Backflow Testing & Prevention
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Plain-English article
Sprinkler Backflow Preventer in Thornton, CO: Winter Care
The brass assembly sticking up from the ground or sitting beside your house is a backflow preventer. It protects the drinking water, and it is the part of a sprinkler system most likely to freeze.
By the Thornton Plumbing Co. team ·
What it does
A sprinkler line connects to the drinking water supply. Should pressure in the city main fall, water from the lawn side could flow backward. The backflow preventer is a mechanical check that stops it.
It matters because lawn water can carry fertilizer, pesticides and soil. The assembly keeps those out of the supply.
Types of assemblies
Common types include pressure vacuum breakers, double check valves and reduced pressure assemblies. The choice depends on the hazard and local rules. A plumber or irrigation contractor knows which your site needs.
They are installed above ground in a spot that drains and is accessible for testing.
Annual testing
Many water providers require a test each year. A certified tester measures how the checks hold, and files a report. Failed devices get repaired or replaced and retested.
Ask your provider what it needs. See backflow testing for what the visit involves.
Drain it before the freeze
Shut off the water to the sprinkler system at the isolation valve. Open the test cocks and the vent on the assembly and let the water drain. Leave the valves halfway open so that any left-over water can expand.
Blow out the irrigation lines with compressed air, or have a contractor do it. Do it before the first hard freeze. A cracked body means replacement.
Fall and spring checklist
Do these on a schedule.
| When | Task | Why |
|---|---|---|
| Autumn | Shut off, drain and blow out lines | Prevent frozen pipe |
| Autumn | Drain the assembly and leave the handles half open | Avoid a cracked body |
| Spring | Open the valve slowly and check for leaks | Avoid a surge |
| Each year | Schedule a test | Meet utility rules |
Insulate and protect
An insulated cover, sometimes called a hot box or a bag, protects a drained assembly from wind and cold. Do not wrap an undrained assembly and assume it is safe.
Check that the enclosure is secure and that critters cannot get in.
Spring start-up
In spring, open the isolation valve slowly to avoid a surge. Check for leaks at the assembly and at the heads. Have the device tested if it is due.
Leaks at the relief valve or the body mean the assembly needs service. If you find a wet area in the yard, see leak detection.
What the backflow device actually does
A sprinkler system is a network of pipes that sits full of water, often with heads that are lower than the soil around them. If the city supply pressure dropped, say during a main break or heavy fire flow, water from those pipes could be pulled backward toward the house. Fertilizer, pesticide residue and groundwater can sit around the heads, so the device between the system and the house line is there to stop that reverse flow.
Most residential systems use either a pressure vacuum breaker, which stands above ground near the valves, or a reduced pressure assembly in a protected box. Each has internal springs, seals and check parts that wear. A device that has never been tested may look perfectly fine and still leak back through a worn seat. For the broader topic, see backflow testing and prevention.
Shutting the system down before a hard freeze
Thornton sits on the high plains, and an early cold snap in October can arrive before many homeowners think about winter. Trapped water expands as it freezes, and that is what cracks the brass body of a backflow device, splits a PVC fitting or bursts a valve box component.
The usual sequence has three steps. Close the supply valve that feeds the sprinkler branch, and open the test cocks or drain points so the device empties. Then blow the lines out with compressed air, one zone at a time, at a pressure the pipe is rated for. Overdoing the air pressure can crack heads and fittings, which is one reason many people hire the winterizing visit out. Leave the handles of the drain points at a half-open position so water cannot refill and freeze.
Spring startup and the first test
In spring, open the supply valve slowly. A sudden rush of water into an empty line makes a pressure spike that can crack a device that survived the winter. Walk each zone, looking for geysers, soggy spots and heads that do not pop up.
If your device failed a test or has been leaking from the relief port, ask a contractor about repairing or replacing it. Testing these assemblies is specialized work that normally calls for a certified tester, so ask to see the certification and what the test report will show. Keep each report in a folder, since the water provider may want a record of your device.
Watering rules still apply
The city of Thornton can place limits on outdoor watering when supplies run short. In a drought stage the rules have allowed at most two watering days a week and a ban on watering from 10 a.m. to 6 p.m. A controller set once in May and forgotten can break those limits without anyone noticing, so look at the schedule after each startup.
A leak between the valve and the heads wastes water all season, and it shows up as a high bill rather than a puddle. If your usage jumps after startup, read the meter with the sprinklers off. Our guide on leak detection explains how the meter test works.
Who should do the work
Blowing out the lines is a job some homeowners handle, and many hire it out for safety. A compressor with too much pressure, or a user standing in front of a valve box, can cause injury. Ask any contractor which pressure they use and how they protect the heads. Keep the invoice with your backflow test record.
Quick answers
Asked about backflow preventer
Springs and seals wear. Testing confirms it will stop reverse flow.
Before the first hard freeze, usually in autumn.
A cracked body needs replacement.
A certified tester. Ask your provider.
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