What is anti-siphon outdoor faucet?

An anti-siphon outdoor faucet is a type of outdoor faucet designed to prevent backflow or back-siphonage of contaminated water into the potable water supply. It contains a built-in backflow prevention device that complies with plumbing codes and health regulations. Anti-siphon faucets are required by law for most outdoor water applications.

What is backflow and back-siphonage?

Backflow occurs when water flows in the opposite direction from its intended flow, while back-siphonage is a form of backflow caused by negative or reduced pressure in the supply piping. This can allow contaminated water from irrigation systems, pools, ponds etc. to be siphoned back into the drinking water system, posing a health risk.

Some common causes of back-siphonage are:

• Water main break – can reduce pressure in the public water supply
• High water withdrawal rate – from firefighting or broken pipes
• Booster pumps – can create negative pressure
• Elevation – contaminated source located higher than faucet

Backflow prevention devices are designed to avoid these situations by allowing water to flow in only one direction to isolate the drinking water supply from potential contaminants.

Why are anti-siphon faucets required?

Plumbing codes and health regulations require the use of backflow prevention devices or assemblies on outdoor faucets to protect the potable water supply from contamination. The specific requirements can vary based on local jurisdiction, but most mandate the use of anti-siphon faucets or vacuum breakers.

This is because outdoor faucets are high-risk connections to the drinking water system. They can come in contact with chemicals, fertilizers, bacteria from stagnant water sources, or other pollutants. Anti-siphon faucets provide an important barrier to backflow at these hazardous cross-connections.

Types of anti-siphon devices

There are two main types of anti-siphon devices used for outdoor faucets:

Integral anti-siphon valves

These have a built-in backflow preventer as part of the faucet body. The valve only allows water to flow in one direction and will shut off if back pressure occurs. The two common designs are:

• Atmospheric vacuum breaker – Has a floating disc that seals off the water supply if back-siphonage occurs. It opens to allow air in, breaking the vacuum.
• Pressure vacuum breaker – Contains a spring-loaded check valve that only opens when water pressure overcomes the spring. Closes if pressure drops.

Hose bibb vacuum breakers

These are attachments installed at the spout or hose connection of a standard outdoor faucet. They contain a simple float check valve to prevent backflow.

The main types are:

• Watts 9D – Popular dual-check valve design that threads onto faucet.
• Legend HBVB-2 – Can be installed on hose bibbs or sillcocks. Provides protection up to 5 feet height.

The benefit of integral anti-siphon faucets is that backflow prevention is built-in. Hose bibb vacuum breakers can be added to existing standard faucets, but require vigilance to ensure they are installed correctly.

How do anti-siphon faucets work?

Anti-siphon faucets contain a check valve mechanism that only allows water to flow in one direction – from the supply pipes to the spout or hose connection. If water tries to flow backwards, the internal spring-loaded check valve closes to prevent backflow.

Here are the basic steps of how an anti-siphon faucet operates:

1. Faucet is closed – check valve is shut to block water flow
2. Faucet is turned on – water pressure pushes check valve open
3. Water flows from supply to outlet in normal operation
4. If pressure drops or reverse flow occurs, check valve closes
5. Check valve remains closed until forward water pressure resumes

This provides continuous protection against backflow while allowing normal water flow when faucet is turned on. Most anti-siphon faucets also incorporate a manual vacuum breaker valve as an added backflow prevention measure.

Types of check valves used

The check valve is the key functional component of an anti-siphon faucet. The most common types used are:

Spring Loaded Check Valve

Uses an internal spring to hold the valve sealed until water pressure overcomes spring tension. Simple, reliable, and widely used.

Ball Check Valve

Uses a floating ball that is pushed open by water flow and drops shut under back pressure. Less prone to fouling.

Swing Check Valve

Uses a hinged flap that swings open with forward flow. Reverse flow pushes it firmly closed. No springs.

The check valve design affects the opening pressure needed and potential for fouling or wear over time. Combination designs are sometimes used too.

