Can the four-circuit protection valve adjust the clutch air pressure?
2 Answers
Four-circuit protection valve can adjust the clutch air pressure. Normally, the clutch of a heavy-duty truck should not be lower than 6 atmospheres, otherwise, issues such as a heavy clutch pedal and difficulty in shifting gears may occur. Function of the four-circuit protection valve: The main function of the four-circuit protection valve is to divide 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), while ensuring that when one circuit fails, the other circuits can still operate normally and appropriately compensate for the air pressure of the failed circuit. Common faults of the four-circuit protection valve: If one of the four circuits is blocked or leaking, the air pressure gauge will show an imbalance in air pressure. If a circuit is blocked or leaking, check whether the four-circuit protection valve or the one-way valve is stuck, or whether the diaphragm is broken, causing air leakage. The main cause of these faults is the presence of a large amount of moisture in the air passage, which leads to severe rusting inside the cavity, jamming the air valve, and the falling off of rusted debris causing diaphragm rupture and air leakage. The imbalance in air pressure can cause damage to the internal diaphragm, valve seat, and piston assembly during vehicle operation.
I worked in an auto repair shop for over ten years and have seen plenty of four-circuit systems on trucks, which manage several air pressure circuits, including the clutch supply. As for whether the clutch air pressure can be adjusted, it depends on the specific vehicle model. Many systems have dedicated adjustment nuts on the circuit valves—turning them can change the air pressure. When the clutch is too heavy to press, increasing the pressure can indeed make it lighter, but setting it too high will cause the clutch plates to wear out faster. It's best to first measure with a pressure gauge; the standard range of 6-8 kg is ideal. By the way, don’t overlook checking for air leaks in the pipelines—adjusting the pressure without fixing leaks will reduce effectiveness. If you're doing it yourself, bring protective gear—safety first. If you’re unsure, it’s more reliable to seek a professional shop to avoid damaging the system and compromising driving safety, especially for long-distance trips where caution is key.
