What is the function of a multiple-circuit safety valve in an air brake system?

In a multiple-circuit air brake system, the safety valve ensures that if one circuit develops a leak or fails, it is sealed off from the other circuits. This prevents the entire brake system from losing air pressure. At the same time, the valve guarantees that the remaining intact circuits continue to receive compressed air, allowing the brakes connected to those circuits to function properly. This design increases safety by maintaining braking capability even if one circuit is compromised. The valve does not protect against excessive pressure; that function is handled by a different component called a pressure relief valve.