Sub Zero Covers
Large green insulated backflow cover wrapped around a wide double-check detector assembly, with the red valve stems and chain left above the cover for testing.
Wide assembly — valve stems left clear for testing

By assembly and size

3" RP backflow cover

3" RP backflow cover sizing starts with the assembly on the tag. At 3", 10 RP assemblies from the brands we pattern for are common: Watts 909 / LF909, Watts 957 / 957Z, Febco LF860 Large, Zurn Wilkins 375 / 375A / 375AST, Zurn Wilkins 475 / 475V, Ames 4000SS, Ames Colt C400, Apollo / Conbraco RPLF4A large, Deringer (Ames) 40, and Deringer (Ames) 40G / 50G. 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 "3" RP" covers on a counter

Reduced pressure zone (RP / RPZ). At 3" the assemblies your customers bring in are Watts 909 / LF909, Watts 957 / 957Z, Febco LF860 Large, Zurn Wilkins 375 / 375A / 375AST, Zurn Wilkins 475 / 475V, Ames 4000SS, Ames Colt C400, Apollo / Conbraco RPLF4A large, Deringer (Ames) 40, and Deringer (Ames) 40G / 50G. They are not the same size: the Deringer (Ames) 40 is 18.7" end to end and the Watts 909 / LF909 is 42.5", so "a 3" RP" is not a single envelope.

The stock cover for 3"

The April 2026 price list maps 3" 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.

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 RP 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

3" reduced pressure zone 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 909 / LF90942.5"18.875"5.25"70 × 40 (DS7040) · N-shape NS3
Watts 957 / 957Z31.75"18.875"6.6875"70 × 40 (DS7040) · N-shape NS3
Febco LF860 Large41.875"12.125"11.375"70 × 40 (DS7040) · N-shape NS3
Zurn Wilkins 375 / 375A / 375AST32"12.75"9.5"70 × 40 (DS7040) · N-shape NS3
Zurn Wilkins 475 / 475V · N-pattern———N-shape NS3
Ames 4000SS38"18.875"10.5"70 × 40 (DS7040) · N-shape NS3
Ames Colt C40031.75"18.875"6.6875"70 × 40 (DS7040) · N-shape NS3
Apollo / Conbraco RPLF4A large32"20.5"9"70 × 40 (DS7040) · N-shape NS3
Deringer (Ames) 4018.7"7.4"8.7"70 × 40 (DS7040) · N-shape NS3
Deringer (Ames) 40G / 50G31.9"19.5"9.3"70 × 40 (DS7040) · N-shape NS3

Common questions

Which cover fits a 3" RP?
The 70 × 40 (DS7040) is the price-list match for 3". N-pattern installs take the N-shape NS3 instead.
Do all 3" RP assemblies take the same cover?
Not always. At this size the published lengths run from 18.7" (Deringer (Ames) 40) to 42.5" (Watts 909 / LF909). 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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