Backflow Assemblies, Devices And Methods | |||||
Degree Of Hazard | |||||
Device, Assembly Or Method1 | Pollution (Low Hazard) | Contamination (High Hazard) | Installation2, 3 | ||
Back Siphonage | Back Pressure | Back Siphonage | Back Pressure | ||
Backflow Assemblies, Devices And Methods | |||||
Degree Of Hazard | |||||
Device, Assembly Or Method1 | Pollution (Low Hazard) | Contamination (High Hazard) | Installation2, 3 | ||
Back Siphonage | Back Pressure | Back Siphonage | Back Pressure | ||
Air gap | X | X | See table in this Chapter. | ||
Atmospheric vacuum breaker | X | X | Upright position. No valves downstream. Minimum of 6" or listed distance above all downstream piping and flood level rim of receptor4. | ||
Double check valve backflow preventer | X | X | Horizontal, unless otherwise listed. Requires 1' minimum clearance at bottom for maintenance. May need platform/ladder for test and repair. Does not discharge water. | ||
Pressure vacuum breaker | X | X | Upright position. May have valves downstream. Minimum of 12" above all downstream piping and flood level rim of receptor. May discharge water. | ||
Reduced pressure principle backflow preventer | X | X | X | X | Horizontal unless otherwise listed. Requires 1' minimum clearance at bottom for maintenance. May need platform/ladder for test and repair. May discharge water. |
1 See description of devices and assemblies in this Chapter. 2 Installation in pit or vault requires previous approval by the Superintendent of Public Works. 3 Refer to general and specific requirements for installation. 4 Not to be subjected to operating pressure for more than 12 hours in any 24-hour period. | |||||
Minimum Air Gaps For Water Distribution4 | ||
Fixtures | When not affected by side walls1 Inches (mm) | When affected by side walls2 Inches (mm) |
Lavatories and other fixtures with effective openings3 not greater than 1/2" (13 mm) in diameter | 1" (25 mm) | 11/2" (38 mm) |
Sinks, laundry trays, goose neck bath faucets and other fixtures with effective openings3 not greater than 3/4" (19 mm) in diameter | 11/2" (38 mm) | 21/4" (57 mm) |
Over rim bath fillers and other fixtures with effective openings3 not greater than 1" (25 mm) in diameter | 2" (51 mm) | 3" (76 mm) |
Effective openings3 greater than 1" (25 mm) in diameter | 2 times diameter of effective opening | 3 times diameter of effective opening |
1 Side walls, ribs or similar obstructions do not affect air gaps when spaced from the inside edge of the spout opening a distance greater than 3 times the diameter of the effective opening for a single wall or a distance greater than 4 times the effective opening for 2 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 Note 1 above. The effect of 3 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 which feeds the device or outlet. If 2 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" (25 mm) shall only be approved as a permanent part of a listed assembly that has been tested under actual backflow conditions with vacuums of from 1 to 25" of mercury. | ||
(Ord. 938, 6-3-1991; amd. 1998 Code)