Sub Zero Covers
Green insulated backflow cover installed against a granite outcrop under a clear blue sky, with a padlocked chain and orange valve stems rising above the cover.
Padlocked and sealed against a hard freeze

By assembly and size

4" double check backflow cover

4" double check backflow cover sizing starts with the assembly on the tag. At 4", 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.

Request distributor access Talk to sales

What "4" double check" covers on a counter

Double check valve. At 4" 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 40", so "a 4" double check" is not a single envelope.

The stock cover for 4"

The April 2026 price list maps 4" to 85 × 40 (DS8540), with the N-shape NS4 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

4" 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 75733.75"22.75"4"85 × 40 (DS8540) · N-shape NS4
Watts 774 / 774DCDA40"22.75"4.5"85 × 40 (DS8540) · N-shape NS4
Febco 870V / LF870V · N-pattern27.875"——N-shape NS4
Zurn Wilkins 350 / 350A / 350AST37.625"14.5"6"85 × 40 (DS8540) · N-shape NS4
Ames 2000SS40"22.75"4.5"85 × 40 (DS8540) · N-shape NS4
Ames Colt C20033.75"22.75"4"85 × 40 (DS8540) · N-shape NS4
Apollo / Conbraco DCLF4A large37.6"22.8"4.6"85 × 40 (DS8540) · N-shape NS4
Deringer (Ames) 2018.7"7.9"2.9"85 × 40 (DS8540) · N-shape NS4

Common questions

Which cover fits a 4" double check?
The 85 × 40 (DS8540) is the price-list match for 4". N-pattern installs take the N-shape NS4 instead.
Do all 4" double check assemblies take the same cover?
Not always. At this size the published lengths run from 18.7" (Deringer (Ames) 20) to 40" (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.

Related pages