Irrigation Backflow Winterization and Startup
Purpose
The laterals are not what freezes and splits. The assembly is: a brass or bronze body full of water that cannot be drained the way a buried pipe can, sitting above grade where the cold gets to it first. And the two visits are one job, six months apart, run by two different techs. What the fall visit writes down about what it could not drain is the only thing that tells the spring tech where to expect a split before they put 60 psi behind it and stand next to it. This procedure ties the two halves together through one record.
Scope
Covers fall winterization and spring startup of a residential or light commercial irrigation service and its backflow assembly: pressure vacuum breaker, spill-resistant vacuum breaker, double check or reduced pressure principle, from the assembly's supply valve to the zone valves.
Does not cover interior hose bib winterization, which the hose bib winterization SOP owns, or the vacuum breaker on a hose bib, which the hose bib vacuum breaker verification SOP owns. Does not cover repairing a failed assembly, owned by the backflow assembly repair and retest SOP, or irrigation controller and zone valve troubleshooting.
Roles and responsibilities
| Role | What they own | The handoff |
|---|---|---|
| Office | Booking both halves as one job and carrying the fall record into the spring ticket | Attaches the fall record to the spring ticket; a spring visit without it starts blind |
| Technician | The isolation, the drain, the blowout pressure, the undrainable list, the spring retest | Returns what could not be drained and why; that list is the spring visit's inspection plan |
| Lead or owner | An assembly that cannot be protected where it stands | Owns the enclosure, relocation or removable-riser decision rather than a tech deciding to leave it |
Procedure
Shut the irrigation supply and take the controller out of the picture before anything else. Close the assembly's number 1 supply valve, put the controller in off rather than rain delay, and tell the customer both are done. Acceptance: supply valve closed, controller confirmed off at the faceplate, customer told in writing. Wrong looks like relying on rain delay, which expires on its own schedule. Stop rule: a controller you cannot positively switch off gets its common wire lifted or its power pulled before air goes near a zone. Hazard: a zone starting while you are over an open head or a charged blowout line is a face full of water and grit at pressure, so the controller is dead before a fitting is opened.
Identify the assembly and read its winterizing method, because the type decides what can be drained. Record type, make, model and serial, then find the manufacturer's winterizing instruction for that model. Acceptance: type and model recorded, the manufacturer's method identified, and a note of whether a heated enclosure exists. Wrong looks like treating all four types the same, when a reduced pressure assembly keeps its body wet through the relief and a vacuum breaker traps water in the bonnet above its check. Stop rule: an assembly outdoors with no heated enclosure and no manufacturer-approved way to drain it goes to the lead as an enclosure or removal decision, not left to chance. Hazard: none created here; it is a nameplate read and a document check.
Drain by the manufacturer's method and write down every void you could not empty. Open the test cocks and any drain the instruction names, in the order it gives, and let the body clear. Acceptance: every test cock opened and passing no water, the body drained by the stated method, and an explicit written list of any void, bonnet or cavity that could not be drained. Wrong looks like opening two cocks, seeing water stop and calling it drained, which leaves the bonnet full above a closed check. Stop rule: a drain plug or test cock that will not open is recorded as an undrainable void rather than forced, because a snapped test cock in November is a replacement, not a repair. Hazard: the body may still hold line pressure if the supply valve is passing, so crack the first cock slowly with your face out of its line and confirm the flow stops before opening the rest.
Blow out the laterals downstream of the assembly, never through it, and never above the published pressure. Connect air at the blowout port on the downstream side, set the regulator at or below the maximum blowout pressure the pipe and head manufacturers publish for that material, and run zones one at a time. Acceptance: air introduced downstream of the assembly, regulator set at or below the published maximum with the figure written down, each zone run only until it turns from water to mist and no longer than the head manufacturer's stated run limit, and never a zone left closed with the compressor feeding. Wrong looks like blowing air through the assembly, which drives the checks backward and can unseat a poppet you will then fail in the spring. Stop rule: no published blowout pressure for that pipe material means no blowout until the lead confirms one. Hazard: this is stored energy in a buried system, so nobody stands over a head or a valve box while a zone is charged, eye protection is on, the compressor is bled to zero before any hose is disconnected, and a stuck head is left alone rather than reached for.
In spring, re-pressurize slowly through the test cocks with every zone still closed. Open the number 1 supply valve slowly, purge air through each test cock until a solid stream shows, close them, then open number 2. Acceptance: a solid air-free stream from every test cock, number 2 opened only after the cocks are closed, and no water appearing anywhere outside a fitting. Wrong looks like opening the supply fast with the zones open, which slams an air-water slug into the checks and into the heads. Stop rule: water appearing at the body, a bonnet or a seam is a freeze split, so the supply closes immediately and nothing is re-pressurized until it is repaired. Hazard: this is the step that puts pressure back, and a freeze-cracked body announces itself here as a jet at line pressure, so open the valve from the side rather than standing over the assembly, and keep the customer and any helper back until it has held for a minute.
