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2026
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Smart use of the adapter valve easily solves the trailer's empty brake locking problem
Have you ever encountered this problem—when the trailer is empty, pressing the brakes causes the wheels to lock, leaving tire marks and smoke? If so, you definitely shouldn't miss this article.
Friends, in the face of declining environmental benefits in transportation, we should change old and bad driving habits. With the experts in the forum generously sharing their knowledge, truck drivers should seriously learn and understand the latest technology and knowledge, apply it reasonably, reduce our operating costs, and embark on the road to wealth!
Getting back on topic, quite a few truck enthusiasts have encountered problems similar to mine. Since the trailer brakes have to engage before the tractor, but most trailer brake pads nowadays are rated for 16 tons and the vehicles are lightweight, when braking with an empty trailer, the tires leave skid marks and smoke. This issue leads to two consequences: in mild cases, abnormal premature tire wear; in severe cases, during rain or snow, it easily causes fishtailing and skidding, resulting in unnecessary damage.
Because of this problem, well-known forum members, including 'Haste Makes Waste' and Engineer Jiang from WABCO (I'd like to take this opportunity to thank both of them for their hard work), have discussed it extensively. Engineer Jiang's solution is this — an adapter valve.
Working Principle of the Adaptor Valve
This is an adaptor valve used for the front wheels of a Howo truck. According to Brother Jiang, my understanding of its principle is that if the input air pressure is 3 kg, the output is 1 kg; if the pressure exceeds 3 kg, it passes straight through without attenuation! This prevents the front wheel disc brakes from working too harshly.
The part circled in red is the intake side, and the blue part is the outlet side. This valve has one intake port and three outlet ports! Only two are visible along the way; the other is on the back.
The adapter valve is connected in series with the main vehicle-trailer valve and the trailer relay valve control air circuit! My installation position is at the gooseneck of the trailer. Locate and disconnect the control air circuit of the relay valve; the red-circled position is the air inlet, and the white one is the air outlet (the adapter valve has three outlets, block two and use one). With this setup, lightly pressing the brake will make the trailer respond smoothly, and pressing hard will not affect the braking force!
A friend asked how to install it? Usually, in the trailer's longitudinal beam, there are two pipes, red and yellow. These two lines are connected from the tractor to the trailer through a spiral hose. One line is for inflating the trailer's air tank, and the other is the control air line from the tractor-trailer valve to the trailer relay valve, which is yellow! (Color may vary depending on the vehicle.) Disconnect the yellow line (at an appropriate location to install the adapter valve), connect the end coming from the tractor to the adapter valve's air inlet (solid black line), and connect the other end to the adapter valve's air outlet!
This way, gently pressing the brake makes the trailer respond smoothly, and pressing hard doesn’t affect braking force! Fellow drivers, I just installed it today, and it’s amazing!
Focus on the research and development of automotive brake systems and pneumatic brake valves to promote the development of the auto parts industry!
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