City of Grant gives information on cross connection and blackflow prevention
What is a cross-connection?
A cross-connection is any temporary or permanent connection between a public water system or consumer’s potable (i.e., drinking) water system and source or system containing non-portable water or other substances. An example is the piping between a public water sytem or consumer’s potable water system and an auxiliary water system, cooling system, or irrigation system.
What is backflow?
Backflow is the undesirable reversal of flow of non-potable water or other substances through a cross-connection and into the piping of a public water system or consumer’s potable water system. There are two types of backflow: backpressure backflow and back-siphonage.
Backpressure backflow is backflow caused by a downstream pressure that is greater than the upstream or supply pressure in a public water system or consumer’s potable water system.
Backsiphonage is backflow caused by a negative pressure.
What is a backflow preventer?
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 to backflow.
What types of backflow assemblies, devices and methods are permitted?
The following are types of permitted assemblies, devices and methods: Air gap, atmospheric vacuum breaker, double check valve assembly, pressure vacuum breaker assembly and reduced pressure principle backflow prevention assembly. They may have a specific use depending on the type of cross connection hazard that is present.
Why do backflow preventers have to be tested periodically?
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.
Specific Information about a Hose Bibb Atmospheric Vacuum Breaker
A hose bib vacuum breaker should be attached to all threaded hose bibs’ to which a hose can be connected (unless it has a built-in vacuum breaker). Cross-connections with hoses are probably the most prevalent cause of backflow and the contamination of the water system. These devices do not protect against back pressure, only siphonage. They should be installed above the level of the hose being used on it and not under continuous pressure (12 hours at a time)
For more information contact City of Grant Water Superintendent Gary Beckler (308) 352-6101.