Section 18(3)(iii) in The Static and Mobile Pressure Vessels (Unfired) Rules, 2016
(iii)where the emergency shut off valve is of the excess flow type, it shall operate at a designated differential pressure and flow rate for size and service as approved by the Chief Controller and its closing rate of flow shall be below the rate which is likely to result from a fracture of the line it is protecting, calculated under the most adverse weather conditions likely to be experienced. Excess flow valves shall have a rated flow capacity sufficiently above normal flow requirement to prevent valve chatter;