What Is a Double Check Valve Assembly and Where Is It Required?

If you own commercial property, manage an irrigation system, or have a fire sprinkler connection in Texas, there's a good chance you have a double check valve assembly (DCVA) somewhere on your property. It's one of the most widely installed types of backflow preventers, and it's required in a lot of situations — but not all of them.

We're 1-A Services, a family-owned backflow testing and repair company based in Boyd, TX. We test and repair DCVAs every day across the DFW Metroplex and beyond. Let's break down what this device is, how it works, and where you're likely to need one.

What Is a Double Check Valve Assembly?

A double check valve assembly is a type of backflow prevention device that uses two independently operating check valves to prevent water from flowing backward through a cross-connection and into the public water supply. It's called "double check" because it has two check valves in series — if one fails, the other provides backup protection.

The basic components of a DCVA include:

Two check valves: Spring-loaded valves that allow water to flow in one direction (from the supply side to the downstream side) but close automatically if water tries to flow backward
Two shut-off valves: Gate valves or ball valves on either end of the assembly that allow the device to be isolated for testing and repair
Four test cocks: Small valves used by licensed testers to connect their test equipment and measure the performance of each check valve
A body: The main housing, typically made of bronze, brass, or stainless steel depending on the manufacturer and size

DCVAs come in sizes ranging from 3/4 inch to 10 inches or larger. The size is matched to the water line it's installed on. Residential irrigation systems typically use 3/4" to 1" devices, while commercial and fire line applications may use 2" to 10" devices.

How Does It Work?

Under normal conditions, water flows through the DCVA from the supply side to the downstream side. The water pressure pushes both check valves open, and water passes through freely. You won't notice any significant pressure drop during normal operation.

If a backflow condition occurs — meaning the pressure on the downstream side exceeds the pressure on the supply side — the check valves close. The springs inside each check valve push the valve disc against its seat, creating a watertight seal that prevents water from flowing backward.

Because there are two check valves, the system has redundancy. If the first check valve fails to seal completely (due to debris, wear, or a damaged seat), the second check valve still provides protection. This double layer of protection is what makes the DCVA reliable for the applications where it's approved.

DCVA vs. RPZ: What's the Difference?

The other common backflow preventer you'll encounter is the Reduced Pressure Zone (RPZ) assembly. Understanding the difference between a DCVA and an RPZ is important because they're not interchangeable — each is required for different hazard levels.

Double Check Valve Assembly (DCVA)

Two check valves, no relief valve
Approved for low-hazard and moderate-hazard cross-connections
If both check valves fail, there's no additional safety mechanism
Can be installed in a vault (below grade) or above ground
Generally less expensive than an RPZ
Does not discharge water during normal operation

Reduced Pressure Zone (RPZ) Assembly

Two check valves plus a relief valve
Approved for high-hazard cross-connections
If both check valves fail, the relief valve opens and dumps water to prevent backflow
Must be installed above ground (because the relief valve needs to discharge freely)
More expensive than a DCVA
The relief valve may discharge water periodically during normal operation

The key distinction is the hazard level. A low-hazard cross-connection is one where a backflow event would introduce non-toxic but undesirable substances into the water supply (like irrigation water or water from a cooling system). A high-hazard cross-connection is one where backflow could introduce toxic, chemical, or biological contaminants (like from a chemical plant, medical facility, or sewage connection).

Where Is a DCVA Required?

In Texas, the specific backflow device required for a given connection is determined by the local water utility's cross-connection control program, which follows TCEQ guidelines and the city's own ordinances. Here are the most common applications where a DCVA is required or approved:

Irrigation Systems

This is probably the most common application for DCVAs in Texas. If your property has an in-ground irrigation system connected to the municipal water supply, most cities require a backflow preventer. For standard residential and commercial irrigation (no chemical injection), a DCVA is typically the approved device. Some cities may require a pressure vacuum breaker (PVB) instead, depending on the installation configuration.

Fire Sprinkler Systems (Low Hazard)

Fire sprinkler connections where the system contains only potable water (no antifreeze, no chemical additives) are often classified as low-to-moderate hazard. In these cases, a DCVA may be approved. However, many cities in Texas are moving toward requiring RPZ assemblies on all fire line connections regardless of hazard level, so check with your local water utility.

Commercial Domestic Water Services

Some cities require a backflow preventer on the main domestic water service to commercial buildings. If the building is classified as a low-to-moderate hazard (like an office building or retail space), a DCVA may be the required device.

Boiler Makeup Water Lines

Water lines feeding boilers in commercial buildings often require backflow protection. Depending on the boiler type and the chemicals used in the water treatment, a DCVA or RPZ may be required.

Cooling Tower Makeup Lines

Similar to boilers, cooling towers that use chemical treatment may require backflow protection on the makeup water line. The hazard classification determines whether a DCVA or RPZ is needed.

Where Is a DCVA NOT Sufficient?

There are situations where a DCVA is not adequate and an RPZ or other high-hazard device is required:

Chemical feed or injection systems: Any connection where chemicals are added to the water
Medical and dental facilities: Due to the potential for biological contamination
Mortuaries and funeral homes: High biological hazard
Sewage or wastewater connections: Highest hazard level
Industrial processes: Where toxic chemicals or substances may contact the water
Fire sprinkler systems with antifreeze: The antifreeze creates a high-hazard condition

If you're not sure whether your connection requires a DCVA or an RPZ, your city's cross-connection control department can tell you. Or give us a call — we deal with this every day and can help you figure out what's required.

Annual Testing Requirements

Like all backflow prevention assemblies in Texas, DCVAs must be tested annually by a licensed backflow tester. The test verifies that both check valves are holding at least 1.0 psid (pounds per square inch differential) — meaning each valve creates a measurable pressure barrier against backflow.

If either check valve fails to hold 1.0 psid, the device fails the test and needs repair. Common repairs include replacing check valve springs, rubber seats, or o-rings. These are typically straightforward repairs that can be done on-site in under an hour.

After repair, the device is retested to confirm it's now passing, and the passing report is submitted to the city.

We Test and Repair DCVAs Every Day

At 1-A Services, double check valve assemblies are a core part of our daily work. We test them, repair them, and when they're beyond repair, we replace them. We carry common repair parts on our trucks so we can often handle repairs on the same visit as the test — saving you time and a second service call.

Whether you've got a single DCVA on an irrigation system or dozens across a commercial property portfolio, we'll keep them tested, compliant, and working properly. Give us a call or request a quote online — we're happy to help.