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603.3 Backflow Prevention Devices, Assemblies, and Methods
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Backflow prevention devices, assemblies, and methods shall comply with Section 603.3.1 through Section 603.3.9.
The minimum air gap to afford backflow
protection shall be in accordance with Table
603.3.1.
For SI units: 1 inch = 25.4 mm
Notes:
| 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 |
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).
An
atmospheric vacuum breaker consists of a body, a
checking member, and an atmospheric port.
A double check valve backflow prevention assembly consists of two independently acting
internally loaded check valves, four properly located test cocks, and two isolation valves.
A pressure vacuum breaker backflow prevention assembly consists of a loaded air inlet valve, an internally loaded check valve, two properly located test cocks, and two isolation valves. This device shall be permitted to be installed indoors where provisions for spillage are provided.
A pressure-type vacuum breaker backflow prevention assembly consists of one check valve force-loaded closed and an air inlet vent valve force-loaded open to atmosphere, positioned downstream of the check valve, and located between and including two tightly
closing shutoff valves and test cocks.
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