04-C Cross-Connect/Backflow - Laserfiche WebLink

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What is Backflow and what are Cross-Connections? The term backflow means any unwanted reverse flow of used or non-potable water or subsk-uice from any domestic, industrial or institutional piping system into the safe and clean, potable (drinkable) water distribution system. Backflow may be caused by any number of specific conditions; but basically the reverse pressure gradient is typically caused by either a loss of pressure in thc supply main called backsiphonage, or by pressurized flow from the customer s system, Nchich is called backpressure. When either of these situations occurs in an unprotected system, the water at the point of use can pollute or contaminate the remainder of the wstomer's system. It is also quite possible for this backflow of contaminated water to coniinue on through the customer's meter into the public distribution system creating a potential health hazazd to others. The point at which a non-potable substance can come into contact with the potable drinking water system is known as a cross-connectioa To prevent backflow from occurnng at the poin[ of a cross-connecUoq a backflow prevention assembly must be installed. The type of backflow prevention assembly used must match the particular hydraulic condiuons at that location and be suitable to protect against the degree of hazard present. Some condiUOns require a backflow prevention device on the incoming water line to the entire facility and this form of protection is known as premises isolation. Other conditions require backflow prevcntion devices at Ihc point of the cross-connection and this form of protection is kno«m as internal protection. In many situations, botli forms of backflow protccdon are required to protect both the customer's system and the public water supply system. Types of Backflow Prevention Devices Reduced Pressure Principal Assembly (RP or RPBA): This assembly consists of rivo internally loadcd independcntly opcrating check valves and a mechanically independent, hydraulically depcndant relief valve locatcd bcRvccn the eheck valves. Provides protection against both backsiphonage and backpressure under all hazard condiTions. Double Check Valve Assembly (DC or DCVA): This assembly consists oftrvo internally loaded independently operaUng check valves. Provides protection against both backsiphonage and backpressure but is not considered adequate protection under health hazard conditions. Air Gap (AG): A physical separation between the potable water supply line and the receiving vesscl. Thc air gap scparation must be at least hvice the diameter of the supply line above the receiving vessel with a minimum separadon of one inch. Provides proteclion against both backsiphonage and backpressure under all hazard conditions. ln a pressurized system, an air gap is not feasible and a Reduced Pressure Principal Asscmbly (RPBA) must bc used. An air gap is the only acceptable means of protcction against a direct comiection to radioactive material or sewagc. Pressure Vacuum Breaker (PVB): This assembly consists of an internally loaded check valve vnd a loaded air inlet valve. Providcs protection against backsiphonage only and cannot bc used in situations subject to backpressure. Atmospheric Vacuum Breaker (AVB): This assembly consisu of a"float check" which acts as a check valve and an air inlet valve. Provides protection against backsiphonage only and cannot be used in situaUOns subject to backpressure. The AVB must be installed at least six inches above all downstream piping and outlets to preven[ backpressure. NOTE: Simple Double Check Valves and Single Check Valves are not testable assemblies and are oot approved for protection against any backflow conditions.