Minimum Air Gaps for Generally Used Plumbing Fixtures
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Minimum Air Gap
(inches)
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Fixture
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When Not Affected by Near Wall1
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When Affected by Near Wall2
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Lavatories and other fixtures with effective openings not greater
than 1/2 inch diameter
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1.0
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1.50
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Sink, laundry trays, gooseneck bath faucets and other fixtures
with effective openings not greater than 3/4 inch diameter
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1.5
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2.25
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Over-rim bath fillers and other fixtures with effective openings
not greater than 1 inch diameter
|
2.0
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3.0
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Drinking water fountains, single orifice 7/16 (0.437) inch diameter,
or multiple orifices having total area of 0.150 square inch (area
of circle 7/16 inch diameter)
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1.0
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1.50
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Effective openings greater than 1 inch
|
3
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4
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NOTES:
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1
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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 three times the diameter of the effective opening for a single
wall, or a distance greater than four times the diameter of the effective
opening for two intersecting walls.
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2
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Vertical walls, ribs or similar obstructions extending from
the water surface to or above the horizontal plane of the spout opening
require a greater air gap when spaced closer to the nearest inside
edge of the spout opening than specified in Note 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.
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3
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Two times the diameter of the effective opening.
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4
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Three times the diameter of the effective opening.
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Sizes of Overflow Pipes for Water Supply Tanks
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---|---|---|
Maximum Capacity of Water Supply Line to Tank
(gallons per minute)
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Diameter of Overflow Pipe
(inches ID)
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0 to 50
|
2
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50 to 150
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2 1/2
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100 to 200
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3
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200 to 400
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4
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400 to 700
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5
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700 to 1,000
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6
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Over 1,000
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8
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Cross-Connections Where Protective Devices Are Required,
and Critical Level (C-L) Settings for Vacuum Breakers1
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Fixture or Equipment
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Method of Installation
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Aspirators and ejectors
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C-L at least 6 inches above flood level of receptacle served.
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Dental units
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On models without built-in vacuum breakers, C-L at least 6 inches
above flood-level rim of bowl.
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Dishwashing machines
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C-L at least 6 inches above flood level of machine. Install
on both hot and cold water supply line.
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Flushometers (closet and urinal)
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C-L at least 6 inches above top of fixture supplies.
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Garbage-can cleaning machine
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C-L at least 6 inches above flood level of machine. Install
on both hot and cold water supply lines.
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Hose outlets
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C-L at least 6 inches above highest point on hose line.
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Laundry machines
|
C-L at least 6 inches above flood level of machine. Install
on both hot and cold water supply lines.
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Lawn sprinklers
|
C-L at least 12 inches above highest sprinkler or discharge
outlet.
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Steam tables
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C-L at least 6 inches above flood level.
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Tanks and vats
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C-L at least 6 inches above flood-level rim or line.
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Trough urinals
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C-L at least 30 inches above perforated flush pipe.
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Flush tanks
|
Equip with approved ball cock. Where ball cocks touch tank water,
equip with vacuum breaker at least 1 inch above overflow outlets.
Where ball cock does not touch tank water, install ball cock outlet
at least 1 inch above overflow outlet or provide vacuum breaker as
specified above.
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Hose bibbs (where aspirators or ejectors could be connected)
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C-L at least 6 inches above flood level of receptacle served.
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NOTES:
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1 "Critical level" (C-L) is defined
as the level to which the vacuum breaker may be submerged before backflow
will occur. Where the C-L is not shown on the preventer, the bottom
of the device shall be taken as the C-L.
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Partial List of Cross-Connections Which May Be Subject
to Backpressure
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Chemical lines
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Dock water outlets
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Individual water supplies
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Industrial process water lines
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Pressure tanks
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Pumps
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Steam lines
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Swimming pools
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Tanks and vats: bottom inlets
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Hose bibbs
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