ASSE 1055 devices are as effective as ASSE 1001 devices for protecting against high‐hazard substances entering the potable water system. Most devices consist of an elastomeric gap (e.g. e‐gap, flex gap, etc.) acting as a check valve that vents to atmosphere when the device is not under pressure. They protect against backsiphonage and low levels of backpressure up a head height equal to the length of hose supplied.

When attached to a faucet that contains an internal ASSE 1001 or ASSE 1011 device, they must have a pressure bleed device as a part of that connection, and the faucet be shut off when not in use. Otherwise the vacuum breaker would be under continuous pressure and that is not the intent of those device designs. It is critical that local jurisdictions mandate and enforce this as this is an installation requirement and not a performance requirement within ASSE 1055.