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Five Families, Not One Product

They are sold as interchangeable solutions to the same problem. They are not interchangeable, and this page is about what separates them.

Key point

The families are not interchangeable. An air gap is the highest protection and addresses both mechanisms. A reduced pressure principle assembly covers high hazard, a double check valve low to medium. Pressure and atmospheric vacuum breakers address backsiphonage and are not for backpressure.

Source: U.S. EPA, Cross-Connection Control Manual, EPA 816-R-03-002, February 2003.

CrossConnect is a referral service, not a contractor. We connect property owners and managers with independent contractors. Backflow assembly testing is normally restricted to testers holding a specific certification and using calibrated equipment, and the report usually has to reach your water purveyor — ask to see the certification and ask who files the report. We carry out no testing, we certify nobody, we do not set prices, and we never charge callers anything. Nothing here selects a device for any installation or states that any assembly is passing.

The air gap

The highest protection, against both backsiphonage and backpressure, and the only one with nothing mechanical in it. It is a physical separation rather than a device: there is no path for water to travel because there is no pipe.

It has one weakness and it is not mechanical. Why the best protection in the manual is also the easiest to defeat.

Source: U.S. EPA, Cross-Connection Control Manual, EPA 816-R-03-002, February 2003.

Reduced pressure principle assemblies

The mechanical device for high hazard installations, and the one that addresses both backsiphonage and backpressure. It is the assembly most people picture when they hear the phrase: a bronze body, two shutoffs and test cocks.

It has a relief port that discharges when it is doing its job, which is why these need a drain and why they cannot be installed in a pit that floods.

Double check valve assemblies

For low to medium hazard. Two independently acting check valves in series, testable, no relief port.

The distinction between this and a reduced pressure assembly is a hazard judgment rather than a preference, which is why how the hazard gets classified matters more than which device anybody likes.

The two vacuum breakers

Pressure vacuum breakers are used on agricultural and industrial installations and are not for backpressure. Atmospheric vacuum breakers address backsiphonage only and are likewise not for backpressure.

Read that twice if you have irrigation. A device that addresses only one of the two events is a complete answer only where the other event cannot occur, and that is a judgment about the installation rather than about the device.

Which is why we do not pick one

The selection follows from the hazard, the events possible at that connection and the local ordinance, assessed by the purveyor and the plumbing official on the installation itself.

Why a website choosing for you would be doing you harm, given what happens when the choice goes the permissive way.

Know what is on the tag before you call.Make, model, size and the date of the last test are usually stamped or tagged on the assembly itself, and they decide which test kit and which paperwork the visit needs. We will route you to somebody who covers your area, selected on the ZIP code of the property, and you are never charged. Backflow is our specialty, though the number will take any plumbing request on the property.

Call (888) 764-9890