46 CFR §64.59

1. (a)Be set at a nominal pressure of 125 percent of the maximum allowable working pressure;
2. (b)Have a minimum normal venting capacity that is sufficient to prevent the tank pressure from exceeding 137.5 percent of the maximum allowable working pressure;
3. (c)Close after discharge of a pressure not lower than 115 percent of the maximum allowable working pressure; and
4. (d)If closed, remain closed at any pressure less than 115 percent of the maximum allowable working pressure.