Safety Valves

Safety Valves 1. The use of weighted-lever safety valves, or safety valves having either the seat or disk of cast iron, shall be prohibited after these regulations become effective. Valves of this type or construction shall be replaced by direct, spring-loaded, pop-type valves that conform to the requirements of the ASME Code, Section I. 2. Each boiler shall have at least one safety valve, and if it has more than 500 square feet of water-heating surface, or an electric power input of more than 1100 kw, it shall have two or more safety valves. 3. The valve or valves shall be connected to the boiler, independent of any other steam connection, and attached as close as possible to the boiler, without unnecessary intervening pipe or fittings. Where alteration is required to conform to this requirement, owners or users shall be allowed reasonable time in which to complete the work. 4. No valves of any description shall be placed between the safety valve and the boiler nor on the escape pipe, if used, between the safety valve and the atmosphere, except as provided by applicable sections of the ASME Code. When an escape pipe is used, it shall be at least full size of the safety-valve discharge and fitted with an open drain to prevent water lodging in the upper part of the safety valve or escape pipe. When an elbow is placed on a safety valve escape pipe, it shall be located close to the safety-valve outlet, or the escape pipe shall be anchored and supported securely. All safety-valve discharges shall be so located or piped as to be carried clear from walkways or platforms. 5. The safety-valve capacity of each boiler shall be such that the safety valve or valves will discharge all the steam that can be generated by the boiler without allowing the pressure to rise more than six percent above the highest pressure to which any valve is set, and in no case to more than six percent above the maximum allowable working pressure. 6. One or more safety valves on every boiler shall be set at or below the maximum allowable working pressure. The remaining valves may be set within a range of three percent above the maximum allowable working pressure, but the range of setting of all safety valves on a boiler shall not exceed 10 percent of the highest pressure to which any valve is set. 7. When two or more boilers, operating at different pressures and safety-valve settings, are interconnected, the lower pressure boilers or interconnected piping shall be equipped with safety valves of sufficient capacity to prevent over-pressure, considering the maximum generating capacity of all boilers. 8. In those cases where the boiler is supplied with feedwater directly from water mains without the use of feeding apparatus (not to include return traps), no safety valve shall be set at a pressure higher than 94 percent of the lowest pressure obtained in the supply main feeding the boiler. 9. The relieving capacity of the safety valves on any boiler shall be checked by one of the three following methods and, if found to be insufficient, additional valves shall be provided: a. By making the accumulation test, which consists of shutting off all other steam discharge outlets from the boiler and forcing the fires to the maximum. The safety valve capacity shall be sufficient to prevent a rise of pressure in excess of six percent of the maximum allowable working pressure. This method should not be used on a boiler with a superheater or reheater. b. By measuring the maximum amount of fuel that can be burned and computing the corresponding evaporative capacity (steam-generating capacity) upon the basis of the heating value of this fuel. These computations shall be made as outlined in the Appendix of the ASME Code, Section I. c. By measuring the maximum amount of feedwater than can be evaporated. When either of the methods outlined in (2) or (3) is employed, the sum of the safety valve capacities shall be equal to or greater than the maximum evaporative capacity (maximum steam-generating capacity) of the boiler. 10. The relieving capacity of safety valves for forced-flow steam generators shall be in accordance with the requirements of Section I of the ASME Code.