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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 referred to as the dryer assembly. I won't go into how it works, or you'll fall asleep.
▎How to adjust the brake system air pressure
On this assembly, there is a pressure regulating valve that can adjust the system pressure. When the system pressure reaches the specified level, the valve opens, venting the compressed air from the pump through the exhaust of the pressure regulator, so the system pressure stops rising and the pump runs without load.If the system doesn't reach the specified pressure before venting, we can turn the adjusting screw of the valve clockwise to increase the exhaust pressure of the system.
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 has leaked 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 pressure valve.
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