Backflow Preventers

There are several backflow preventer types used in residential plumbing and heating applications.

Some of these are:
Vacuum Breakers, Anti-Siphon Mechanisms;
Check Valves;
Backflow Preventer Assemblies;

All of the above serve the purpose of preventing the backflow of water due to pressure differential in liquids or gravity flow.

A typical example of a backflow prevention device in irrigation application is an anti-siphon frost free sillcock. The anti-siphon device built into the sillcock valve prevents the domestic water (used for showering, food preparation, etc.) from being contaminated with lawn irrigation water. This is a particular concern is areas where water supply (garden valve, also known as lawn faucet) is positioned on a lower level than the irrigated area and especially, if any chemicals are used for irrigation purposes.

Backflow preventers are also used in heating systems which have a water feed line, directly connected to the domestic water supply line. A backflow of water in such systems can occur due to difference in pressures between the heating system and a domestic plumbing system. Such differentials constantly occur when circulator pumps start up, or either one of the systems is drained for service.

In heating systems, spring and swing type check valves are used to regulate the flow of water in the system and avoid conflicts between circulators. Another example of a backflow prevention device is Taco Flo-Check valve, which is used to prevent gravity circulation.

According to IAPMO, a leading resource on backflow prevention information, the only mechanical devices capable of preventing both the backflow due to back pressure and back siphonage are dual check valves and pressure reducing assemblies. Always look for an IAPMO/UPC logo when choosing a backflow preventer for your application.