Sub Zero Covers
Tan insulated backflow cover in a retail parking-lot island, fitted around the assembly with the yellow fire department connection riser left clear.
Retail center — FDC riser left clear of the cover

By assembly and size

2½" double check backflow cover

2½" double check backflow cover sizing starts with the assembly on the tag. At 2½", 8 double check assemblies from the brands we pattern for are common: Watts 757, Watts 774 / 774DCDA, Febco 870V / LF870V, Zurn Wilkins 350 / 350A / 350AST, Ames 2000SS, Ames Colt C200, Apollo / Conbraco DCLF4A large, and Deringer (Ames) 20. 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" double check" covers on a counter

Double check valve. At 2½" the assemblies your customers bring in are Watts 757, Watts 774 / 774DCDA, Febco 870V / LF870V, Zurn Wilkins 350 / 350A / 350AST, Ames 2000SS, Ames Colt C200, Apollo / Conbraco DCLF4A large, and Deringer (Ames) 20. They are not the same size: the Deringer (Ames) 20 is 18.7" end to end and the Watts 774 / 774DCDA is 37", so "a 2½" double check" 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.

The base can close

A double check does not discharge, so the cover can close fully to the pad. That holds ground heat in and gives wind nothing to lift.

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 double check 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" double check valve 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
Watts 75730.75"16.375"3.5"70 × 40 (DS7040) · N-shape NS3
Watts 774 / 774DCDA37"16.375"3.5"70 × 40 (DS7040) · N-shape NS3
Febco 870V / LF870V · N-pattern25.75"——N-shape NS3
Zurn Wilkins 350 / 350A / 350AST31"11.5"3.5"70 × 40 (DS7040) · N-shape NS3
Ames 2000SS37"16.375"3.5"70 × 40 (DS7040) · N-shape NS3
Ames Colt C20030.75"16.375"3.5"70 × 40 (DS7040) · N-shape NS3
Apollo / Conbraco DCLF4A large31"16.4"3.9"70 × 40 (DS7040) · N-shape NS3
Deringer (Ames) 2018.7"7.1"2.9"70 × 40 (DS7040) · N-shape NS3

Common questions

Which cover fits a 2½" double check?
The 70 × 40 (DS7040) is the price-list match for 2½". N-pattern installs take the N-shape NS3 instead.
Do all 2½" double check assemblies take the same cover?
Not always. At this size the published lengths run from 18.7" (Deringer (Ames) 20) to 37" (Watts 774 / 774DCDA). 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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