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There are several types of devices used to preventing the reverse flow of
backpressure of water. They are:
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An air gap is a vertical, physical separation between the end
of a water supply outlet and the flood-level rim of a receiving vessel. This
separation must be at least twice the diameter of the water supply outlet
and never less than one inch. An air gap is considered the maximum
protection available against backpressure backflow or backsiphonage but is
not always practical and can easily be bypassed. |
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| An RP is a mechanical
backflow preventer that consists of two independently acting, spring-loaded
check valves with a hydraulically operating, mechanically independent,
spring-loaded pressure differential relief valve between the check valves
and below the first check valve. It includes shutoff valves at each end of
the assembly and is equipped with test cocks. An RP is effective against
backpressure backflow and backsiphonage and may be used to isolate health or
non-health hazards. |
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| A PVB is a mechanical
backflow preventer that consists of an independently acting, spring-loaded
check valve and an independently acting, spring-loaded, air inlet valve on
the discharge side of the check valve. It includes shutoff valves at each
end of the assembly and is equipped with test cocks. A PVB may be used to
isolate health or non-health hazards but is effective against backsiphonage
only. |
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| A DC is a mechanical
backflow preventer that consists of two independently acting, spring-loaded
check valves. It includes shutoff valves at each end of the assembly and is
equipped with test cocks. A DC is effective against backpressure backflow
and backsiphonage but should be used to isolate only non-health hazards.
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The University of Southern California became involved in
cross-connection control efforts before most had ever heard of backflow.
Over the years , the Foundation has developed a number of products and services
designed to help water utilities, health agencies, plumbing inspectors, private
contractors and the general public in their cross connection control efforts. USC provides The Manual of Cross Connection Control, they evaluate and approve
backflow devices, maintain a list of certified backflow prevention devices,
train and educate, and continue to conduct research in the field of Cross
Connection Control and Backflow Prevention. The list of approved devices they provide is updated on a periodic basis. For the most recent updates go to
USC Foundation. You will need to
register and the foundation will provide you with a password.
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