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2026
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Pay attention to potential air leakage in the auxiliary air tank
In the air system of a truck, leaks in the auxiliary air tank are often overlooked, which frequently leads to the problem where the air pressure gauge shows normal readings, but the clutch booster pump cannot work properly. After the vehicle has been parked for a while, frequent pumping of air is required. This phenomenon occurs because the air pressure gauge or the low air pressure warning sensor, usually installed on the front and rear brake air tanks respectively, cannot easily detect leaks in the auxiliary air tank from the instrument readings.
Generally, vehicles equipped with a four-circuit air protection valve typically have 3-4 air reservoirs, each supplying air separately. The air supply sequence also follows a certain order: rear axle brake air reservoir → front axle and control circuit air reservoir → auxiliary equipment air reservoir → parking brake air reservoir. This design ensures that the braking system stores air first. The clutch booster pump only starts to work normally when the pressure gauge shows air pressure above 6 bar, and the parking brake (air release brake) is only released last.
● Components connected to the auxiliary air reservoir
The function of the auxiliary air reservoir is to provide air for auxiliary equipment that requires it. The commonly connected components are:
① Clutch booster pump
② Exhaust brake butterfly valve
③ Transmission shift cylinder and differential lock (for heavy trucks)
④ Air horn
● Leaks in the auxiliary air reservoir can lead to the following faults:
① If the auxiliary air reservoir pressure is insufficient, the most direct fault is that the clutch booster pump cannot work properly, preventing the clutch from disengaging. After a long period of parking, starting the engine will consume a large amount of fuel to restore air pressure.
② The transmission shift cylinder cannot operate properly, which can lead to serious transmission faults.
③ The exhaust butterfly valve or air horn does not work.
● Causes of leaks in the auxiliary air reservoir:
① Components prone to frequent leaks, with the air horn being the most common. Its pipelines are relatively thin and long; especially in dump trucks, long-term heavy vibrations make leaks very likely to occur.
② Various pneumatically controlled solenoid valves. Leaks in these components are usually not severe and require careful inspection.
● Fixing leaks – modifications should be done cautiously:
Based on practical experience with dump trucks, some connect the air circuits of the clutch booster pump and shift cylinder to the rear brake air reservoir. This avoids interference caused by leaks in other auxiliary equipment pipelines, but this carries safety risks. The correct solution to leaks is to thoroughly inspect the cause and replace with qualified components. Modifications should be done cautiously with safety and reliability as the premise, and one should not risk major issues for minor fixes.
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