40 CFR Table 31 to Subpart G of Part 63
Typical Number of Vacuum Breakers, NF6 and Roof Drains, NF7
June 9, 2020
Open Table
| Tank diameter D (feet)b | No. of vacuum breakers, NF6 | No. of roof drains, N F7 double-deck roofc | |
|---|---|---|---|
| Pontoon roof | Double-deck roof | ||
| 50 | 1 | 1 | 1 |
| 100 | 1 | 1 | 1 |
| 150 | 2 | 2 | 2 |
| 200 | 3 | 2 | 3 |
| 250 | 4 | 3 | 5 |
| 300 | 5 | 3 | 7 |
| 350 | 6 | 4 | d |
| 400 | 7 | 4 | d |
aThis table should not supersede information based on actual tank data.
bIf the actual diameter is between the diameters listed, the closest diameter listed should be used. If the actual diameter is midway between the diameters listed, the next larger diameter should be used.
cRoof drains that drain excess rainwater into the product are not used on pontoon floating roofs. They are, however, used on double-deck floating roofs, and are typically left open.
dFor tanks more than 300 feet in diameter, actual tank data or the manufacturer's recommendations may be needed for the number of roof drains.
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