606.5.4 Overflows for water supply tanks.
PC § 606.5.4
A gravity or suction water supply tank shall be provided with an overflow with a diameter not less than that shown in Table 606.5.4. The gallons per minute listed in the table shall be the total automatic pump capacity connected to the tank. The overflow outlet shall discharge at a point not less than 6 inches (152 mm) above the roof or roof drain, or over an open water-supplied fixture. The overflow outlet shall be covered with a corrosion-resistant screen of not less than 16 by 20 mesh per inch (630 by 787 mesh per m) and by 1/4-inch (6.4 mm) hardware cloth or shall terminate in a horizontal angle seat check valve. Drainage from overflow pipes shall be directed so as not to freeze on roof walks. Table 606.5.4Size of Overflows for Gravity and Suction Tanks Overflow Pipe Size(inches)Maximum Allowable GPM for Each Orifice Opening into TankMaximum Allowable GPM for Vertical Overflow(Piping Connecting Orifices)Overflow Pipe Size(inches)Maximum Allowable GPM for Each Orifice Opening into TankMaximum Allowable GPM for Vertical Overflow(Piping Connecting Orifices)2 19 25 3 43 75 4 90 163 5 159 296 6 257 472 8 505 1,020 10 890 1,870 12 1,400 2,967 For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m. Figure 606.5.4Methods of Connecting Overflow from Gravity House and Suction Water Supply Tanks
