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

Model fitment

Watts 800M4 PVB cover

Watts 800M4 PVB cover: The 800M4 is the pressure vacuum breaker on a large share of residential and light-commercial irrigation systems. It is small, it is vertical, and it sits on a riser, which means the cover is sized to the install, not just the valve.

Request distributor access Talk to sales

What it is

The Watts 800M4 (LF800M4 in lead-free) is a pressure vacuum breaker in ½" through 2" for irrigation and other non-continuous-pressure applications. Water comes in from below, passes a check and an air inlet, and leaves through a side outlet. Two test cocks, ball-valve shutoffs, and a plastic bonnet on top that vents when the system drains.

The valve itself is small: 6½" wide and about 6½" tall at ¾", 10⅝" wide and under 10" tall at 2". What makes the install tall is the riser. Code puts the PVB 12" above the highest downstream head, so the assembly often stands two feet or more above grade.

What matters for the cover

Height is the riser plus the valve. Measure from the pad to the top of the bonnet. Our 20 × 20 and 24 × 24 closed-top covers are the price-list match at ¾" and 1"; on a tall riser the 24 × 24 is the one. Above roughly 20" of exposed riser, or on 1½" and 2" units, move to the 30 × 24.

Do not compress the bonnet. The air inlet has to open when the system is off. The cover should sit over the valve, not pull down on it.

Two ball-valve handles stick out from the body on the M4QT version. They add width; the closed-top covers allow for it.

Drain first, then cover. A PVB that is still charged in a hard freeze will crack; the cover buys hours, not a season. The winterization guide covers the shutoff-and-drain sequence contractors use.

Stocking

This is the highest-velocity cover SKU in irrigation supply: ¾" and 1" 800M4s by the pallet, mostly in the Sunbelt where systems stay charged through winter. Case quantities of the 20 × 20 and 24 × 24, stocked by October, sell through on the first freeze forecast. See the PVB covers page for the category and the Febco 765 for the other PVB your counter will see.

Two covers for the whole install

The 20 × 20 and 24 × 24 handle nearly every ¾" and 1" 800M4 on a residential riser, which is why they are the two highest-volume SKUs in the catalog. Buy them in case quantities in September; they are the covers that sell out during the first forecast, and reorders placed in the forecast ship after the thaw.

Published dimensions

Watts 800M4 / LF800M4 envelope, by size

Pressure vacuum breaker. Dimensions in inches from the manufacturer's spec sheet with standard shutoffs. This is a vertical unit: the first column is the width and heights are overall; add the riser above grade. The stock cover column is the price-list mapping for that pipe size, ordered closest fit first.

SizeWidthAbove CLBelow CLStock cover
¾"6.5"2.5625"3.9375"20 × 20 (DS2020), 24 × 24 (DS2424)
1"7.5"2.75"4.75"20 × 20 (DS2020), 24 × 24 (DS2424)
1¼"8.875"3.25"5.75"30 × 24 (DS3024), 36 × 24 (DS3624), 42 × 24 (DS4224)
1½"9.25"3.25"6.25"30 × 24 (DS3024), 36 × 24 (DS3624), 42 × 24 (DS4224)
2"10.625"3.25"6.375"30 × 24 (DS3024), 36 × 24 (DS3624), 42 × 24 (DS4224)

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 1" Watts 800M4 on a 12" riser?
The 24 × 24 closed-top cover (DS2424). Total height from pad to bonnet is roughly 12" of riser plus about 7" of valve; the 24" cover clears it with room to close at the base.
Can I leave the irrigation system charged and rely on the cover?
For a single cold night in a mild climate, an insulated cover carries a charged PVB through. For a multi-day event, shut the isolation valve and drain the assembly; the cover then protects against the surprise frost, not the siege.
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 Watts product?
No. Sub Zero Covers is an independent manufacturer. We pattern covers to the published dimensions of Watts assemblies; Watts does not endorse or supply them.

Related pages