Minimum Air Gaps for Generally Used Plumbing
Fixtures
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---|---|---|---|
Minimum Air Gap
(inches)
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Fixture
|
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
|
1.0
|
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
|
1.5
|
2.25
| |
Over-rim bath fillers and other fixtures with
effective openings not greater than 1-inch diameter
|
2.0
|
3.0
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Drinking water fountains: single orifice 7/16-inch
(0.437) diameter or multiple orifices having total area of 0.150 square
inch (area of circle 7/16-inch diameter)
|
1.0
|
1.50
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Effective openings greater than 1 inch
|
3
|
4
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NOTES:
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1Side walls, ribs
or similar obstructions do not affect air gaps when spaced from the
inside edge of the spout opening at 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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2Vertical 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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3Two times the diameter
of the effective opening.
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4Three times the
diameter of the effective opening.
|
Sizes of Overflow Pipes for Water Supply
Tanks
| ||
---|---|---|
Maximum Capacity of Water Supply Line
to Tank
(gallons per minute)
|
Diameter of Overflow Pipe
(inches inside diameter)
| |
0 to 50
|
2
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50 to 150
|
2 1/2
| |
100 to 200
|
3
| |
200 to 400
|
4
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400 to 700
|
5
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700 to 1,000
|
6
| |
Over 1,000
|
8
|
Cross-Connections Where Protective Devices
Are Required and Critical Level (C-L)
Settings for Backflow Preventers1
| ||
---|---|---|
Fixture or Equipment
|
Method of Installation
| |
Aspirators and ejectors
|
C-L at least 6 inches above flood level of receptacle
served
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Dental units
|
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
|
C-L at least 6 inches above flood level of machine;
install on both hot and cold water supply line
| |
Flushometers (closet and urinal)
|
C-L at least 6 inches above top of fixture supplies
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Garbage can cleaning machine
|
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
|
C-L at least 6 inches above highest point on
hose line
| |
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
| |
Steam tables
|
C-L at least 6 inches above flood level
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Tank and vats
|
C-L at least 6 inches above flood level rim
or line
| |
Trough urinals
|
C-L at least 30 inches above per- forated 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 out- let at least 1 inch above overflow outlet or provide
vacuum breaker as specified above
| |
Hose bibbs (where as- pirators or ejectors could
be connected)
|
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 backflow preventer (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 Back Pressure
| |
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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 waterlines
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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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Tank and vats, bottom inlets
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Hose bibbs
|