How to Winterize an Irrigation Backflow Preventer in Upstate SC

To winterize an irrigation backflow preventer, shut off the water feeding it, open the inlet and outlet drain valves, open every test cock, and leave the ball valves and test cocks at a 45-degree half-open angle for the winter. If you blow out the sprinkler lines, put the air in downstream of the assembly, never through it. Keep the main irrigation shutoff closed until spring.

That's the short version. Upstate winters are mild most days, but a few hard nights are enough to split a brass body or crack a ball valve that was left full of water. Here's how the manufacturers say to do it, what Greenville Water and Spartanburg Water expect, and where a certified tester fits in.

Why does a backflow preventer freeze before the rest of the system?

Most irrigation backflow assemblies sit above ground, often against a north wall or out by the meter, with nothing between the water and the air but brass and a thin cover. Buried pipe below the frost line holds some warmth. The assembly doesn't.

The ball valves are the weak spot. FEBCO's freeze protection sheet for the Model 765 pressure vacuum breaker explains that a ball valve left fully open or fully closed traps water between the ball and the valve body. When that pocket freezes, the valve is damaged. That's why every manufacturer procedure ends with the valves set halfway.

Both Greenville Water's Cross Connection Control Manual (section 5-4.8) and Spartanburg Water's manual (section 9.3) require RP and double check assemblies to sit in an enclosure or building that protects them from freezing, traffic, and vandalism. An enclosure helps a lot, but a seasonal irrigation line still needs to be drained.

How do you drain a pressure vacuum breaker or RP assembly?

The steps below follow the Watts winterization instructions for the 765 PVB and the Watts freeze protection guide for Series 850 and 860 double check and RP assemblies. Other brands are similar, but check the manual for your model.

1. Close the main irrigation shutoff that feeds the assembly. Watts says this valve should be resilient seated so it doesn't seep water back in over the winter.
2. Open the inlet drain valve on the supply side, below the assembly.
3. Turn both assembly ball valves to 45 degrees.
4. Open all the test cocks.
5. Open the outlet drain valve on the downstream side.
6. On a double check or RP, remove the cover and the inlet check module so the water inside the body drains back out through the inlet drain. That step comes from the Series 850/860 guide.
7. On an RP only, loosen the relief valve cover to let it drain, then snug it back down.
8. Leave everything half open for the winter: drain valves, test cocks, and ball valves. Leave the main shutoff closed.

FEBCO and Watts both make the same point up front: you can't adequately drain an assembly through the test cocks alone. If your installation has no drain valves on the inlet and outlet sides, that's worth fixing before next fall. The manufacturers say drain valves belong below the assembly, preferably below the freeze line.

Can you blow out sprinkler lines through the backflow preventer?

No. Blow out the lines downstream of it. The 765 procedure is specific: make sure the outlet drain valve is open, close the assembly's outlet shutoff, connect the air line to the outlet drain valve, and clear the downstream piping. When you're done, open the shutoffs back to the 45-degree position.

Salt Lake City's utility puts the reason plainly in its winterizing guide: blowing high-pressure air through the backflow preventer may damage the device. Checks and seats are built to handle water, not a compressor's worth of air.

If you're not comfortable with a compressor, this is a good job to hand to an irrigation contractor.

Should you remove the assembly for the winter?

Some Upstate irrigation companies tell homeowners to pull the assembly at its unions, drain it, and store it indoors until spring. That works mechanically, but it raises a compliance question.

South Carolina's State Primary Drinking Water Regulation R.61-58.7 says each assembly is tested by a certified tester after installation and before use, at least annually, and immediately after repairs of any kind. The South Carolina Residential Code, section P2503.8.2, adds relocation to that list. Whether a seasonal remove-and-reinstall counts as an installation is a call your water utility makes, not something to guess at.

Before you pull an assembly, email or call the utility's cross connection office. In Greenville that's the Cross Connection Control Program at bfp@greenvillewater.com, listed on Greenville Water's backflow prevention page. If anything gets repaired or replaced while the assembly is out, the state rule already settles it: it needs a test.

What do Greenville Water and Spartanburg Water require for irrigation?

They don't treat residential irrigation the same way, which surprises people who work both counties.

Greenville Water. New residential irrigation services get a non-testable dual check valve built into the meter setter. Existing residential systems that use a testable double check are being phased out in favor of that dual check. Testable assemblies on commercial, industrial, and other services must be tested at least once a year, and the customer has 45 days from the scheduled due date to get it done. If an assembly fails and parts are on order, the tester sends the failed report the same day, and the passing retest also goes in the same day. New assemblies must be tested before use, with the report received within 10 days of starting service.

Spartanburg Water. Low hazard residential lawn irrigation needs at least a dual check and is excluded from annual testing. High hazard residential irrigation needs a reduced pressure assembly, tested annually. Other approved assemblies are tested every year, and the utility sends a notice 30 days before the due date. Details are in section 10 of the Spartanburg Water Cross Connection Control Manual.

If you're on Easley Combined Utilities or another system, check with that utility directly. Programs follow the same state rule but set their own procedures.

How do you restart it in the spring?

Wait until the freeze risk has passed. Then, per the Watts Series 850/860 guide:

1. Close all drain valves, test cocks, and ball valves.
2. Retighten the relief valve cover on an RP and reinstall the check module if you pulled it.
3. Slowly open the main shutoff and then the inlet ball valve.
4. Crack each test cock open and closed, one at a time, to bleed air out.
5. Slowly open the outlet ball valve and let the system refill.

Opening valves slowly matters. Slamming a freshly drained line full of water at line pressure is how unions and fittings start leaking.

Then look the assembly over. If it weeps from the relief port, a check is fouled, or a valve won't seat, call a certified tester. A repair means a test, and the report has to reach the utility.

A note for testers heading into spring

Spring restarts tend to pile up in a few weeks, and each retest still means writing readings onto the right utility's form. Psid lets you enter RP, DC, and PVB readings on your phone and fills the published Greenville Water, Spartanburg Water, or Easley Combined Utilities report PDF. You still review it, sign it, and submit it the way the utility asks. There's a 14-day free trial, and pricing is $49 a month after that.