Mississippi Administrative Code › Title 15 - Mississippi Department of Health › Part 10 - Boiler and Pressure Vessel Safety › Subpart 76 - Boiler and Pressure Vessel Safety Act and Rules and Regulations › Chapter 3 - Existing Installations › Subchapter 1 - Power and High Pressure › Rule 15-10-76-3.1.6 - Safety Valves

Current through June 25, 2024
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.