Every fall we get the same question, usually in the first week the mornings turn cold: does the system really need blowing out, or is draining it enough?
It is a fair question, and the answer comes down to what freezing water does to a pipe.
What winter actually does to a system
Water expands as it freezes. In a sealed section of pipe there is nowhere for that expansion to go, so it goes into the pipe wall, the fitting or the valve body — whichever gives first.
Northern Kentucky makes that worse than a colder, steadier climate would. We do not get one long freeze and then a thaw in March. We get a run of nights below freezing, a warm week, then another run. Each cycle works on the same hairline crack, and a fitting that survived December opens up in February.
Three parts of a system take the brunt of it:
- Lateral lines, particularly at low points where water collects
- Valves, where the internals are tight and unforgiving
- The backflow preventer, which on most properties sits above ground and has the least protection of anything in the system
The backflow preventer deserves a mention on its own. It exists to stop irrigation water flowing back into the drinking supply, and replacing one is not a job for a homeowner with a wrench.
Why draining is not the same as clearing
Opening a drain valve and letting the system empty sounds like it should work, and on a perfectly graded system with no low points it nearly would.
Real yards are not graded like that. Water sits in the dips, in the heads themselves and in the valve bodies. There is not much of it, and there does not need to be — a small amount of trapped water in the wrong fitting is all it takes.
A blowout pushes air through each zone until the water is gone. You can see the moment it happens: the heads go from throwing water, to throwing mist, to throwing nothing but air.
What a blowout involves
- Shut the water off at the supply and prepare each zone.
- Connect a commercial-grade air compressor at the backflow preventer.
- Clear the zones one at a time, running each until only mist and air come out of the heads.
- Let the low heads drain, since they hold water after the zone stops.
- Drain and protect the backflow preventer, which is insulated or removed depending on the setup.
- Open the drain valves and inspect, which is when anything already damaged tends to show itself.
The whole visit is usually under an hour on a typical residential system.
Why this is not a good DIY job
The equipment is the first problem. Clearing an irrigation zone needs volume of air, not pressure — a pancake compressor from the garage will happily sit there pushing 120 psi through a line without moving the water anywhere useful.
The second problem is that too much pressure damages exactly what you were trying to protect. Seals, valve diaphragms and older PVC do not enjoy being hit with high-pressure air, and it is easy to do real damage in a few seconds.
And if a zone gets missed, you will not find out until spring.
When to book
Early fall, before the first hard freeze. Most blowouts here happen in October, and the calendar fills quickly once a freeze appears in the forecast.
There is no advantage in waiting for the first frost warning. A system cleared in early October is protected for the season; one booked the week of the freeze is a scheduling gamble.
While we are there
It is worth checking the outdoor lighting at the same time. The failures that show up over winter are usually moisture getting into a connection or a fixture seal that has perished, and both are easier to deal with in October than in January.
If you want the spring start-up booked at the same time, say so when you call. Most customers do, and it means neither visit gets forgotten.
