Nevada Administrative Code › Chapter 455C - Boilers, Elevators and Pressure Vessels › BOILERS AND PRESSURE VESSELS › Safety Requirements › Section 455C.228 - Power boilers: Safety valves

Current through June 11, 2024
1. The use of
				weighted-lever safety valves or safety valves having the seat or disc of cast
				iron is prohibited. Valves of this type or construction must be replaced by
				direct spring-loaded, pop-type valves that conform to the requirements of
				section I of the
ASME Boiler and Pressure Vessel Code
, as
				adopted by reference in NAC
				455C.108.
2. Each boiler must have at least one safety
				valve certified by the American Society of Mechanical Engineers or the National
				Board and, if it has more than 500 square feet of water-heating surface or an
				input of electric power of more than 1,100 kilowatts, it must have two or more
				such safety valves.
3. The valve
				must be connected to the boiler independent of any other connection and
				attached as close as possible to the boiler, without unnecessary intervening
				pipes or fittings.
4. A valve of
				any description must not be placed between the safety valve and the boiler, or
				on the discharge pipe between the safety valve discharge and the atmosphere. A
				discharge pipe must be at least the full size of the discharge of the safety
				valve and fitted with an open drain to prevent water from lodging in the upper
				part of the safety valve or discharge pipe. If an elbow is placed on a safety
				valve or discharge pipe, it must be located close to the outlet of the safety
				valve or discharge pipe and must be anchored and supported securely. All safety
				discharges must be so located or piped as to be carried clear of walkways or
				platforms.
5. The capacity of the
				safety valve of each boiler must be such that the safety valve will discharge
				all the steam which can be generated by the boiler without allowing the
				pressure to which any valve is set to rise more than 6 percent above the
				working pressure if the steam is discharged or 6 percent above the maximum
				allowable working pressure of the boiler, whichever is less.
6. One or more safety valves on every boiler
				must be set at or below the maximum allowable working pressure. The remaining
				valves may be set within a range of 3 percent above the maximum allowable
				working pressure, but the range of the setting of all the safety valves on a
				boiler may not exceed 10 percent of the highest pressure to which any valve is
				set.
7. If two or more boilers
				operating at different pressures and settings of the safety valve are
				interconnected, the lower pressure boilers or interconnected piping must be
				equipped with safety valves of sufficient capacity to prevent overpressure,
				considering the maximum generating capacity of all boilers.
8. In those cases where the boiler is
				supplied with feed water directly from water mains without the use of feeding
				apparatus other than return traps, a safety valve must not be set at a pressure
				greater than 94 percent of the lowest pressure obtained in the supply main that
				feeds the boiler.
9. The relieving
				capacity of the safety valves on any boiler must be checked by one of the
				following methods, and if found to be insufficient, additional valves must be
				provided:
(a) By making an 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 must be
				sufficient to discharge all the steam that can be generated by the boiler
				without allowing the pressure to rise more than 6 percent above the highest
				pressure at which any valve is set and in no case to rise more than 6 percent
				above the maximum allowable working pressure of the boiler. This method must
				not be used on a boiler with a superheater or reheater or on a high-pressure,
				high-temperature water boiler.
(b)
				By measuring the maximum amount of fuel that can be burned and computing the
				corresponding capacity for evaporation or generation of steam upon the basis of
				the heating value of this fuel. These computations must be made as set forth in
				the appendix of section I of the
ASME Boiler and Pressure Vessel
				Code
, as adopted by reference in NAC
				455C.108.
(c) By measuring the maximum amount of feed
				water that can be evaporated.