Double Check Valve Enclosures: Best Way To Protect DC Assemblies

Double check valve enclosures are above-ground protective covers that shield DC backflow assemblies from freezing, vandalism, theft and physical damage while preserving access technicians need for testing and maintenance.

The governing standard for these enclosures is ASSE 1060, which sets requirements for structural strength, drainage, security and freeze protection. Because a double check assembly can fail without any visible warning, the enclosure protecting it has to do more than keep the rain off.

Here’s how the assembly works, why it needs protection and how to specify the right enclosure for your project.

A double check valve assembly (DC) is a backflow preventer built around two independently operating spring-loaded check valves installed in series between two shutoff valves. Any time pressure on the property side exceeds pressure on the city side, the check valves close and stop water from flowing backward into the public supply. If the first check fails to seal because of debris or a mechanical issue, the second check provides redundancy.

A DC assembly that’s working properly is invisible in the best sense. The trouble is that a DC assembly that’s failing is invisible, too. Because the device is a closed system with no relief valve, it has two inherent blind spots:

1. No visible indication the check valves are working. A DC has no mechanism that reveals whether its internal checks are sealing properly. An RPZ dumps water from its relief valve when something is wrong. A DC gives you no such indicator.
2. No way to detect debris without a full test. A pebble, scale fragment or other contaminant lodged in a check valve can hold it partially open. The only way to find out is a differential pressure test by a certified backflow tester.

Because a double check assembly can fail silently, the enclosure around it matters even more. The device depends entirely on regular testing to prove it’s working, so anything that blocks access to the test cocks, buries the assembly in a flooded vault or lets it freeze solid undermines the whole cross-connection control program.

Once the assembly is specified, the next design decision is how to protect it. Double check valve enclosures address three risks that show up on real installations again and again.

1. Freeze Damage Happens Where You Least Expect It

Property owners still improvise cold-snap protection with towels, tarps and overturned trash cans. Facility-scale assemblies deserve better.

Water trapped inside a check valve expands as it freezes and can crack the valve body, and a single overnight freeze is enough to do it. Sun Belt cities have learned this the hard way across Florida, Texas and Arizona. A heated ASSE 1060 Class I enclosure keeps the assembly above 40°F even when outside temperatures drop to -30°F, with no seasonal winterization to schedule and no risk of doing it late.

2. Theft and Vandalism: Brass Assemblies Are Scrap-Metal Targets

Backflow assemblies are heavily constructed of brass and copper, which makes them frequent targets for scrap metal thieves. A wire cage advertises exactly what’s inside it, but a solid lockable enclosure conceals the assembly entirely and removes both temptation and opportunity. ASSE 1060 requires lockable access on every certified enclosure by keyed device or padlock.

3. Testing Access: Annual Testing Requires Clearance

Most jurisdictions require DC assemblies to be tested at least annually by a certified backflow tester. The enclosure has to make testing easy.

ASSE 1060 requires test cocks, valve handles and handwheels to sit within 24 inches of an access opening, and typical design practice calls for 6 to 12 inches of clearance between the assembly and the enclosure walls so technicians can connect test equipment.

A properly sized enclosure with removable panels gives a tester full access without disassembling anything. A tight-fitting cage does the opposite, and a below-grade vault turns a routine test into an OSHA confined space entry.

We manufacture our enclosures from 5052-H32 marine-grade aluminum because the material is durable enough to outlast the equipment it protects. Some of our enclosures have been in the field for three decades!

We use a modular panel system to build enclosures in varying sizes without changing the style or machining special parts, which keeps assembly simple on site. We offer standard enclosure models as well as custom enclosures.

Installation of double check valve enclosures must also comply with local plumbing codes and regulations, and jurisdictions differ on hazard classifications, testing frequency, setback requirements and approved device lists. Before finalizing a design, verify both the assembly and the enclosure against the standard details published by your water purveyor. When the local detail is silent on enclosures, following ASSE 1060 gives you good specification language.

Whether you’re writing a specification, reviewing standard details or replacing a freeze-damaged assembly, the right enclosure protects the device and the potable water supply behind it. Use the Safe-T-Cover sizing guide to match your double check valve assembly to an ASSE 1060-compliant enclosure, or contact a Safe-T-Cover design engineer for help.