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Backflow is a term in plumbing for an unwanted flow of water in the reverse direction. [1] It can be a serious health risk for the contamination of potable water supplies with foul water . In the most obvious case, a toilet flush cistern and its water supply must be isolated from the toilet bowl.
Backflow preventers are categorized into three groupings: Assembly, Device or Method. With the exception of elimination, these are the only ways one can control backflow from taking place. The eight named backflow assemblies all have two resilient seated isolation/shut off valves with properly located test ports.
Backflow prevention device. The simplest, most reliable way to provide backflow prevention is to provide an air gap.An air gap is simply an open vertical space between any device that connects to a plumbing system (like a valve or faucet) and any place where contaminated water can collect or pool.
A dual check backflow preventer is similar to a double check valve in operation. It has two independent spring-loaded check valves. However, dual check valves usually do not include shutoff valves, may or may not be equipped with test cocks or ports, and is generally less reliable than a double check valve.
The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss.
It is usually constructed of brass and resembles a 90-degree elbow with a hood on its top to allow air to enter the water system if a siphon attempts to form. Inside this elbow is a poppet valve that is held "up" by the water pressure found in the system, closing the air entrance to the device. If the pressure in the "upstream side" is reduced ...