Sprinkler Winterization and Fall Blowouts
Water left in a line freezes, expands, and splits whatever it is sitting in. A blowout is the cheapest thing you will do to an irrigation system all year.
Why draining is not enough
Gravity takes out the water that can run downhill. It does not take what is held in the lateral lines, inside the heads themselves, or in any run that sits below the drain point. That is the water that freezes, and a line only has to hold a little of it to split.
Compressed air clears the rest, and it is the volume of air that does the work rather than the pressure on the gauge. A small workshop compressor can show a high number without ever moving enough air to carry water out of a zone. That is how a system gets blown out and still fails in January.
How the blowout runs
- The supply is shut off at the main and the system is isolated.
- Air is introduced and each zone is opened in turn, one at a time, until the heads run dry and stop misting.
- Zones are cycled in short passes rather than held open, because running a rotor dry under air heats its gears.
- The backflow assembly is drained and left so nothing can collect and freeze inside the body.
- The controller is shut down for the season, or set to its off position so it keeps its programme.
Book before the freeze, not after
This is booked before the first hard freeze rather than after the first cold night. On this side of the escarpment the ground can freeze early, and the fortnight before that happens is the busiest stretch of the irrigation year for everybody in the trade. Getting on the list in September rather than late October is the difference between a date that suits you and whatever is left.
A light overnight frost does no harm to a system that is still full. Sustained freezing does. The risk is not one cold night in October. It is the week when the temperature stops climbing back above zero and nobody in the trade has a slot.
The backflow is the expensive part
Of everything in a residential system, the backflow assembly is the piece that costs real money to replace, and it is the piece most exposed to freezing, because it sits above ground with water held in a metal body. A split lateral or a cracked head is a smaller repair. That assembly is most of the reason this appointment exists.
If it has already frozen
Call anyway rather than waiting for spring. It is worth checking a system for splits before it is charged, instead of finding them by pressurising it and watching where the water comes up. That check is part of the spring startup in any case.
Winterization & blowouts, asked and answered
When should the blowout be booked?
Before the first hard freeze rather than after the first cold night. Booking in early autumn rather than late is the safer side to be wrong on, and the calendar fills from the outside in.
Can I just drain it myself?
Draining removes standing water but not what is held in the lateral lines and the heads. Compressed air clears those, and it takes the volume of air a proper compressor moves rather than the pressure a small one shows.
What actually breaks if it is not blown out?
Most often the backflow assembly, because it sits above ground with water in a metal body. Split lateral lines and cracked heads happen too, and both are cheaper. None of it shows up until the system is charged again in spring.
Does the blowout itself damage anything?
Not when the zones are cycled rather than held open. Running a rotor dry under air for a long stretch heats its gears, so each zone gets short passes rather than one long one.
I missed it this year. What now?
Call. The system gets opened carefully in spring and checked for splits before it is pressurised, which is a much better way to find damage than the other one.