Backflow preventers are essential devices that protect your drinking water from contamination. There are several types of backflow preventers, each designed for specific plumbing applications. Understanding these types helps homeowners ensure their water supply remains safe and code-compliant. Whether you're dealing with a sprinkler system or a commercial building, choosing the right backflow prevention device is critical. In this guide, we'll explore the main types of backflow preventers, how they work, and when to use each.
What Is Backflow and Why Prevent It?
Backflow occurs when water flows opposite to its intended direction, potentially pulling contaminants into the clean water supply. This can happen through backpressure (when downstream pressure exceeds supply pressure) or backsiphonage (when supply pressure drops). Contaminants such as pesticides, fertilizers, bacteria, and chemicals can then enter your drinking water. According to the EPA's WaterSense program, proper backflow prevention is critical for protecting public health. Local plumbing codes usually require approved devices at cross-connections, such as irrigation systems, fire sprinklers, and commercial kitchens.
Main Types of Backflow Preventers
Each type of backflow preventer is designed for a specific risk level and application. Below are the most common devices found in residential and light commercial plumbing.
Atmospheric Vacuum Breaker (AVB)
An AVB is a simple, low-cost device that prevents backsiphonage. It consists of a check valve and an air inlet that opens when pressure drops, allowing air to break the siphon. AVBs must be installed at least six inches above the highest downstream outlet and cannot be used under continuous pressure. They are commonly found on outdoor faucets and irrigation systems.
Pressure Vacuum Breaker (PVB)
A PVB is similar to an AVB but includes a spring-loaded check valve and can be used under continuous pressure. It also has test cocks for annual testing. PVBs are frequently installed on residential irrigation systems and are effective against backsiphonage but not backpressure.
Double Check Valve Assembly (DCVA)
A DCVA consists of two independently operating check valves with isolation valves and test cocks. It provides protection against both backpressure and backsiphonage for low to moderate hazard conditions. It is common for fire sprinkler systems and some commercial applications, but not for high-hazard situations because it lacks a relief valve.
Reduced Pressure Zone (RPZ) Valve
An RPZ is the most reliable backflow preventer, offering the highest level of protection. It contains two check valves and a differential pressure relief valve that opens to discharge water if the zone between the valves drops below supply pressure. This ensures that any leakage is directed away. RPZs are required for high-hazard applications, such as medical facilities, chemical labs, and irrigation systems with fertilizer injectors. They require annual testing by a certified professional.
Spill‑Resistant Vacuum Breaker (SVB)
An SVB is a variation of a PVB that prevents water spillage during operation. It includes a diaphragm‑type check valve and is often used where aesthetics matter, such as in exposed installations on residential properties.
| Type | Mechanism | Typical Use | Pros | Cons |
|---|---|---|---|---|
| Atmospheric Vacuum Breaker | Air inlet valve | Outdoor faucets, low‑risk irrigation | Low cost, simple | Not under continuous pressure, backsiphonage only |
| Pressure Vacuum Breaker | Spring‑loaded check valve + air inlet | Residential irrigation systems | Continuous pressure, testable | Backsiphonage only, requires testing |
| Double Check Valve Assembly | Two check valves | Fire sprinklers, low‑hazard commercial | Protects against backpressure and backsiphonage | Not for high‑hazard, no visible relief |
| Reduced Pressure Zone Valve | Two checks + differential relief valve | High‑hazard, chemical injection | Highest protection, certified for any hazard | Higher cost, annual testing, occasional discharge |
| Spill‑Resistant Vacuum Breaker | Diaphragm check valve | Exposed residential irrigation | No spillage during operation | Backsiphonage only, more expensive than AVB |
How to Choose the Right Backflow Preventer for Your Home
Selecting the correct device depends on several factors. Use the following checklist to guide your decision:
- Local plumbing codes: Your municipality may mandate specific types for certain applications. Always check with your local building department. The International Association of Plumbing and Mechanical Officials (IAPMO) provides model codes adopted by many jurisdictions.
- Hazard level: High‑hazard connections (e.g., irrigation with fertilizers) require an RPZ. Low‑hazard connections (e.g., a single outdoor faucet) may use an AVB or PVB.
- Application: Irrigation systems often use PVBs or RPZs. Fire sprinklers typically require DCVAs or RPZs depending on local code.
- Maintenance: RPZs and DCVAs need annual testing by a certified backflow tester. AVBs rarely require maintenance beyond visual inspection.
- Cost: Prices vary by region and complexity. In the US, installation of a backflow preventer typically ranges from a few hundred to over a thousand dollars. An AVB is the least expensive, while an RPZ is the costliest.
Installation and Maintenance Considerations
Improper installation can render even the best device ineffective. Always hire a licensed plumber familiar with local backflow regulations. For example, our team at MyTownPlumber specializes in leak detection and can also handle backflow preventer installation. Annual testing is often required for DCVAs and RPZs; certified testers check valve integrity and ensure the relief valve functions correctly. Regular drain cleaning can help prevent clogs that contribute to backpressure. For other plumbing needs such as water heater repair, trust our experienced technicians.
Frequently Asked Questions
What is the most common backflow preventer for residential irrigation?
Pressure vacuum breakers (PVBs) are the most common for residential irrigation because they can handle continuous pressure and are relatively affordable. However, if your system injects chemicals, a reduced pressure zone (RPZ) valve is required.
Do I really need a backflow preventer on my outdoor faucet?
Yes. Many local codes require an atmospheric vacuum breaker (AVB) or an integral vacuum breaker on outdoor spigots to prevent garden hoses from siphoning contaminants into your drinking water.
How often should backflow preventers be tested?
Reduced pressure zone valves and double check valve assemblies typically require annual testing by a certified backflow tester. PVBs may also need testing every year depending on local regulations. AVBs rarely require testing but should be inspected visually.
Can I install a backflow preventer myself?
While some simple devices like an AVB can be a DIY project, most backflow preventers require professional installation to ensure proper sizing, positioning, and compliance with local codes. Incorrect installation can lead to contamination and costly fines.
What is the difference between an RPZ and a DCVA?
A DCVA uses two check valves without a relief valve, making it suitable only for low to moderate hazards. An RPZ adds a differential pressure relief valve that actively discharges water if the check valves leak, providing the highest level of protection for high‑hazard applications.
Will a backflow preventer affect my water pressure?
Most backflow preventers create a slight pressure drop due to the internal check valves. RPZs can cause a more noticeable drop (typically 5–10 psi) because of the relief valve design. If your water pressure is already low, consult a plumber to ensure adequate flow.
Protect your home's water quality with a professionally installed backflow preventer. Contact MyTownPlumber today for expert consultation and installation. Schedule a consultation now.