The Difference Between Backflow Preventers and Check Valves

Backflow in plumbing occurs when water or fluids flow in the opposite direction than they should. This is a problem because backflow can allow contaminated water to infiltrate otherwise safe, clean water supplies. Because backflow is a big health and sanitation risk, backflow prevention is a core part of public water safety.

The primary mechanisms to prevent backflow are check valves and the appropriately named backflow preventers. Both prevent backflow, but they are not the same. Consider the differences between backflow preventers and check valves in more detail.

What Is a Check Valve?

A check valve is a simple backflow preventer. Most have a swing or spring-loaded design. The valve remains open as long as the water flows in the correct direction. If the water reverses, the valve shuts, stopping the flow.

The main drawback of check valves is that they are not fail-safe. For example:

• Dirt and debris can clog check valves, preventing them from closing. This can allow dirty water to reverse and cause contamination.
• Check valves are vulnerable to water hammer caused by sudden changes in pressure or flow. The water hammer effect is caused by the valve closing too quickly, which can cause vibrations and pipe damage.

For these reasons, check valves are generally not used alone in drinking water systems. If they are used, it is often in conjunction with backflow preventers.

When Do You Need a Check Valve?

Despite not being appropriate for drinking water systems, check valves work well in many other plumbing setups. You might need check valves for:

• Sump pumps
• Irrigation lines
• HVAC systems and water heaters

Check local code requirements to see where check valves are and are not permissible.

What Is a Backflow Preventer?

A backflow preventer valve is a sophisticated way to stop reversing water from contaminating clean water. There are various types of backflow preventers on the market, including:

• Double Check Valve Assemblies (DCVAs)
• Reduced Pressure Zone (RPZ) Valves
• Pressure Vacuum Breakers (PVBs)
• Atmospheric Vacuum Breakers (AVBs)

Each valve works a bit differently, but they usually include additional protections that make them more effective than check valves. For example, they often stop reverse flow and redirect or dispose of contaminated water. This adds protection that can further reduce contamination risks.

When Is a Backflow Preventer Required?

Backflow preventers are required in a variety of scenarios, given that they are essential to protecting water safety. For example:

• Most cities and towns require them in various locations and mandate regular backflow testing. They’re often built into municipal water systems for this reason.
• Single-family homes also often need backflow prevention devices. This especially includes those with outdoor irrigation systems. In these cases, backflow devices prevent outdoor water from mixing with drinking water.
• Backflow preventers are also common in commercial plumbing, fire sprinkler lines, multi-family homes or systems where chemicals and water may mix. In these spaces, high water demand and frequent pressure changes can increase the risk of backflow, making additional protection necessary.

Backflow Preventers vs. Check Valves: A Side-by-Side Comparison

If you’re wondering what type of backflow management device works for you, here’s a breakdown on how backflow preventers and check valves compare.

	Check Valve	Backflow Preventer
Purpose	To stop reverse water flow in pipes and prevent contamination of clean water.	To stop reverse water flow in pipes and prevent contamination of clean water.
Shape and Size	Often, designs are spring-loaded or swing-door.	Various shapes and sizes including DCVAs, RPZs, PVBs and AVBs.
Fail-Safe Design	No. Valves may clog and fail to shut properly.	More fail-safe. Often have multiple valves and chambers to contain and siphon off backflow.
Level of Protection	Not effective for drinking water systems.	Provides high protection for drinking water.
Risk Level	Higher	Lower
Code Requirements	May be required under certain construction codes.	Usually required in public water systems, commercial buildings, multi-family homes, and irrigation systems. Often needed in single-family homes.
Maintenance/Testing Needs	Require regular maintenance and testing to prevent clogs and valve deterioration.Testing may be required under local law.	Local law often mandates regular maintenance and testing.

Why Backflow Prevention Matters for Raleigh Homes & Businesses

Backflow prevention stops healthy water from being contaminated with bacteria, human waste, fertilizer and toxins. For these reasons, backflow prevention is a benchmark of residential and commercial plumbing water protection throughout the U.S., including the North Carolina Research Triangle. Municipal water providers in Raleigh, Durham, Cary and other area cities enforce backflow prevention requirements, although regulations and codes vary.

If your home or business requires a backflow prevention or check valve system, maintaining the right setup can help you avoid potential fines and water service interruptions. It’s best to work with licensed plumbing experts to select an appropriate backflow solution.

How CK’s Plumbing & Backflow Can Help

CK’s Plumbing is the licensed backflow plumber to trust in Wake County, Durham County and the surrounding region. We offer a full range of commercial and residential plumbing services to keep your water systems clean, sanitary and functional. Contact us today to schedule a backflow test or request a free in-home plumbing estimate.