Pressure protection valves are designed to protect the energy stored in the tanks. There are three types of overflow valves. With return: fitted between two tanks, for example, when the air taken in by the first tank reduces the pressure. No return: to isolate a tank used for air suspension, for example. Thus a major leak from an air spring does not present any risk for the brake system. With limited return: the applications are the same as the version without return, however, a limited return is permitted.