How Does an Anti-Siphon Faucet Work?

Vacuum Breaker

• The vacuum breaker portion of the faucet is housed in the anti-siphon valve on the faucet, which has a colored plastic cap on it. The anti-siphon valve sits on the top of the faucet, near the faucet’s water control handle. The vacuum breaker introduces air into the faucet, which does not obstruct the flow of water out of the faucet’s spout. The vacuum breaker does, however, keep water from siphoning or flowing backward through the faucet and into the water supply pipe.

Dangers of Siphoning

• Siphoning presents a danger to the health of anyone who uses your house’s plumbing to cook or for drinking water. When a garden hose is hooked up to an exterior water faucet that does not have an anti-siphon valve, not all of the water drains out of the garden hose after you use it. Instead, some water stays in the hose, where the water heats up. The inside of the garden hose becomes a breeding ground for bacteria, so if the water siphons back into the house’s plumbing, it can spread bacteria into the water supply.

Valve Stem

• Anti-siphon faucets also protect against the water freezing when outside temperatures dip below the freezing point. The valve stem used in the faucet is longer than in other faucets that are not freeze-proof. The longer stem keeps the water further back in the water supply pipe inside the house, where the temperatures do not reach freezing. If the rubber washer on the end of the valve stem wears out and allows water to leak, the water may then freeze and expand, causing the faucet or the water line to expand and rupture.

Other Parts

• The anti-siphon faucet has a twisting water-control handle you move clockwise to decrease or shut off the flow of water coming out of the faucet, or that you turn counterclockwise to increase the flow of water. The handle is attached to the valve which it turns to increase or decrease the opening in the water supply pipe that allows water to flow through. A shutoff valve sits on most water supply lines, which you tighten to cut off the flow of water to the faucet.