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BASIC TYPE OF BACKFLOW PREVENTION DEVICES
Please note: The
following is for information purposes only and does not in anyway mean
these are approved devices. Check with your local code enforcement office
before
selecting your backflow device. |
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Device Type & Use
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Description
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Installed
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Examples
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Illustration
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AIR GAP
High or low health hazard, back-siphon protection. |
Physical separation of potable
and non potable water systems - gap equal to 2 times diameter of supply
line. |
End of supply pipe. |
Pesticide spray tanks, sinks,
any non-pressurized receiver. |
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HOSE CONNECTION VACUUM
BREAKERS
Hose outlets, non continuous pressure |
Single check valve with
atmospheric vacuum breaker vent. Typical size: 3/4 inch hose thread. |
On hose bibbs and service sinks
(no downstream valves). |
Hose bibbs, service sinks,
hydrants. |
 |
ATMOSPHERIC VACUUM BREAKER
High hazard, non continuous pressure or backpressure. |
Single float and disk with large
atmospheric port. Typical sizes: 1/2 inch to 3 inches. |
6 inches above fixture rim, not
subject to backpressure or continuous pressure (Back-siphon protection
only.) |
Pesticide spray tanks,
single-zone lawn sprinklers, washing machines, dishwashers, processing
tanks. |
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PRESSURE-TYPE VACUUM BREAKER
High hazard continuous pressure. |
Spring-loaded single float with
independent first check valve. Shut- off valves and test cocks. Typical
sizes: 1/2 inch to 2 inches. |
12 inches above overflow level
of system being supplied and for continuous supply pressure. (Backsiphon
protection only.) |
Lawn sprinklers, livestock water
systems, pesticide spray tanks and filling systems, swimming pools,
laboratory equipment. |
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DOUBLE-CHECK WITH
INTERMEDIATE VENT
Low hazard, continuous pressure, small pipes. |
Two independent check valves
with intermediate vacuum breaker and relief valve. Typical sizes: 1/4 inch
to 3/4 inch. |
Cross-connections with low
health hazards, subject to back-pressure, back siphonage, backflow and
continuous pressure. |
Small boilers, dairy equipment,
residential small cooling towers. |
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DOUBLE-CHECK VALVE
Low health hazard, continuous pressure. |
Two independent check valves
with various arrangements. Typical sizes: 3/4 inch to 10 inches. |
Cross-connections with low
health hazards, subject to continuous pressure. |
Fire protection sprinklers,
tanks and vats, cookers, supply lines. |
 |
REDUCED PRESSURE ZONE
High hazard, continuous pressure and back pressure back-siphon protection. |
Two independent check valves
with intermediate relief valve. Shut-off valve and test cocks. Typical
sizes: 3/4 inch to 10 inches. |
All cross connections subject to
back pressure or back- siphon and high health hazards continuous pressure. |
Main supply lines, commercial
boilers, hospitals, process tanks, sewage treatment, pesticide handling. |
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