Sub Zero Covers
Three green insulated backflow covers in a gravel bed outside an office building — a large double-check detector assembly, a mid-size assembly, and a small companion cover.
Office campus — a whole backflow fleet on one cover line

By assembly and size

2½" RPDA backflow cover

2½" RPDA backflow cover sizing starts with the assembly on the tag. At 2½", 3 RPDA assemblies from the brands we pattern for are common: Ames Colt C500, Apollo / Conbraco RPDALF4A, and Deringer (Ames) 50. The price list maps this pipe size to one stock cover, and the published dimensions below say which one to pull.

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What "2½" RPDA" covers on a counter

Reduced pressure detector assembly. At 2½" the assemblies your customers bring in are Ames Colt C500, Apollo / Conbraco RPDALF4A, and Deringer (Ames) 50. They are not the same size: the Deringer (Ames) 50 is 18.7" end to end and the Apollo / Conbraco RPDALF4A is 31", so "a 2½" RPDA" is not a single envelope.

The stock cover for 2½"

The April 2026 price list maps 2½" to 70 × 40 (DS7040), with the N-shape NS3 for N-pattern installs. That cover was built around this size class; the table below shows how each assembly sits inside it.

Relief valve drainage

Every assembly on this page has a relief valve that discharges downward from under the body. Leave that path open. Close the cover to the pad around the assembly, never under the relief port.## The detector bypass

RPDA assemblies carry a metered bypass along one side of the mainline. It adds width the stock cover usually accommodates at this size, but send a photo showing the bypass side before quoting; a custom pattern ships in 3–5 business days.

When to measure instead

Unions, strainers, OS&Y gates, and wall-tight mounts all move an assembly off its spec sheet. If the tag is gone or the install is odd, measure it or send photos for a custom cover. For the type as a whole see RPDA covers; for another size, start at the fitment hub.

Sub Zero Covers sells through distributors only. Distributor accounts see pricing and availability in the portal; everyone else orders through their supply house, or applies for distributor access.

Assemblies at this size

2½" reduced pressure detector assembly assemblies and the cover that fits

Dimensions in inches from each manufacturer's spec sheet with standard shutoffs. Length end to end; heights from the pipe centerline. The cover column is the closest stock fit by published length; confirm against the assembly in front of you.

AssemblyLengthAbove CLBelow CLClosest stock cover
Ames Colt C50030.75"16.375"6.5"70 × 40 (DS7040) · N-shape NS3
Apollo / Conbraco RPDALF4A31"16.375"9.625"70 × 40 (DS7040) · N-shape NS3
Deringer (Ames) 5018.7"7.1"8.7"70 × 40 (DS7040) · N-shape NS3

Common questions

Which cover fits a 2½" RPDA?
The 70 × 40 (DS7040) is the price-list match for 2½". N-pattern installs take the N-shape NS3 instead.
Do all 2½" RPDA assemblies take the same cover?
Not always. At this size the published lengths run from 18.7" (Deringer (Ames) 50) to 31" (Apollo / Conbraco RPDALF4A). Order by model.
Is this a heated enclosure?
No. Sub Zero Covers are insulated, unheated covers (R-13 standard, R-30 extreme weather). They are not ASSE 1060 listed enclosures. Where a spec calls for a Class I heated enclosure, ask sales before quoting.

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