(a)
- (1) This section does not contain details of all possible arrangements of boiler blowoff equipment.
- (2) A Guide to Blowoff Vessels, NB-27, governing the installation of blowoff tanks, should be consulted.
- (3) Refer to the National Board of Boiler and Pressure Vessel Inspector’s website for information at nationalboard.org.
- (b) The blowdown from a boiler or boilers that enters a sanitary sewer system or blowdown which is considered a hazard to life or property shall pass through some form of blowoff equipment that will reduce pressure and temperature as required by this subpart.
- (c) All blowoff tanks shall be designed and stamped per the ASME Section VIII, Division 1, for a pressure of at least fifty pounds per square inch gauge (50 psig).
- (d) The temperature of the water leaving the blowoff equipment shall not exceed one hundred fifty degrees Fahrenheit (150° F).
- (e) The pressure of the blowdown leaving any type of blowoff tank shall not exceed five pounds per square inch gauge (5 psig).
- (f) The blowoff equipment shall be fitted with openings to facilitate cleaning and inspection.
- (g) The tank shall be fitted with an opening for a thermometer well, which shall be located close to the water outlet connection and in contact with the retained water in the tank.
- (h) All blowoff tanks shall have a vent to atmosphere of at least the size indicated in Table 1 of this section. TABLE 1 OPENING OF BLOWOFF TANKS PIPE SIZE
| BOILER BLOWOFFLINE | WATER OUTLET | VENT |
| *3/4 | ¾ | 2 |
| 1 | 1 | 2 ½ |
| 1 ¼ | 1 ¼ | 3 |
| 1 ½ | 1 ½ | 4 |
| 2 | 2 | 5 |
| 2 ½ | 2 ½ | 6 |
See Figures TABLE EXPLANATION From the blowoff column, pick the size of pipe which is the smallest size of pipe in the blowoff line from the boiler to the blowoff tank. The size of the water outlet and vent will be that as indicated on the same line of the table. Example: A boiler installation that has a 1 ½-inch blowoff line from the drum to a 2 ½-inch header which leads to the blowoff tank, the size of the water outlet and vent will be determined by the 1 ½-inch size. *To be used only with boilers of 100 sq. ft of heating surface or less. Note: Vent size in the above table is based on the area of extra heavy pipe and is approximately 5 times the area of the blowoff line.