Pros of anti-siphon faucets

Here are some of the major benefits of using anti-siphon faucets:

• Prevent backflow contamination – This is the key purpose, provides vital protection of potable water.
• Require no maintenance – Internal check valves operate automatically with normal use.
• Easy installation – Attach to standard faucet fittings and pipe configurations.
• Long service life – Durable brass construction and minimal moving parts.
• Low cost – Comparable in price to standard outdoor faucets.
• Frost-proof – Design allows water to drain from faucet to prevent freezing damage.
• Comply with codes – Meet plumbing regulations for backflow prevention.

Cons of anti-siphon faucets

The drawbacks or limitations of anti-siphon faucets include:

• Higher initial cost – More expensive compared to non-anti-siphon faucets.
• Reduced water flow – Check valves add some friction loss, decreases flow rate.
• Potential for fouling – Debris buildup can impede check valve sealing and performance over time.
• Need periodic testing – Annual testing ensures check valves function properly.
• American Society of Sanitary Engineering (ASSE) Standards Compliance – Not all models meet ASSE safety standards.
• Vacuum breakers can freeze – Manual vacuum breakers need to be disconnected in freezing weather conditions.

Key specifications to look for

When selecting an anti-siphon faucet, some key features and specifications to look for include:

• ASSE Standard 1019 compliance – Confirms approved backflow prevention design.
• ASSE Standard 1052 compliance – Required for pressure vacuum breaker types.
• Maximum pressure rating – Minimum 150 psi rating for residential use.
• Operation temperature range – At least 33°F to 140°F for frost and scalding protection.
• Flow rate – Should have at least 10 gpm for typical outdoor applications.
• Inlet connection – Standard 3/4″ GHT threads for hose connection.
• Valve material – Durable brass, ceramic, or plastic construction.
• Seal material – Rubber seals for water tightness, allows for some movement.

Certification from bodies like ASSE or CSA indicates reliable backflow prevention and safety.

Installation tips

Anti-siphon faucets must be installed properly to function as intended. Here are some best practices for installation:

• Attach vacuum breaker – If hose bibb style, ensure vacuum breaker is correctly attached.
• Apply plumber’s tape – Wrap threads with Teflon tape to prevent leaks.
• Position vertically – Install faucet in upright orientation for proper check valve function.
• Allow air gap – Leave at least 6″ clearance below faucet mouth to prevent contamination.
• Insulate pipes – Protect supply pipes from freezing with insulation.
• Flush debris – Open faucet fully to flush out any debris after install.
• Test for leaks – Check for any leaks at connections after installing.

Following the manufacturer’s instructions is also highly recommended for proper installation and operation.

Maintenance tips

Basic maintenance is important for anti-siphon faucets to keep them functioning properly over the long-term. Recommended maintenance practices include:

• Annual testing – Have backflow assembly tested yearly by certified technician.
• Regular inspection – Check for leaks, damaged parts, missing vacuum breaker.
• Flush lines – Flush faucet and lines periodically to clear any debris buildup.
• Clean strainer – Remove and clean strainer basket to prevent clogging.
• Lubricate – Use silicone grease on rubber seals and moving valve parts.
• Drain for winter – Disconnect hoses and vacuum breaker, open faucet to drain.
• Replace worn parts – Have certified repair person replace any worn or defective components.

Following the manufacturer’s maintenance guidelines is also recommended. Proactive maintenance ensures the faucet provides long-lasting backflow prevention.

Conclusion

Anti-siphon faucets are a vital component for outdoor water applications to prevent contamination of drinking water from backflow. They contain integral check valves that only allow water to flow in the normal direction. If back-siphonage occurs, the built-in check valve closes to stop reverse flow.

Common types are atmospheric vacuum breakers, pressure vacuum breakers, and hose bibb vacuum breakers. They provide reliable, low-maintenance backflow prevention. Following codes for installation and proper maintenance is key to ensuring these protective faucets keep working over time.

Anti-siphon faucets should be incorporated into all outdoor plumbing applications, especially irrigation systems, to comply with plumbing regulations and ensure public health and safety against the risk of backflow contamination.