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What's the purpose of a dump truck dryer? How do you adjust the air pressure?
The so-called 'mud truck' refers to large heavy-duty dump trucks that transport sand, soil and other construction materials on building sites, often with their cabs covered in mud. That's why they're jokingly called 'mud trucks'. These types of vehicles usually use air brakes, with main components including an air pump, dryer, air pressure regulator, four-way valve, air reservoir, foot brake valve, hand brake valve, relay valve, quick release valve and brake wheel cylinder.
▎ What are the functions of a dryer and a pressure regulator?
In a pneumatic braking system, compressed air is the working medium. It needs to maintain a sufficiently high and stable pressure and be clean enough to ensure the normal operation of all the system's valves. To achieve this, the system is equipped with a dryer and a pressure regulator. Their role is to provide the braking system with clean and dry compressed air and keep the system pressure within a normal range (usually 8~10 bar). To simplify the system, these two components are usually combined and called a dryer assembly. I won't go into the working principle, or you'll fall asleep.
How to adjust the brake system air pressure
On this assembly, there is a pressure regulator valve that can adjust the system pressure. When the system pressure reaches the set level, the pressure regulator valve opens, releasing the compressed air from the air pump through the regulator's exhaust port, and the system pressure stops rising, allowing the air pump to run without load.
If the system pressure releases before reaching the set level, we can turn the adjustment screw of the pressure regulator valve clockwise, and the system's exhaust pressure will increase.
If the system pressure reaches or exceeds the specified pressure and the relief vent hasn't operated, we can turn the adjustment screw on the pressure regulator anticlockwise to lower the system's venting pressure. We repeat adjusting this screw until the venting pressure reaches the system's specified pressure. However, in practice, this pressure regulator is unlikely to be damaged, and its adjustment pressure generally doesn't change. If the brake system pressure suddenly fails to rise, it is usually due to a leak or other system fault.
If compressed air is escaping from the exhaust port of the pressure regulator, it means the internal rubber seal is damaged. Usually, this happens because the air pump is leaking oil or the drying tank has lost its drying function. At this point, we should replace the dryer assembly and repair the air pump, rather than just adjusting the exhaust pressure of the regulator.
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