Section 455C.230 - Steam heating boilers: Safety valves1. Each low-pressure steam boiler must have one or more safety valves certified by the American Society of Mechanical Engineers or the National Board which is of the spring-pop type, adjusted and sealed to discharge at a pressure not to exceed 15 PSIG. Seals must be attached in a manner to prevent the valve from being taken apart without breaking the seal. The safety valves must be arranged so that they cannot be reset to relieve at a higher pressure than the maximum allowable working pressure of the low-pressure steam boiler. A body drain that is below seat level must be provided by the manufacturer for all safety valves and safety relief valves and must not be plugged during or after field installation. For safety valves exceeding a 2 1/2-inch pipe size, the drain hole must be tapped not less than 3/8-inch pipe size. For safety valves which are equal to or less than 2 1/2-inch pipe size, the drain hole may not be less than one-quarter of an inch in diameter.2. A safety valve for a low-pressure steam boiler must not be smaller than three-quarters of an inch. The safety valve must not be larger than 4 1/2 inches. The inlet opening must have an inside diameter equal to or greater than the seat diameter.3. The minimum relieving capacity of the valve must be determined by the marking of the capacity on the boiler.4. The minimum valve capacity in pounds per hour must be the greater figure determined: (a) By dividing the maximum output in British thermal units at the boiler nozzle obtained by the firing of any fuel for which the unit is installed by 1,000; or(b) On the basis of the pounds of steam generated per hour per square foot of heating surface as set forth in the following table: | Minimum Pounds of Steam Per Hour Per Square Foot of Heating Surface |
| Boiler Heating Surface: | Firetube Boilers | Watertube Boilers |
| | |
| Hand fired......................................................................................... | .................... 5 | 6 |
| Stoker fired........................................................................................ | .................... 7 | 8 |
| Oil, gas or pulverized fuel fired......................................................... | .................... 8 | 10 |
| Waterwall Heating Surface: | | |
| | |
| Hand fired......................................................................................... | .................... 8 | 8 |
| Stoker fired........................................................................................ | .................. 10 | 12 |
| Oil, gas or pulverized fuel fired......................................................... | .................. 14 | 16 |
5. For the purposes of the table set forth in subsection 4:(a) If a boiler is fired only by a gas that gives a heat value not in excess of 200 British thermal units per cubic foot, the minimum safety valve or safety relief valve relieving capacity may be based on the value given for hand fired boilers in the table set forth in subsection 4.(b) The minimum safety valve or safety relief valve relieving capacity for electric boilers must be 3 1/2 pounds per hour per kilowatt input.6. The safety valve capacity for each steam boiler must be such that, if the fuel-burning equipment is installed and operated at maximum capacity, the pressure cannot rise more than 6 PSIG above the maximum allowable working pressure.7. If operating conditions are changed or an additional boiler heating surface is installed, the valve capacity must be increased, if necessary, to meet the new conditions as set forth in the code. The additional valves required may be installed on the outlet piping if there is no intervening valve.8. If there is any doubt as to the capacity of the safety 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.108.9. 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 and the atmosphere. The discharge pipe must be at least full size and be fitted with an open drain to prevent water from lodging in the upper part of the safety valve or in the discharge pipe. If an elbow is placed on the outlet for the safety valve or the discharge pipe, it must be located close to the outlet or the discharge pipe and must be securely anchored and supported. All discharges from safety valves must be so located or piped as not to endanger any person in the area.Nev. Admin. Code § 455C.230
Added to NAC by Div. of Industrial Relations by R101-02, eff. 12-15-2004