When parking trailers without spring brakes, it is very important to _________.

The emergency brakes come on whenever the air supply knob is pulled out or the trailer is disconnected. But the brakes will hold only as long as there is air pressure in the trailer air tank. Eventually, the air will leak away, and then there will be no brakes. Therefore, it is very important for safety that you use wheel chocks when you park trailers without spring brakes.