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606.5.4 Overflows for Water Supply Tanks
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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 overflow outlet shall discharge at a point not less than 6 inches (152 mm) above the roof or roof drain; floor or floor 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.
SIZES FOR OVERFLOW PIPES FOR WATER SUPPLY TANKS
| MAXIMUM CAPACITY OF WATER SUPPLY LINE TO TANK (gpm) | DIAMETER OF OVERFLOW PIPE (inches) |
| 0 — 50 | 2 |
| 50 — 150 | 21/2 |
| 150 — 200 | 3 |
| 200 — 400 | 4 |
| 400 — 700 | 5 |
| 700 — 1,000 | 6 |
| Over 1,000 | 8 |
For SI: 1 inch = 25.4 mm, 1 gallon per minute = 3.785 L/m.