What is the method to check if a relay valve is broken?

[DamianLee]

The method to check if a relay valve is broken is as follows: A damaged relay valve can cause slow brake return, and in severe cases, even lead to brake lock-up. The function of the relay valve: It prevents simultaneous operation of the driving and parking systems, overlapping forces in the combined spring brake cylinder and spring brake chamber, thereby avoiding overload on mechanical transmission components and enabling rapid air charging and discharging in the spring brake cylinder. When the brake pedal is pressed, the output air pressure from the brake valve serves as the control pressure input for the relay valve. Under this control pressure, the intake valve is pushed open, allowing compressed air to flow directly from the air reservoir into the brake chamber through the intake port, bypassing the brake valve. This shortens the air charging pipeline of the brake chamber and accelerates the air charging process.

[DiJudah]

I remember last time when driving a heavy truck, the brakes felt sluggish. I tried checking for a faulty relay valve myself: first, park the truck stably and turn off the engine, then restart and lightly press the brake pedal, carefully listening for any hissing air leaks near the valve position—this is the most direct method. Also, check the brake air pressure gauge; if the pressure doesn't rise or fluctuates severely, it could indicate a stuck or leaking valve. During an actual driving test, if you feel uneven braking between the left and right wheels or a dragging sensation, it can also confirm the issue. I also inspected the pipe connections for looseness or oil leaks, ensuring no dust was clogging them. Safety is the top priority; neglecting such issues can lead to brake failure and increase the risk of accidents, so even minor problems should be sent to the shop immediately. Developing a habit of regularly checking air pressure and cleaning can prevent wear, save fuel, and provide peace of mind.

[OJohnny]

To check if the relay valve is faulty, focus on these key points as I do: Use simple tools like a pressure gauge connected to the outlet to measure if the pressure responds quickly when braking—delays or failure to meet standards indicate a fault. Visually inspect the valve body and surrounding pipes for cracks or signs of leakage. Listen for abnormal sounds like air leaks, which help diagnose internal component damage such as springs or diaphragms. Common causes include moisture corrosion or debris blockage. I remind friends to regularly maintain the air system, including replacing the air dryer. If these symptoms are found, replace the part promptly to avoid compromising overall braking safety. These techniques are suitable for daily maintenance and efficiently pinpoint issues.

[JordanLynn]

If there is abnormal noise or unsmooth braking while driving, it may indicate a faulty relay valve. When I inspect it myself, I first check if the car is in a parked state and listen for air leakage near the valve while pressing the brake pedal. Then, I look for loose or leaking connections. I also test for delayed brake response during low-speed driving. A little trick I learned online is that rust on the valve can cause it to stick, leading to brake shudder—cleaning it usually helps, but I rarely do it myself to avoid mistakes. Safety comes first, so if any issues are found, I immediately take it to a professional shop to prevent delays. This component affects driving stability, and I always learn something new to handle similar faults.