The pressure vacuum breaker on your sprinkler line is the most exposed part of the system. How to protect it through a High Desert winter, with the drain steps from the FEBCO and Zurn Wilkins manuals.
Get a Free Irrigation EstimateThe surest way to protect a sprinkler backflow preventer from freezing is to drain it before the first hard freeze and leave its valves and test cocks half open for the winter. Insulation helps, and it is the right move if you keep watering in winter, but FEBCO says its 765 must be drained for the winter where freezing may occur. Whatever you use, never cover the air vent.
If your sprinkler line has a pressure vacuum breaker (PVB) or similar backflow preventer standing above ground, it sits in the open, full of water, on nights that reach 20°F or colder in about 6 of 10 years at Victorville and 7 of 10 years at El Mirage (NOAA 1991-2020 normals). Water expands about 9% when it freezes (USGS), and the brass body and bonnet have nowhere to give.
This page covers insulation first, then the manufacturer drain steps for two pressure vacuum breakers: the FEBCO 765 and the Zurn Wilkins 720A. Other models differ, so read your model plate before you touch a valve.
Freeze risk depends a lot on where you live. NOAA’s normals show about 32 nights a year at or below 32°F at the Hesperia 2E station, about 54 at Victorville, and about 70 at El Mirage on the west side (NOAA NCEI). The median first freeze is November 11 at Victorville, November 12 at El Mirage and December 1 at Hesperia 2E.
The manufacturers are clear about the risk. Zurn’s instructions for the Wilkins 720A say the PVB may be installed outdoors only if the device is protected against any freezing conditions, and that the installation location must be kept above 32°F (Zurn Wilkins 720A). FEBCO’s winterization sheet says its assemblies must be drained for the winter in areas where freezing temperatures may occur (Watts/FEBCO 765). The City of Hesperia lists irrigation control valves among the pipes at risk each winter (City of Hesperia).
Drain valve positions, numbering and parts differ by model, and by how the installer plumbed your line. Look for the maker and model cast or stamped on the body or on a tag before you follow any steps.
| What the plate says | What to do |
|---|---|
| FEBCO 765 | Follow the FEBCO 765 steps below and the Watts winterization sheet. |
| Zurn Wilkins 720A | Follow the Wilkins 720A steps below and the Zurn instructions. |
| Rain Bird PVB | Discontinued. A backflow parts seller lists it as produced from 1982 to 1993 (backflowparts.com), and we found no current Rain Bird manual for it. Rain Bird’s current residential backflow-type product is the ASVF anti-siphon valve (Rain Bird). The drain logic on older PVBs is similar to the two models here, but without a manual, call an irrigation pro before you take one apart. |
| Anything else | Find that maker’s installation or winterization sheet by model number, or have a pro look at it. |
Insulation slows heat loss. It does not make a full, undrained device freeze-proof, which is why FEBCO and Zurn both talk about draining. Insulation makes sense in two cases: over a drained device as extra protection, and on a device you keep in service because you water in winter.
Store-bought insulated covers and bags work on the same idea. Cover ratings vary by product, so do not assume any cover protects to a given temperature unless the maker says so for your size and model.
From the Watts/FEBCO 765 winterization instructions (IS-F-765). Letters match the valve labels in that sheet. Two notes come first in the manual: the assembly can not be adequately drained through the testcocks, and drain valves must be installed on the inlet and outlet sides below the assembly.
The manual’s notice: keep the main shut-off (A) closed all winter. Rain Bird recommends an irrigation specialist for compressed-air blowouts because of the safety risks (Rain Bird).
From the “Drain Procedure for Freeze Protection” in Zurn’s 720A instructions (Zurn Wilkins 720A). Numbers match the valve labels in that sheet.
Zurn’s caution: make sure the main shut-off (1) stays tightly closed all winter so the system cannot refill, and that it seals without leaking.
Read the full procedure in the Zurn sheet before you start. If your PVB has no drain valves on either side, step 6 is Zurn’s answer: take the internals out for winter, or have a pro do it.
It looks odd to leave a ball valve at 45 degrees, but FEBCO explains it: water trapped between the ball and the body of a fully open or fully closed ball valve can freeze and damage the valve (Watts/FEBCO 765). Half open lets that pocket drain. Both manuals above call for the same position on every shut-off, drain and test cock for the winter.
We did not find a manufacturer procedure for a frozen PVB, so this is general practice. Close the irrigation shut-off, usually a brass gate or ball valve just after the tee where the irrigation line leaves the house supply (Rain Bird valve guide). That keeps the house on while the sprinkler side is isolated. Let the device thaw on its own, then look for cracks in the body, bonnet and test cocks. A cracked device gets replaced, not patched.
Replacing a backflow preventer is part of Monarch’s irrigation repair work, and our irrigation cost guide covers what drives the price. For the rest of the system, see how to winterize sprinklers in the High Desert, and for valves that leak after a freeze, sprinkler valve leaking. When to do all this each year is on the High Desert yard care calendar, and local freeze dates by station are in our frost dates and growing zones guide. The full cluster starts at the High Desert irrigation guide.
A cover slows heat loss, but the manufacturers still call for draining. FEBCO says its 765 assemblies must be drained for the winter in areas where freezing temperatures may occur. A cover makes the most sense on top of a drained device, or on one you keep in service for winter watering.
Not a FEBCO 765. The FEBCO winterization sheet says the assembly can not be adequately drained through the testcocks, and it calls for drain valves on the inlet and outlet sides below the assembly.
Water trapped between the ball and the body of a fully open or fully closed ball valve can freeze and damage it, according to FEBCO. Leaving it at 45 degrees lets that water drain.
Not the air vent. Zurn says not to block the air vent opening with insulation, and Rain Bird says not to block the air vents and drain outlets on backflow preventers.
Check the model plate. A backflow parts seller lists the Rain Bird PVB as produced from 1982 to 1993, and we found no current Rain Bird manual for it. The drain idea is similar to the FEBCO 765 and Wilkins 720A, but without a manual it is safer to have an irrigation pro winterize or replace it.
We checked every number on this page against the public sources below. If a rule or date changes, the agency page is the final word.
Monarch installs and repairs sprinkler systems across the High Desert, including backflow preventers and the valves behind them. Get a free estimate and a straight answer on whether yours can be saved.
Get a Free Irrigation EstimateOr call (760) 792-7627
