What it is
The Apollo DC4A (DCLF4A lead-free; 4A-100 / 4ALF-100 series) is a bronze double check valve assembly in ½" through 2" with top-access check cartridges, four top-mounted test cocks, and ball-valve shutoffs. It is used where the hazard is low enough for a DC: irrigation, some commercial services, fire lines at the small end.
Length and height above the pipe match the RP4A exactly: 12⅝" at ¾", 20⅛" at 2", 3½" to 5" above centerline. Apollo's sheet does not publish a below-centerline figure; with no relief valve there is little there.
What matters for the cover
Same covers as the RP4A. The 20 × 20 at ¾", the 24 × 24 at 1", the 30 × 24 at 1¼" through 2", the 36 × 24 if a strainer is installed. One bin serves both assemblies.
Base closes fully. No relief discharge. Close the cover to the pad, keep the ground heat in, and let the wind find nothing to lift.
Riser height. On irrigation installs the DC often stands on a riser at the point of connection. Measure pad to the top of the test cocks and add a few inches for closure.
Small DCDA4A. Apollo makes a 1½" and 2" detector version. Photos first; the bypass changes the width.
Stocking
In Apollo territory the DC4A is the irrigation double check where the utility allows one, moving in case quantities of the 20 × 20 and 24 × 24 through irrigation supply. Where an RP is required, the RP4A takes over and shares the covers. See the DCV covers page for the category.
Ordering
Name the size and whether a strainer is installed. The 20 × 20 (¾") and 24 × 24 (1") are the everyday answer; 1¼" through 2" take the 30 × 24, or the 36 × 24 with a strainer. Because the DC4A shares its envelope with the RP4A, a counter that stocks for one has already stocked for the other, and the bins do not need a separate label. If the assembly is the small DCDA4A with the bypass, send a photo before quoting.