Backflow Prevention Devices

Backflow Prevention Devices (BFPD) Backflow prevention is required by local Municipal Health Codes to prevent contamination of water supplies from irrigated water moving backwards through the irrigation system and into the domestic water line. Codes change from region to region and from city to city. Local Backflow Prevention codes must be complied with or potential serious litigation could result if an incident were to occur. There are generally 5 types: Atmospheric Vacuum Breaker Pressure Vacuum Breaker, Dual check Valve Double Check Valve Reduced Pressure Backflow Device ATMOSPHERIC VACUUM BREAKER This is the simplest form of BFPD. It relies on gravity to close a gate which prevents backflow and back siphonage from occurring. This device does not prevent back pressure and should not be used where back pressure can potentially be an issue or where the AVB is under pressure for long periods of time. AVB’s are not testable. AVB’s must be installed 150mm above the highest downstream sprinkler and on the sprinkler side of any valve. Typically there is one AVB for every zone. These devices are rarely used in irrigation anymore due to their high numbers and lack of efficiency. The hose connection vacuum Breaker (HCVB) is a sub-group of the Atmospheric type vacuum breakers. They are becoming more common in newer housing subdivisions in urban areas. These breakers are typically attached (permanently) to a hose bib on the side of a house. They are designed to provide minimal backflow prevention and are only good for minor amounts of backpressure ie. When a hose end out in the yard is higher than the hose bib at the house, you can get some minor back pressure. HCVB’s are designed so that when a hose tap is shut off, the spring loaded check valve inside closes, opening a vent to the outside allowing air into the downstream side of the hose. HCVBAVB PRESSURE VACUUM BREAKER The Pressure Vacuum Breaker (PVB) was the standard of the residential irrigation industry in the 1960-80’s It relies on a spring loaded gate to prevent backflow/back siphonage from occurring. These devices may still be seen on older residential irrigation systems but have been replaced with newer and better technology. https://www.sprinklerwarehouse.com/pressure-vacuum-breaker-pvb-s/8300.htm https://www.ebay.com/itm/FEBCO-765-1-1-BACKFLOW-PREVENTER-PRESSURE-VACUUM-BREAKER-PVB-BACK-FLOW-765EBV-/280774994087 https://www.thespruce.com/pressure-vacuum-breaker-basics-2718896 DUAL CHECK VALVE Dual check valves cannot be pressure checked so are not legal in new residential installations. They rely on two spring loaded check valves, which only allow water to flow in one direction. Dual check valves are normally installed “in-line” on the supply line to the irrigation system. Typically there is one Dual Check in an irrigation system. https://www.supplyhouse.com/Watts-0122588-LF07S-LF-1- Residential-Fire-Sprinkler-Dual-Check-Backflow-Preventer-Lead-Free https://www.monroevillewater.org/dep- cross-connection-guidelines DOUBLE CHECK VALVES Double Check Valves are a bigger and stronger version of the Dual check valve. They are more reliable as the valves are offset. A Double check valve normally has large isolating gate valves and small detector valves to expel water for testing. Each side of the valve can be closed, isolated and individually checked for performance. They should be inspected annually for proper performance by a certified Cross Connection Certificate holder or plumber. Double check valves are now the standard for most BFPD codes and are very common in residential systems. Double Check Valves protect against both back siphonage and backpressure and can be under constant pressure. This should only be used for low hazard applications. No chemicals. http://www.wattscanada.ca/pages/_products_details.asp?pid=7208 Accessed May 29, 2018 © 2018 Watts https://www.pro-tekmechanicalinc.com/back-flow-prevention accessed May 29, 2018 REDUCED PRESSURE BACKFLOW PREVENTER The most sophisticated form of BFPD is called the Reduced Pressure Backflow Preventer. This is similar to a Double Check valve (large isolation valves, small detector valves for testing) but it has a chamber between the two check valves that is normally about 2 psi lower than the operating pressure of the system. This lower pressure zone prevents water from moving backwards throughout the valve. The Reduced Pressure BFPD is becoming more common despite its high initial expense and maintenance costs. The RP device provides the highest level of protection and is usually on public works projects and municipalities https://encyclopedia2.thefreedictionary.com/reduced-pressure-principle+backflow+preventer accessed Feb 2018 https://www.amazon.ca/Zurn-2-975XL-Pressure-Backflow-Preventer/dp/B00KI0WK7 https://everestplumbing.ca/pros-cons-of-backflow-preventer-installation/ https://mycanyonlake.com/water-company-advises-customers-to-check-backflow-preventers-ahead-of-freeze/ indoor installation outdoor installation cannot be submerged at any time (modified from a handout for LHAP Irrigation by Dennis McKernan Lifeworks Inc ver 3.0)