Water Safety and Backflow Prevention

Protecting drinking water, conserving water resources, and providing resilience to all buildings
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Sponsored by WATTS Water Technologies, Inc.
By Celeste Allen Novak, FAIA, LEED AP

Coordinating Project Manuals and Construction Documents

Coordinating information from project manuals provided by mechanical engineers with construction documents is key to a successful cross-connection control program. There are many locations in many types of buildings that require attention as to the location, space, and type of cross-connection control. When specifying these controls, engineers review the applications of cross-connection in a variety of building and landscape areas. These include the types of health hazards present on site and in the building since this will help determine the jurisdiction of local authorities. The location, length, size, and orientation of backflow preventers can impact the amount of area required for installation and testing. Many backflow preventers require the release of water in the valve as part of the test or of normal operation, and therefore a drain to prevent annual flooding. Some assemblies cannot be used in a sub-ground level box as they may become flooded. Exposed components have to be protected from freezing in many climate zones.

There are six basic types of backflow preventers used to protect cross-connections. They can be classified by whether they are non-testable or testable. These include air gaps, barometric loops, atmospheric and pressure vacuum breakers, dual check valves and dual checks with intermediate atmospheric vents, double check valve assemblies, and reduced pressure principle devices.

The normal operation of a device will include the unavoidable impact from external sediments and debris from water sources. Backflow preventers that are harder to repair and replace are more expensive over time; therefore, the cheapest solution is probably not necessarily the correct solution. Some backflow preventers have modular parts or fewer moving parts that can be replaced with locally available components. Some are selected because they are lightweight and can be installed and more easily replaced without extra plumbing staff.

Shown is a performance flow curve.

Flow characteristics may determine the size of the entire plumbing riser system. Although pressure loss is an area of concern for all systems, it is especially critical within a fire prevention system. The engineers will calculate the pressure loss across backflow devices. An incoming water source is not always delivered at a constant pressure and may have many variables. In some cases, a booster pump or larger-diameter piping may need to be installed. Each case and application is unique so copying an “old specification” for a new project can be dangerous.

Selecting Backflow Preventers

Backflow preventers can be classified into two major types: testable versus non-testable devices. These mechanical devices contain check valves designed to allow fluids to flow forward while automatically stopping reverse flow. There can be numerous degrees of hazards of the fluids on the downstream side of backflow preventers, and this will impact the selection of the appropriate device. The specifier will also analyze the size, location, likely failure mode, or the need for constant pressure when selecting a device. Some conditions may require the selection that will allow for a shutoff downstream or meet unique regulatory requirements. The selection of a backflow preventor includes the consideration of the cost, weight, reparability, and maintenance of the device.

Testable backflow preventers are larger devices and usually the most expensive. They are rarely specified for residential containment, though they are often used for isolation of residential lawn sprinkler systems. Most commercial devices are testable and required by regulations to be tested annually and when installed or repaired. The AHJ will determine testing requirements for these devices.

Non-Testable Backflow Prevention Valves

Non-testable backflow prevention valves include the following common types.

Atmospheric vacuum breakers are typically used to isolate an area that poses a health hazards.

Atmospheric Vacuum Breaker (AVB) ASSE 1001

Atmospheric vacuum breakers (AVBs) are typically used to isolate an area that poses health hazards. Typical installations include AVBs on lawn sprinklers, parlor sinks, dishwashers, washing machines, and industrial process tanks. They only protect backsiphonage events, preventing the backflow of non-potable liquids into drinking water.

The breaker is sealed by a float that is raised by the pressure of the drinking water on the upstream side of the valve. In the event of backsiphonage, negative pressure will suck the float down, open the vent, and break the vacuum. At this point, the line will suck in air rather than the potentially contaminated water downstream. Engineers will not specify an AVB when continuous pressure is required. Concerns are that, after a time, the vent float will fail and get stuck in the up position. For this reason, downstream shutoffs are incompatible with this system. They must also be installed a minimum of 6 inches above the flood level rim of the application served unless deck/equipment mounted.

Hose bib vacuum breakers are designed for isolation protection against backsiphonage. These devices are appropriate for use when there is a health hazard.

Hose Bib Vacuum Breaker (HBVB) ASSE 1011

Hose bib vacuum breakers (HBVBs) are designed for isolation protection against backsiphonage. These devices are appropriate for use when there is a health hazard. Hoses are the number-one source of unprotected cross-connection in America. There are many case studies of water contamination through unprotected hose bibs. Hoses can be connected to almost anything and should not be subjected to continuous pressure. These common devices contain a check valve and a diaphragm that is pushed against air vents when pressurized and will recede and open the air vents, breaking the vacuum in the case of backsiphonage conditions.

Dual check valves are specified for residential projects. They are often placed after the water meter.

Dual Check Valve (DuC) ASSE1024

Dual check valves (DuCs) are typically specified for residential projects. They are often placed after the water meter. They are rated for backsiphonage and backpressure, as well as continuous pressure, but cannot be used when there is an application that requires defense against health hazards.

These devices are a combination of dual checks and vacuum breakers. ASSE 1012 is used for non-health hazard conditions, and ASSE1052 and 1035 are both rated to be used when a health hazard is present.

Dual Checks with Atmospheric Vents (VDuC) ASSE 1012/1052/1035

These devices are a combination of dual checks and vacuum breakers. ASSE 1012 is used for non-health hazard, full backpressure, continuous pressure applications, and most commonly used as a residential boiler feed valve. ASSE 1052 and 1035 are both rated to be used for health hazard conditions. Like HBVBs, ASSE 1052 and 1035 devices are only rated for low backpressure and cannot be subjected to continuous pressure. ASSE 1052 is a hose connection backflow preventer that works very similarly to a hose bib vacuum breaker. ASSE 1035 is a laboratory faucet vacuum breaker similar to the hose-connection vented dual check, but with a higher temperature rating and lab faucet connections. These devices will have occasional water discharge and installation should specify drainage.

These carbonator valves are dual checks, and dual checks with atmospheric vents, respectively, but they are made specifically for carbonated beverage dispensers.

Carbonated Beverage Backflow Preventer (CBBP) ASSE 1032/1022

These carbonator valves are dual checks, and dual checks with atmospheric vents, respectively, but they are made specifically for carbonated beverage dispensers. The danger to the plumbing system is that when you mix carbon dioxide with water to make carbonated water (for example, at a soda fountain), you also form carbonic acid. This acid will leach copper out of pipes if it backs up into the plumbing system, and there are several case studies where this exact situation has sent people to the hospital.

 

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Originally published in Architectural Record
Originally published in April 2020

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