603.3 Backflow Prevention Devices, Assemblies, and Methods
| FIXTURES | WHERE NOT AFFECTED BY SIDEWALLS1 (inches) |
WHERE AFFECTED BY SIDEWALLS2 (inches) |
|---|---|---|
| Effective openings3 not greater than 1/2 of an inch in diameter | 1 | 11/2 |
| Effective openings3 not greater than 3/4 of an inch in diameter | 11/2 | 21/4 |
| Effective openings3 not greater than 1 inch in diameter | 2 | 3 |
| Effective openings3 greater than 1 inch in diameter | Two times the diameter of effective opening | Three times the diameter of effective opening |
For SI units: 1 inch = 25.4 mm
Notes:
1 Sidewalls, ribs, or similar obstructions do not affect air gaps where spaced from the inside edge of the spout opening a distance exceeding three times the diameter of the effective opening for a single wall, or a distance exceeding four times the effective opening for two intersecting walls.
2 Vertical walls, ribs, or similar obstructions extending from the water surface to or above the horizontal plane of the spout opening other than specified in Footnote 1 above. The effect of three or more such vertical walls or ribs has not been determined. In such cases, the air gap shall be measured from the top of the wall.
3 The effective opening shall be the minimum cross-sectional area at the seat of the control valve or the supply pipe or tubing that feeds the device or outlet. Where two or more lines supply one outlet, the effective opening shall be the sum of the cross-sectional areas of the individual supply lines or the area of the single outlet, whichever is smaller.
4 Air gaps less than 1 inch (25.4 mm) shall be approved as a permanent part of a listed assembly that has been tested under actual backflow conditions with vacuums of 0 to 25 inches of mercury (85 kPa).