Nevada Administrative Code › Chapter 455C - Boilers, Elevators and Pressure Vessels › BOILERS AND PRESSURE VESSELS › Safety Requirements › Section 455C.232 - Hot water boilers: Safety relief valves

Current through June 11, 2024
1. Each hot
				water heating boiler must have at least one safety relief valve, certified by
				the American Society of Mechanical Engineers or the National Board, set to
				relieve pressure at or below the maximum allowable working pressure of the
				boiler. Each hot water supply boiler must have at least one safety relief valve
				of the automatic reseating type, certified by the American Society of
				Mechanical Engineers or the National Board, set to relieve at or below the
				maximum allowable working pressure of the boiler. Safety relief valves must
				have a capacity certified by the American Society of Mechanical Engineers or
				the National Board and must have a spring-pop type action if tested by steam.
				If more than one safety relief valve is used on hot water heating or hot water
				supply boilers, the additional valve must be rated by the American Society of
				Mechanical Engineers or the National Board and set within a range not to exceed
				6 PSIG above the maximum allowable working pressure of the boiler up to and
				including 60 PSIG and 5 percent if the maximum allowable working pressure
				exceeds 60 PSIG. Safety relief valves must be spring loaded. Safety relief
				valves must be arranged so that they cannot be reset at a higher pressure than
				the maximum permitted by this subsection.
2. Material that is likely to fail because of
				deterioration or vulcanization if it is subjected to a saturated steam
				temperature which corresponds to test pressure for capacity must not be used
				for any part of the safety relief valve.
3. A safety relief valve must not be smaller
				than three-quarters of an inch or larger than 4 1/2 inches in a standard pipe
				size, except that boilers having an input of heat of not more than 15,000
				British thermal units per hour may be equipped with a safety relief valve of
				one-half of an inch in diameter or its equivalent area. The opening for the
				inlet must have an inside diameter approximately equal to, or greater than, the
				diameter of the seat. The minimum opening through any part of the valve must
				not be less than one-fourth of an inch in diameter or an equivalent
				area.
4. The capacity of the safety
				relief valve for each boiler with a single safety relief valve must be such
				that, with the fuel-burning equipment installed and operated at maximum
				capacity, the pressure cannot exceed 10 percent above the maximum allowable
				working pressure of the boiler.
5.
				If operating conditions are changed or additional boiler heating surface is
				installed, the capacity of the valve must be increased, if necessary, to meet
				the new conditions as set forth in the code and must be in accordance with
				subsection 4. The additional valves required because of changed conditions may
				be installed on the outlet piping if there is no intervening valve.
6. If there is any doubt as to the capacity
				of the safety relief valve, an accumulation test must be run as provided in
				section IV of the
ASME Boiler and Pressure Vessel Code
, as
				adopted by reference in NAC
				455C.108.
7. A valve of any description must not be
				placed between the safety relief valve and the boiler, or on the discharge pipe
				between the safety relief valve and the atmosphere. The discharge pipe must be
				at least full size and fitted with an open drain to prevent water from lodging
				in the upper part of the safety relief valve or in the discharge pipe. If an
				elbow is placed on the discharge pipe, it must be located close to the safety
				relief valve outlet or the discharge pipe must be securely anchored and
				supported. All discharges from the safety relief valve must be so located or
				piped as not to endanger any person in the area.
8. A pressure and temperature relief valve
				must be installed on all water heaters and hot water supply boilers to which
				the provisions of NAC
				455C.020 to
				455C.300, inclusive, and section
				1, apply.
Added to NAC by Div. of
				  Industrial Relations by R101-02, eff. 12-15-2004; A by
				  R045-20A,
				  eff. 10/26/2020; A
				  by
				  R034-21A,
				  eff. 7/26/2023
NRS 455C.110