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The Protection That Is Not a Device

It is the highest protection in EPA’s manual, it costs nothing, and the way it fails has nothing to do with hardware.

Key point

EPA requires an air gap to be twice the supply pipe diameter and never less than one inch. It is the only protection with no moving part and the only one that cannot stick or corrode, and EPA still requires air gaps to be inspected as frequently as mechanical backflow preventers.

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 dimension

EPA states it directly: an air gap must be twice the supply pipe diameter but never less than one inch.

2 × D, minimum 1 inchthe vertical separation between the outlet of a supply and the flood level rim of the vessel receiving it

Two numbers, both easy to check with a ruler, and between them they are the strongest protection in the manual.

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

Why it beats every mechanical device

Because there is nothing to fail. A check valve can foul on a grain of grit and hold slightly open. A relief port can be blocked. A spring can weaken. An air gap is a distance, and distances do not stick, corrode or need a test kit.

It addresses both backsiphonage and backpressure for the same reason: there is no continuous path, so neither a vacuum nor a pressure has anything to act along.

And how it fails anyway

Somebody closes it. A hose is pushed further down. A pipe is extended. A vessel is filled higher than its rim. A flexible line is left hanging into what it is filling.

The failure mode is a person, not a part. Which is why EPA is explicit that air gaps must be inspected as frequently as mechanical backflow preventers — the one protection with nothing to wear out still needs looking at, because the thing that ruins it is somebody being helpful.

Where you already have one

Above a sink, if the faucet spout ends well clear of the rim. On a dishwasher, in that small chrome fitting on the countertop that most people assume is decorative. On many appliance fills.

They are common, they are invisible once you stop noticing them, and they are doing real work.

The thing to watch for

Any arrangement where a supply outlet has been brought down to, or below, the level of what it is filling. A hose in a tank. A fill line into a vessel. A tap with an extension on it reaching into a container.

The most common version of this is in a yard, and several of EPA’s case histories are exactly it.

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