Selecting A Backflow Preventer

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Type of Application

The type of application and industry, such as fire protection, irrigation, and plumbing, each have particular requirements. Fire sprinkler systems may require detector bypasses or grooved end gate connections. On the other hand, an irrigation system may require pressure vacuum breakers that are not used universally in other types of systems. In certain critical applications, such as hospitals, resort hotels, or industrial applications, water must be continually supplied. This requires either multiple connections or manifold assemblies.

Each application is also unique in regards to flow requirements. Plumbing and waterworks require consistent flow of water. Irrigation requires flow 2% of the time and the remaining 98% of the time is in a static condition. Fire protection must stand ready for action with 100% static water pressure.

Type of Installation

Installations range from indoor to outdoor and "below grade" or pit installations. Where space is an issue, systems can require a vertical installation. Indoor installations must address the issue of discharge. Of the five standard types of backflow preventers, three spill water, two at start-up and one a basic function of the assembly. Outdoor installations face the potential of vandalism, soil corrosion, and in some climates, freezing temperatures. An outdoor installation may typically require some type of covering.

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Accessibility is often the most overlooked factor in backflow installations. In general accessibility is required for any testing, maintenance or repair. Height requirements for backflow preventers are very specific:

Type of DeviceHeight Requirement
Atmospheric Vacuum Breaker6" above the highest point in the water system downstream
Pressure Vacuum Breaker12" above highest point in the water system downstream
Double Check AssemblyInstalled between 12" - 36" above the floor or finished grade
Reduced Pressure Principal AssemblyInstalled between 12" - 30" above the floor or finished grade

OSHA requires a permanent platform when a valve is installed above 5 feet off the floor.

Side clearance requirement from the wall for Double Check and Reduced Pressure Principal Assemblies (1/2" - 3") are 24" from side testcocks, 12" from top mounted testcocks, with 24" access from one side. For sizes 4" and above, these requirements are doubled.

The weight of the checks must also be considered, especially if you are looking for a vertical installation. The check assembly weight for an 8" or 10" device may require lifting assistance.

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Text courtesy of Wilkins a Zurn company.