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2025
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Can air leaks also brake the car? Why use a four-circuit valve?
Recently, we saw a card friend in the community asking about the brake system, and the post mentioned the four-circuit valve. So what exactly does this four-circuit protection valve do? In fact, it is an important component of the air brake system, which can ensure the braking safety of the vehicle when the air circuit leaks.
● What is a four-loop protection valve?
First of all, we need to know that the braking system of trucks is usually divided into oil brakes and air brakes. Oil brake response speed is slightly slower, low strength, generally oil brake is mostly used in micro-surface, micro-truck and other models, characterized by small size, light weight and simple structure.
The air brake brake responds quickly and has strong braking power, which is mostly used in medium and heavy trucks, with large parts such as air storage tanks and brake sub-pumps, and now many light trucks have also changed from oil brakes to air brakes. The four-circuit protection valve exists in the air brake system and is used to divert and protect the air pressure pipeline of the whole vehicle.
The four-loop protection valve is essentially a five-way valve, and its internal structure is diaphragm, which is mainly composed of a shell, diaphragm, valve, transmission ring, push plate, pressure regulating spring, etc. There is one air intake, four air outlets. Among them, the air outlets 21 and 22 correspond to the front axle brake system and the middle and rear axle braking systems, and the air outlets 23 and 24 are connected to the parking brake system and the auxiliary braking system respectively.
● The function of the four-circuit protection valve
After dividing the brake system into four circuits that are both interconnected and independent of each other, it can ensure that when one circuit fails (broken or leaking), it will not affect the normal operation and inflation of other circuits, and at the same time, the air pressure of the failed circuit can be appropriately supplemented or even closed to play a protective role.
In other words, even if one air circuit fails and leaks, the four-loop protection valve can still retain about 6.5 brake air pressure in the remaining circuits and provide braking effect.
● Why do trucks use four-loop protection valves?
So why do trucks need to have a four-circuit protection valve? In fact, it is to ensure the reliability of the vehicle's braking system. Just imagine, if the brake system does not have a four-circuit protection valve, the air paths in all directions are directly connected. In case a pipeline is scratched by a small pebble bouncing off the road, it will cause the entire brake air path to completely lose air pressure, and the brake will have no effect, which will cause a major traffic accident.
Therefore, according to regulations, when a pipeline fails, it is necessary to ensure that the emergency braking can be effective to stop the vehicle. In order to meet the above requirements, the vehicle should use two or three independent storage energy circuits, not only to separate the energy storage circuits, but also to separate the operation circuits at the same time, independent of each other, to ensure that the air compressor can continue to inflate to other undamaged pipelines.
● Common fault problems:
1. A circuit is not inflated or leaking
Fault phenomenon: weak brakes, or even failure
Cause of failure: There is moisture in the airway, which will cause extensive corrosion of the lumen and block the air valve after too long. Corrosive foreign matter falls off, affecting the rupture of the diaphragm and causing air leakage. At this time, it is necessary to disassemble and inspect the four-circuit valve, and check the safety valve and check valve. If the valve is stuck, it can be cleaned and reassembled, and if the valve is damaged, it needs to be repaired or replaced.
At the same time, it is also necessary to check whether the drying tank is damp or leakage, whether the service life has expired, and replace it in time.
2. Air pressure imbalance
Fault phenomena: slow pumping, fast air use, air brake cannot be released, clutch pedal is heavy
Fault cause: Because the four-circuit protection valve has adjusted the opening air pressure of each branch before leaving the factory, the malfunction is likely to be caused by damage and deformation of the diaphragm, valve seat and piston assembly, or improper adjustment after maintenance and replacement of relevant accessories, resulting in pressure limitation.
● Postscript:
To put it simply, the four-circuit protection valve can ensure the normal operation of each air circuit in the brake system and play the role of hub diversion and control. Of course, if this part fails, there will be phenomena such as the handbrake not being released, the clutch pedal is heavy, and the air horn is not ringing.
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