Irrigation Backflow Devices - Quick Overview

In most homes the landscape irrigation system and the potable water system are one and the same -- there is no separation. Here's where the danger comes in. Sprinkler lines lay in gardens and lawns that are often sprinkled with weed killer, pesticides, and other poisons. Irrigation systems occasionally draw water inward (backwards). This phenomenon is known as a siphon or backflow. Backflow can result in contaminated water at a tap inside the home. Is there any wonder why the building code requires that all outside irrigation lines have some sort of anti-siphon protection?

Backflow can be defined as the unwanted reverse flow of any liquid, solid or gas in a piping system. In an irrigation application, this means that water within the irrigation system may find its way back into the potable (drinkable) water system during a backflow incident.

A backflow preventer is a device designed to prevent potable water from being contaminated with non-potable water in the event a cross-connection exists during a condition of backflow.

There are two main types of backflow: Back Pressure and Back Siphonage.

Back pressure is when pressure downstream of the device is greater than the pressure upstream. Water hammer is an example of backpressure.
Back siphonage occurs when a vacuum is created upstream and water gets literally sucked backwards. An open fire hydrant, or water main break can cause back siphonage. Not all backflow devices are created equal.