Spring loaded pressure relief valve.

A spring loaded pressure relief valve must— (a) Be set at a nominal pressure of 125 percent of the maximum allowable working pressure; (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; (c) Close after discharge of a pressure not lower than 115 percent of the maximum allowable working pressure; and (d) If closed, remain closed at any pressure less than 115 percent of the maximum allowable working pressure.