What is a backflow preventer?

Backflow preventers are mechanical devices that are used to prevent the reversal flow of non-potable of water into the clean water supply.  These devices come in many different shapes and sizes.  Their main goal is to ensure that water only flows in one direction, preventing backflow from irrigation systems, fire suppression systems, or other industrial processes.

There are several different types of backflow preventers but, there are only 4 approved testable devices, here are the 4 main types of backflow preventers:

1. Reduced Pressure Zone Device (RPZ): This device has the most moving parts out of the 4 types and offers protection for high hazard applications.  An RPZ has 2 spring loaded check valves, and a relief valve that is placed between the 2 check valves.

2. Double Check Valve Assembly (DCVA):  A double check valve is pretty self explanatory, the DCVA has 2 independently acting spring loaded check valves.  These devices are only used for low-hazard applications.

3. Pressure Vacuum Breaker (PVB):  These backflow preventers are most commonly found on lawn irrigation systems, they can be used for high hazard applications.  A PVB is made up of a spring loaded check valve, and an air inlet valve.

4. Spill Resistant Vacuum Breaker (SRVB):  These backflow preventers are very similar to the Pressure Vacuum Breaker, they are both made up of a spring loaded check valve and an air inlet valve.  These devices were designed to be installed in indoor applications where water spillage must be kept to a minimum.

Understanding different types of Backflow

In the plumbing industry there are two different types of backflow.  There is back-siphonage and there is backpressure.

Back-siphonage:  Occurs when there is a sudden drop in the water supply pressure which causes a vacuum.  This vacuum can draw contaminated water back into the clean water supply from sources such as irrigation systems, chemical containers, or fire sprinkler lines.  Back-siphonage can occur from firefighting, water main breaks or anything that imposes a significant demand on the water system.  These devices can protect against back-siphonage.

High Hazard:

Reduced Pressure Zone Devices, Pressure Vacuum Breakers and Spill Resistant Vacuum Breakers

Low Hazard:

Double Check Valve Devices

Backpressure:  This can occur when the pressure downstream exceeds the upstream pressure resulting in the reversal flow of water.  Backpressure can happen in instances where a boiler is present, booster pumps are used, or even elevated tanks can have a significant amount of head pressure which can over come the water pressure upstream.  These devices can protect against back pressure.

High Hazard:

Reduced Pressure Zone Devices

Low Hazard:

Double Check Valve Devices

Determining what you need

Determining the type of backflow preventer you need can be very tricky.  There is a multitude of different factors that go into choosing the right device.  Before making any decisions on your own, call Backflow Testing Services for a free consultation today 1-800-691-4990.

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