Just like in the human body, pipes are meant to carry liquid only one way. However, pressure changes (from a broken water line or open hydrant for example) in pipes sometimes cause water to flow backwards. This is called backflow, and it can be dangerous. Backflow prevention valves are designed to stop water from flowing the wrong way, but how do they work?
The basic idea is simple. Most people are familiar with one-way valves from everyday life. Even something as common as a garden gate designed to only open out is a type of one-way valve. Backflow prevention valves work on the same principle. Some of them are made for individual homes and are small. However, some of them (like those that require 909 backflow parts) are much larger. The more water that flows into a plumbing system, the bigger the backflow prevention valve needs to be.
Smaller valves may be a lot like the garden gate. A flap with a hinge on one side of an opening rather than another can stop backflow in small systems. If you are ordering 909 backflow parts, though, the system is much bigger, and the design of the vale is different as well. Instead of a flap, rubber stoppers are loaded into springs. The water flowing the right way forces the spring out and the valve open. If water starts flowing backwards, the spring contracts and places the stopper in the pipe’s opening. In doing so, the valve keeps any contamination in the system from getting into the general water supply.
