Correct answer
Prevent excessive pressure in the circuit.
It prevents excessive pressure by limiting the maximum pressure of stored air. It is neither a hydraulic-circuit bleed valve nor the valve admitting air to the semi-trailer. Do not confuse it with a quick-release valve, which exhausts air from the brake chambers when braking stops, or with reservoir drain valves that remove water. Do not empty or tamper with the circuit to drive; follow the manufacturer’s maintenance instructions.
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Automatically bleed the air present in the hydraulic-fluid pipes.
Prevent excessive pressure in the circuit.
Allow air to pass to the semi-trailer.
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