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Cross-Connection Control Frequently Asked Questions |
A cross-connection is any temporary or permanent connection between a public water system orconsumer’s potable (i.e., drinking) water system andany source or system containing nonpotable water or other substances. An example is the piping between a publicwater system or consumer’s potable water system and anauxiliary water system, cooling system, or irrigation system.
Backflow is the undesirable reversal of flow of nonpotable water or other substances through a cross-connection and into the piping of a public water system or consumer’s potable water system. There aretwo types of backflow: backpressure backflow and backsiphonage.
Backpressure backflow is backflow caused by adownstream pressure that is greater than the upstream or supply pressure in a public water system or consumer’spotable water system. Backpressure (i.e., downstream pressure that is greater than the potable water supply pressure) can result from an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both. Increases in downstream pressure can be created by pumps, temperature increases in boilers, etc. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds the amount of water being supplied, such as during water line flushing, fire fighting, or breaks in water mains.
Backsiphonage is backflow caused by a negative pressure (i.e., a vacuum or partial vacuum) in a public water system or consumer’s potable water system.The effect is similar to drinking water through a straw.Backsiphonage can occur when there is a stoppage of water supply due to nearby fire fighting, a break in a watermain, etc.
Backflow into a public water system can pollute or contaminate the water in that system (i.e.,backflow into a public water system can make the water in that system unusable or unsafe to drink), and each water supplier has a responsibility to provide water that isusable and safe to drink under all foreseeable circumstances. Furthermore, consumers generally have absolute faith that water delivered to them through a public water system is always safe to drink. For these reasons, each water supplier must take reasonable precautions to protect its public water system against backflow.
Water suppliers usually do not have the authority or capability to repeatedly inspect every consumer’s premises for cross-connections and backflow protection. Alternatively, each water supplier should ensure that a proper backflow preventer is installed and maintained at the water service connection to each system or premises that poses a significant hazard to the public water system. Generally, this would include the water service connection to each dedicated fire protection system or irrigation piping system and the water service connection to each of the following types of premises: (1) premises with an auxiliary or reclaimed water system; (2) industrial, medical, laboratory, marine or other facilities where objectionable substances are handled in a way that could cause pollution or contamination of the public water system; (3) premises exempt from the State Plumbing Code and premises where an internal backflow preventer required under the State Plumbing Code is not properly installed or maintained; (4) classified or restricted facilities; and (5) tall buildings. Each water supplier should also ensure that a proper backflow preventer is installed and maintained at each water loading station owned or operated by the water supplier.
A backflow preventer is a means or mechanism to prevent backflow. The basic means of preventing backflow is an air gap, which either eliminates a cross-connection or provides a barrier to backflow. The basic mechanism for preventing backflow is a mechanical backflow preventer, which provides a physical barrier tobackflow. The principal types of mechanical backflow preventer are the reduced-pressure principle assembly, the pressure vacuum breaker assembly, and the doublecheck valve assembly. A secondary type of mechanical backflow preventer is the residential dual check valve.
| An air gap is a vertical, physical separation between the end of a water supply outlet and theflood-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 isconsidered the maximum protection available against backpressure backflow or backsiphonage but is not always practical and can easily be bypassed. |  |
| An RP is a mechanical backflow preventer that consists of two independently acting, spring-loaded checkvalves with a hydraulically operating, mechanically independent, spring-loaded pressure differential reliefvalve between the check valves and below the first checkvalve. It includes shutoff valves at each end of theassembly and is equipped with test cocks. An RP iseffective against backpressure backflow and backsiphonage and may be used to isolate health or non-health hazards. |  |
| 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 shut-off 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. |  |
| A DC is a mechanical backflow preventer that consists of two independently acting, spring-loaded checkv alves. It includes shut-off valves at each end of the assembly and is equipped with test cocks. A DC iseffective against backpressure backflow and backsiphonage but should be used to isolate only non-health hazards. |  |
An rdc is similar to a DC in that it is amechanical backflow preventer consisting of two independently acting, spring-loaded check valves. However, it usually does not include shutoff valves, mayor may not be equipped with test cocks or ports, and isgenerally less reliable than a DC. An rdc is effective against backpressure backflow and backsiphonage but should be used to isolate only non-health hazards and is intended for use only in water service connections to single-family homes.
Mechanical backflow preventers have internal seals, springs, and moving parts that are subject to fouling, wear, or fatigue. Also mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow preventers have to be tested periodically to ensure that they are functioning properly. A visual check of air gaps is sufficient, but mechanical backflow preventers have to be tested with properly calibratedgauge equipment.
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