9.2 Air Gaps, Atmospheric Vacuum Breakers & Hose Connection Protection

The air gap (IPC 608.14.1 and 608.16.1)

An air gap in a water distribution system is the unobstructed vertical distance through free air between the lowest opening of a pipe or faucet supplying water to a tank, fixture or device and the flood level rim of the receptacle. With no moving parts, it protects against backsiphonage and backpressure at any hazard level.

• 608.14.1: the air gap is measured vertically from the lowest end of the potable outlet to the flood level rim. Air gaps meet ASME A112.1.2, and air gap fittings meet ASME A112.1.3.
• 608.16.1: openings and outlets protected by an air gap must have the gap in Table 608.16.1. Openings equipped for hose connection must be protected by a method other than an air gap, because a hose can extend the outlet below the rim.

Table 608.16.1: minimum required air gaps

"Away from a wall" applies where walls or obstructions are spaced from the nearest inside edge of the spout more than three times the effective opening diameter for a single wall, or more than four times it for two intersecting walls. Closer than that, use the "close to a wall" column. Water flowing near a wall clings to it, so more separation is needed.

Worked examples

1. A 3/4-inch fill pipe discharges into a tank. The nearest wall is 6 inches away, which is more than 3 × 3/4 = 2.25 inches. The required air gap is 1-1/2 inches.
2. A 2-inch fill line discharges 4 inches from a single wall, which is less than 3 × 2 = 6 inches. The required air gap is 3 × 2 = 6 inches.
3. A 1-inch outlet is 1-1/2 inches from a concrete wall, which is less than 3 inches. The over-rim filler row applies "close to a wall," so the gap is 3 inches.

Atmospheric vacuum breakers (IPC 608.14.6 and 608.16.4)

An atmospheric vacuum breaker (AVB) has a float check (poppet) and an air inlet. When water flows forward, the poppet rises and seals the air inlet. When supply pressure drops, the poppet falls, seals the inlet side and opens the air port, which breaks the siphon.

• Standards (608.14.6): pipe-applied AVBs meet ASSE 1001 or CSA B64.1.1. Hose-connection vacuum breakers meet ASME A112.21.3, ASSE 1011, ASSE 1019, ASSE 1035, ASSE 1052 or the CSA equivalents. "These devices shall operate under normal atmospheric pressure when the critical level is installed at the required height."
• Height (608.16.4): the critical level of an atmospheric or pressure-type vacuum breaker must be at least 6 inches above the flood level rim of the fixture or device. Pipe-applied vacuum breakers must be at least 6 inches above the flood level rim of the fixture, receptor or device served.
• Location (608.16.4): vacuum breakers may not be installed under exhaust hoods or similar locations that will contain toxic fumes or vapors.
• Backsiphonage only: an AVB gives no protection against backpressure, and Table 608.1 rates it for backsiphonage only.
• No valve downstream: an AVB must not be kept under continuous pressure. For lawn irrigation, 608.17.5 states "valves shall not be installed downstream from an atmospheric vacuum breaker," since a closed downstream valve would hold the AVB under pressure and its poppet could stick shut against the air port. Manufacturers also limit how long an AVB may stay under pressure, often to 12 hours in any 24.

Deck-mounted and integral vacuum breakers (IPC 608.16.4.1)

Approved deck-mounted or equipment-mounted vacuum breakers, and faucets with integral AVBs or spill-resistant vacuum breakers, are installed per the manufacturer and the labeling requirements, with the critical level at least 1 inch above the flood level rim.

Hose connections (IPC 608.16.4.2)

Sillcocks, hose bibbs, wall hydrants and other openings with a hose connection must be protected by:

• an atmospheric-type vacuum breaker;
• a pressure-type vacuum breaker; or
• a permanently attached hose connection vacuum breaker.

Exceptions: water heater and boiler drain valves with hose threads intended only for draining the tank or vessel, and clothes washer supply valves where backflow protection is otherwise provided or built into the machine.

Common hose devices:

• ASSE 1011 hose connection vacuum breaker: screws onto the hose thread. It protects against backsiphonage and low head backpressure, and it is not designed for continuous pressure, such as a hose left pressurized against a closed spray nozzle. Field-installed units have a breakaway set screw that shears off when tightened, so the device cannot be removed. That is how the "permanently attached" requirement is met.
• ASSE 1052 hose connection backflow preventer: Table 608.1 rates it for low head backpressure, rated working pressure, backpressure or backsiphonage.
• ASSE 1019 vacuum breaker wall hydrant: a frost-resistant, automatic-draining wall hydrant with built-in vacuum breaker protection.

Other atmospheric methods

• Flush tank fill valves (415.3.1): an antisiphon fill valve meeting ASSE 1002, with its backflow preventer at least 1 inch above the full opening of the overflow pipe.
• Flushometer valves (415.2): their vacuum breakers meet ASSE 1001 or CSA B64.1.1 and need access.
• Barometric loop (608.14.4): the loop must come before the point of connection and rise 35 feet vertically. It works only as an atmospheric or pressure-type vacuum breaker, against backsiphonage.
• Hand showers (412.2): backflow protection per ASME A112.18.1, or a device meeting ASME A112.18.3.

Air gap or vacuum breaker?