Hold line pressure and inspect for freeze damage before any test is run. Leave the assembly at line pressure with the zones closed and inspect the body, bonnet, test cocks and the first fittings each side. Acceptance: no weeping anywhere after 10 minutes at line pressure, no relief discharge on a reduced pressure assembly, and every point on the fall visit's undrainable list inspected by name. Wrong looks like going straight to the test, which puts a gauge on an assembly whose body may already be split. Stop rule: a cracked body is a replacement rather than a rebuild, and a cracked bonnet or cover is repaired only where the manufacturer lists that part separately. Hazard: an assembly holding pressure with a hairline crack can open suddenly, so the inspection is done from the side with eye protection on and nothing is tapped, flexed or wrenched while it is pressurized.
Run the full test for that assembly type, then start the zones and file. Test to the field test procedure your purveyor has adopted, then return the controller to service and run each zone once. Acceptance: an actual reading for every test the type requires, all at or above the minimum, the controller programmed and confirmed, every zone run once with heads observed, and the report filed inside the purveyor's window. Wrong looks like starting the zones first and testing afterward, which puts debris through an assembly you have not yet proved. Stop rule: any test below its minimum leaves the irrigation supply closed and hands the assembly to the repair and retest SOP; the system does not run on a failed assembly. Hazard: walking zones means being beside popping heads and open valve boxes, so eye protection stays on, the customer stays off the lawn while zones cycle, and any box lid removed is replaced before you move on.
The record this produces
One record covering both visits: assembly type, make, model and serial; whether a heated enclosure exists; the manufacturer's winterizing method used; the written list of voids that could not be drained; the blowout pressure used and the published maximum it was set against; zones blown and their run times; the spring purge observation; the 10 minute hold result with each undrainable void inspected by name; every spring test reading against its minimum; and the filing date.
The undrainable list is the field that makes this one job instead of two. A spring tech who knows the bonnet went into December full does not stand in front of it, and the shop can quote a bonnet before the visit rather than after. The office reads the enclosure line to know which properties need the lead's decision before the next fall. The lead reads repeat splits at the same property as an enclosure or relocation conversation, not another part.
One worked pass, including a failure
A residential irrigation service with a pressure vacuum breaker above grade and six zones, no enclosure, winterized in the fall by one tech and started in the spring by another.
The fall visit closes the supply valve, confirms the controller off at the faceplate rather than on rain delay, and records type, make, model and serial. The manufacturer's method drains the body through the test cocks, and both open and clear. The bonnet is the problem: the instruction shows no drain provision for it on this model, so the fall record carries one line under undrainable voids reading "bonnet above the check, no drain provision on this model, not drained." The laterals are blown from the downstream blowout port, never through the assembly. The fall record notes the published maximum blowout pressure read from the pipe manufacturer's literature for that lateral material as 50 psi, and the regulator is set to 45 psi, which is 5 psi under. Each of the six zones is run once until it turns to mist, none longer than the head manufacturer's stated limit, and the compressor is bled to zero before the hose comes off.
Spring startup fails at re-pressurization. The number 1 valve is opened slowly from the side and the test cocks purge solid, but as the body comes up a fine jet appears from a split in the bonnet seam, at the exact void the fall record named. The supply closes immediately. Nothing is tested, nothing is re-pressurized, and the customer is told the system stays off until the part arrives. Because the fall record named the bonnet, the shop had the part number before the tech left the driveway rather than after a second trip.
The bonnet is listed separately by the manufacturer for this model, so it is replaced rather than the whole assembly. Re-pressurized the same way, the assembly holds 10 minutes with no weeping at body, bonnet, cocks or the first fittings each side, and the bonnet is inspected by name because it is on the undrainable list. The test then reads the air inlet opening at 1.6 psid against a 1.0 psid minimum, so 0.6 psid of margin, and the check holding at 1.3 psid against the same 1.0 minimum. Both clear. Controller returned to service, all six zones run once with heads observed, report filed.
References
- The field test procedure your water purveyor has adopted, which binds you through that purveyor's cross-connection control program and your tester certification, and which sets the minimums used in step 7.
- Assembly manufacturer literature for the winterizing method, the drain provisions that exist on that model, and which parts are listed separately for repair under the step 6 stop rule.
- Pipe and head manufacturer literature for the published maximum blowout pressure and zone run limit used in step 4; there is no universal figure, and the number goes on the record.
- See related: the Plumbing backflow assembly repair and retest SOP, the cross-connection survey of a property SOP, the hose bib vacuum breaker verification SOP, and the hose bib winterization SOP.