Under normal circumstances, the four-loop protection valve is actually a five-way joint, only a primary circuit is broken, leakage failure to play a protective role. Function: When one circuit in the gas braking system fails, the four-protection valve can prevent the inflation and gas supply of other circuits. The four-circuit protection valve divides the whole vehicle gas circuit into four circuits that are interrelated and independent. When any circuit fails (such as break or leakage), the normal work and inflation of other circuits will not be affected.