Where is the safety (relief) valve located in an air brake system, and at approximately what pressure is it normally set to open?

Question

Accepted Answer

In the first air tank the compressor fills; it normally opens at about 150 psi

Answer

In the brake chamber at each wheel; it opens at about 55 psi

Answer

In the parking brake control valve; it opens at about 100 psi

Answer

At the treadle (brake pedal) valve; it opens at about 125 psi