NAC455C.232. Hot water boilers: Safety relief valves.

     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 10 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 a 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 must be such that, with the fuel-burning equipment installed and operated at maximum capacity, the pressure cannot exceed 6 PSIG above the maximum allowable working pressure of the boiler up to and including 60 PSIG and 10 percent if the maximum allowable working pressure exceeds 60 PSIG.

     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, apply.

     (Added to NAC by Div. of Industrial Relations by R101-02, eff. 12-15-2004)