affect Braking?
3 Answers
Four-circuit damage affects braking. If a certain pipeline in the four-circuit system is blocked or leaking, the air pressure gauge will show abnormal pressure. When the four-circuit system is damaged, it can affect the normal operation and inflation of other circuits. Four-circuit faults: If there is a leak in one of the four circuits or the four-circuit protection valve has been in use for too long, the built-in spring may rust and become stuck. If one needle on the pressure gauge reaches 6 units of pressure while the other shows no pressure at all, it indicates a leak in one of the four circuits. Due to the leak, the four-circuit protection valve automatically closes, causing the air pressure gauge to fail to build pressure and resulting in insufficient air supply. Similarly, if the four-circuit protection valve has been in use for too long and the built-in spring rusts and becomes stuck, the air pressure gauge will also fail to build pressure, leading to insufficient air supply. Both of these issues can be addressed by replacing or repairing the components at an auto repair shop. Function of the four-circuit protection valve: The main role of the four-circuit protection valve is to distribute the dried air into four circuits to meet the needs of different vehicle systems (such as the service brake system, parking brake system, air suspension system, and door control system). It also ensures that if one circuit fails, the other circuits can still operate normally and provide appropriate compensation for the failed circuit's air pressure.
After driving for so many years, especially in the field of heavy-duty trucks, I have personally experienced the role of the four-circuit protection valve. It is responsible for distributing compressed air to four independent circuits: the front wheels, rear wheels, trailer, and auxiliary systems. If this valve is damaged, the air distribution becomes uneven, leading to brake failure in certain circuits. For example, if the front wheel circuit malfunctions, control can be lost during emergency braking, while a rear wheel circuit failure can increase braking distance. This is particularly dangerous on long downhill sections because the system cannot provide stable pressure. I recommend fellow drivers to regularly check the air pressure gauge and the valve for leaks. Identifying issues early can prevent major repairs, and routine maintenance should include cleaning the valve to prevent clogging from dirt. If you feel the brakes are spongy while driving, pull over immediately for inspection—don't push through. Safety comes first.
Having worked in the maintenance station for years, I fully understand the pivotal role of the four-circuit protection valve in the air brake system. It coordinates the air pressure distribution across four circuits. Once the valve is damaged due to rust or aging seals, it can impair braking performance. Common failures include uneven circuit pressure, which may cause sudden loss of braking on the front or rear wheels, or sluggish response when pressing the brake pedal. For diagnosis, first check if the air pressure at each port is consistent, and use an oscilloscope to detect leakage points. Regular maintenance involves cleaning the valve passages and replacing the filter elements every 20,000 kilometers. If you notice abnormal brake pedal resistance, don’t hesitate—visit a professional repair shop promptly to prevent minor issues from escalating into accidents.
