- What is Backflow?
- Backflow is the unwanted flow of used or non-potable water or other substance from any domestic, industrial or institutional piping system into the pure, potable water distributions system.
- Why is Backflow Bad?
- Backflow is bad because of the potential for hazardous chemicals to contaminate good drinking water which can result in serious illness.
- Backflow Prevention
- Air Gap: Simple and effective, air gaps are the unobstructed vertical space between the water outlet and the floor level of a fixture. A simple example is the space between a wall mounted faucet and the sink rim. Water can easily flow from the faucet into the sink, but there is no way that water can flow from the sink into the faucet.
- Check Valve: A mechanical device that allows fluid to flow through it in only one direction.
- Double Check Valve: Consists of two check valves assembled in series usually with a ball or gate valve install at each end for isolation and testing. Often, small ball valves are in place to attach test equipment for evaluation whether the double check assembly is still functional. Double check valves are suitable for prevention of back pressure and back siphonage, but not recommended for high hazard applications.
- Atmospheric Vacuum Breakers (AVB): Usually constructed of brass and resembles a 90° elbow with a hood on its top to allow air to enter the water system if a siphon attempts to form. Inside the elbow is a poppet valve that is held up by the water pressure in the system, closing the air entrance to the device. If the pressure in the upstream side is reduced to atmospheric pressure or below, the poppet valve drops and allows air to enter the system, breaking the siphon.
- Pressure Vacuum Breakers (PVB): are similar to atmospheric vacuum breakers, except that the PVB contains a spring-loaded poppet and may be used on high hazard applications and may have valves installed downstream.