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

Model fitment

Deringer 40 backflow cover

Deringer 40 backflow cover: The Deringer 40 is the shortest large RP on the market: under 19 inches end to end through 4 inches, because the butterfly shutoffs are built into the body. The relief valve underneath is not small, though, and the flanged G version is a different animal.

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What it is

The Deringer 40 (now sold as Ames Deringer, a Watts brand) is a reduced pressure zone assembly in 2" through 8" on a 304 stainless body with integral gear-operated butterfly shutoffs and a balanced-chamber relief valve mounted under the body. The 40G swaps the butterflies for flanged OS&Y gates; the X suffix means oversized low-head-loss checks; the 50 is the RPDA with a Type II micro-bypass and meter, in the same envelope.

The standard 40 is 18.7" end to end from 2½" through 4", 25" at 6", 31" at 8", and only 7"–10" tall above the pipe. The relief valve drops 8.7" below centerline through 4" and 10½"–10¾" at 6" and 8". The 40G is roughly twice as long, 32" to 45", with OS&Y stems 19" to 39" above the pipe.

What matters for the cover

Two envelopes under one number. The butterfly 40 at 4" is 18.7" long and about 8" tall above the pipe; the 40G at 4" is 33.9" long and 22½" tall. The price list puts both under the 85 × 40 at 4", and it clears both, but on a butterfly 40 there is a lot of cover for a little assembly. Tell us which you have and, on the compact version, we will often suggest a custom fit that closes tighter.

The 2" is a 2½" body. Deringer builds the 2" as a 2½" assembly with adapters, 22" long. The price list's 1"–2" covers are the match, and the 42 × 24 is the one that clears it.

Relief depth. The relief valve under the body has to drain. Set the cover so the base closes to the pad around the assembly but never seals under the relief port. At 8.7" to 10.7" below the pipe, the relief valve is most of what hangs down.

Type II bypass on the 50. Mounted across the body, it barely changes the footprint. Photos anyway.

Stocking

Deringer shows up where the specifier wanted a small footprint: vault conversions, tight mechanical rooms, retrofit pads. Fire protection distributors see the 50 on fire lines; plumbing houses see the 40 on commercial domestic. Volume is regional and lumpy; the customer who needs one needs it this week. Keep the 70 × 40 and 85 × 40 on the shelf and quote the compact custom fit when the tag says 40 without a G.

Published dimensions

Deringer (Ames) 40 envelope, by size

Reduced pressure zone (RP / RPZ). Dimensions in inches from the manufacturer's spec sheet with standard shutoffs. Length is end to end; heights are measured from the pipe centerline up to the highest point and down to the relief valve or body. The stock cover column is the price-list mapping for that pipe size, ordered closest fit first.

SizeLengthAbove CLBelow CLStock cover
2"22.1"7.1"8.7"30 × 24 (DS3024), 36 × 24 (DS3624), 42 × 24 (DS4224)
2½"18.7"7.1"8.7"70 × 40 (DS7040) · N-shape NS3
3"18.7"7.4"8.7"70 × 40 (DS7040) · N-shape NS3
4"18.7"7.9"8.7"85 × 40 (DS8540) · N-shape NS4
6"25"10.1"10.5"100 × 50 (DS10050) · N-shape NS6
8"31"10.4"10.7"120 × 50 (DS12050) · N-shape NS8

Confirm the fit against the assembly in front of you: unions, strainers, and OS&Y gates add length and height beyond the standard sheet. Cover finder · How to measure

Common questions

Which cover fits a 4" Deringer 40 with the built-in butterfly valves?
The 85 × 40 open-top cover (DS8540) is the price-list match for 4" and clears it easily. Because the assembly is under 19" long and 8" tall above the pipe, a custom pattern that closes tighter is often the better cover; ask.
Is the Deringer 40G the same assembly as the 40?
Same checks and relief valve, but the G uses flanged OS&Y gate valves instead of the integral butterflies. It is nearly twice as long and far taller. Order by the letter on the tag.
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 utility or spec requires a Class I heated enclosure, that is a different product; ask sales before quoting.
Is this an official Deringer product?
No. Sub Zero Covers is an independent manufacturer. We pattern covers to the published dimensions of Deringer assemblies; Deringer does not endorse or supply them.

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